The internal temperature of a building is important – particularly in offices and work environments –for maximizing comfort and productivity. Managing the temperature is also essential for reducing the energy consumption of a building. In the US, buildings account for around 29% of total end-use energy consumption, with more than 40% of this energy dedicated to managing the internal temperature of a building via heating and cooling.

The human body is sensitive to both radiative and convective heat. The convective part revolves around humidity and air temperature, whereas radiative heat depends upon the surrounding surface temperatures inside the building. Understanding both thermal aspects is key for balancing energy consumption with occupant comfort. However, there are not many practical methods available for measuring the impact of radiative heat inside buildings. Researchers from the University of Minnesota Twin Cities have developed an optical sensor that could help solve this problem.

Limitation of thermostats for radiative heat

Room thermostats are used in almost every building today to regulate the internal temperature and improve the comfort levels for the occupants. However, modern thermostats only measure the local air temperature and don’t account for the effects of radiant heat exchange between surfaces and occupants, resulting in suboptimal comfort levels and inefficient energy use.

Finding a way to measure the mean radiant temperature in real time inside buildings could provide a more efficient way of heating the building – leading to more advanced and efficient thermostat controls. Currently, radiant temperature can be measured using either radiometers or black globe sensors. But radiometers are too expensive for commercial use and black globe sensors are slow, bulky and error strewn for many internal environments.

In search of a new approach, first author Fatih Evren (now at Pacific Northwest National Laboratory) and colleagues used low-resolution, low-cost infrared sensors to measure the longwave mean radiant temperature inside buildings. These sensors eliminate the pan/tilt mechanism (where sensors rotate periodically to measure the temperature at different points and an algorithm determines the surface temperature distribution) required by many other sensors used to measure radiative heat. The new optical sensor also requires 4.5 times less computation power than pan/tilt approaches with the same resolution.

Integrating optical sensors to improve room comfort

The researchers tested infrared thermal array sensors with 32 x 32 pixels in four real-world environments (three living spaces and an office) with different room sizes and layouts. They examined three sensor configurations: one sensor on each of the room’s four walls; two sensors; and a single-sensor setup. The sensors measured the mean radiant temperature for 290 h at internal temperatures of between 18 and 26.8 °C.

The optical sensors capture raw 2D thermal data containing temperature information for adjacent walls, floor and ceiling. To determine surface temperature distributions from these raw data, the researchers used projective homographic transformations – a transformation between two different geometric planes. The surfaces of the room were segmented into a homography matrix by marking the corners of the room. Applying the transformations to this matrix provides the surface distribution temperature on each of the surfaces. The surface temperatures can then be used to calculate the mean radiant temperature.

The team compared the temperatures measured by their sensors against ground truth measurements obtained via the net-radiometer method. The optical sensor was found to be repeatable and reliable for different room sizes, layouts and temperature sensing scenarios, with most approaches agreeing within ±0.5 °C of the ground truth measurement, and a maximum error (arising from a single-sensor configuration) of only ±0.96 °C. The optical sensors were also more accurate than the black globe sensor method, which tends to have higher errors due to under/overestimating solar effects.

The researchers conclude that the sensors are repeatable, scalable and predictable, and that they could be integrated into room thermostats to improve human comfort and energy efficiency – especially for controlling the radiant heating and cooling systems now commonly used in high-performance buildings. They also note that a future direction could be to integrate machine learning and other advanced algorithms to improve the calibration of the sensors.

This research was published in Nature Communications.

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A new technique for using frequency combs to measure trace concentrations of gas molecules has been developed by researchers in the US. The team reports single-digit parts-per-trillion detection sensitivity, and extreme broadband coverage over 1000 cm^-1 wavenumbers. This record-level sensing performance could open up a variety of hitherto inaccessible applications in fields such as medicine, environmental chemistry and chemical kinetics.

Each molecular species will absorb light at a specific set of frequencies. So, shining light through a sample of gas and measuring this absorption can reveal the molecular composition of the gas.

Cavity ringdown spectroscopy is an established way to increase the sensitivity of absorption spectroscopy and needs no calibration. A laser is injected between two mirrors, creating an optical standing wave. A sample of gas is then injected into the cavity, so the laser beam passes through it, normally many thousands of times. The absorption of light by the gas is then determined by the rate at which the intracavity light intensity “rings down” – in other words, the rate at which the standing wave decays away.

Researchers have used this method with frequency comb lasers to probe the absorption of gas samples at a range of different light frequencies. A frequency comb produces light at a series of very sharp intensity peaks that are equidistant in frequency – resembling the teeth of a comb.

Shifting resonances

However, the more reflective the mirrors become (the higher the cavity finesse), the narrower each cavity resonance becomes. Due to the fact that their frequencies are not evenly spaced and can be heavily altered by the loaded gas, normally one relies on creating oscillations in the length of the cavity. This creates shifts in all the cavity resonance frequencies to modulate around the comb lines. Multiple resonances are sequentially excited and the transient comb intensity dynamics are captured by a camera, following spatial separation by an optical grating.

“That experimental scheme works in the near-infrared, but not in the mid-infrared,” says Qizhong Liang. “Mid-infrared cameras are not fast enough to capture those dynamics yet.” This is a problem because the mid-infrared is where many molecules can be identified by their unique absorption spectra.

Liang is a member of Jun Ye’s group in JILA in Colorado, which has shown that it is possible to measure transient comb dynamics simply with a Michelson interferometer. The spectrometer entails only beam splitters, a delay stage, and photodetectors. The researchers worked out that, the periodically generated intensity dynamics arising from each tooth of the frequency comb can be detected as a set of Fourier components offset by Doppler frequency shifts. Absorption from the loaded gas can thus be determined.

Dithering the cavity

This process of reading out transient dynamics from “dithering” the cavity by a passive Michelson interferometer is much simpler than previous setups and thus can be used by people with little experience with combs, says Liang. It also places no restrictions on the finesse of the cavity, spectral resolution, or spectral coverage. “If you’re dithering the cavity resonances, then no matter how narrow the cavity resonance is, it’s guaranteed that the comb lines can be deterministically coupled to the cavity resonance twice per cavity round trip modulation,” he explains.

The researchers reported detections of various molecules at concentrations as low as parts-per-billion with parts-per-trillion uncertainty in exhaled air from volunteers. This included biomedically relevant molecules such as acetone, which is a sign of diabetes, and formaldehyde, which is diagnostic of lung cancer. “Detection of molecules in exhaled breath in medicine has been done in the past,” explains Liang. “The more important point here is that, even if you have no prior knowledge about what the gas sample composition is, be it in industrial applications, environmental science applications or whatever you can still use it.”

Konstantin Vodopyanov of the University of Central Florida in Orlando comments: “This achievement is remarkable, as it integrates two cutting-edge techniques: cavity ringdown spectroscopy, where a high-finesse optical cavity dramatically extends the laser beam’s path to enhance sensitivity in detecting weak molecular resonances, and frequency combs, which serve as a precise frequency ruler composed of ultra-sharp spectral lines. By further refining the spectral resolution to the Doppler broadening limit of less than 100 MHz and referencing the absolute frequency scale to a reliable frequency standard, this technology holds great promise for applications such as trace gas detection and medical breath analysis.”

The spectrometer is described in Nature.

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Vacuum technology is routinely used in both scientific research and industrial processes. In physics, high-quality vacuum systems make it possible to study materials under extremely clean and stable conditions. In industry, vacuum is used to lift, position and move objects precisely and reliably. Without these technologies, a great deal of research and development would simply not happen. But for all its advantages, working under vacuum does come with certain challenges. For example, once something is inside a vacuum system, how do you manipulate it without opening the system up?

The UK-based firm UHV Design has been working on this problem for over a quarter of a century, developing and manufacturing vacuum manipulation solutions for new research disciplines as well as emerging industrial applications. Its products, which are based on magnetically coupled linear and rotary probes, are widely used at laboratories around the world, in areas ranging from nanoscience to synchrotron and beamline applications. According to engineering director Jonty Eyres, the firm’s latest innovation – a new sample transfer arm released at the beginning of this year – extends this well-established range into new territory.

“The new product is a magnetically coupled probe that allows you to move a sample from point A to point B in a vacuum system,” Eyres explains. “It was designed to have an order of magnitude improvement in terms of both linear and rotary motion thanks to the magnets in it being arranged in a particular way. It is thus able to move and position objects that are much heavier than was previously possible.”

The new sample arm, Eyres explains, is made up of a vacuum “envelope” comprising a welded flange and tube assembly. This assembly has an outer magnet array that magnetically couples to an inner magnet array attached to an output shaft. The output shaft extends beyond the mounting flange and incorporates a support bearing assembly. “Depending on the model, the shafts can either be in one or more axes: they move samples around either linearly, linear/rotary or incorporating a dual axis to actuate a gripper or equivalent elevating plate,” Eyres says.

Continual development, review and improvement

While similar devices are already on the market, Eyres says that the new product has a significantly larger magnetic coupling strength in terms of its linear thrust and rotary torque. These features were developed in close collaboration with customers who expressed a need for arms that could carry heavier payloads and move them with more precision. In particular, Eyres notes that in the original product, the maximum weight that could be placed on the end of the shaft – a parameter that depends on the stiffness of the shaft as well as the magnetic coupling strength – was too small for these customers’ applications.

“From our point of view, it was not so much the magnetic coupling that needed to be reviewed, but the stiffness of the device in terms of the size of the shaft that extends out to the vacuum system,” Eyres explains. “The new arm deflects much less from its original position even with a heavier load and when moving objects over longer distances.”

The new product – a scaled-up version of the original – can move an object with a mass of up to 50 N (5 kg) over an axial stroke of up to 1.5 m. Eyres notes that it also requires minimal maintenance, which is important for moving higher loads. “It is thus targeted to customers who wish to move larger objects around over longer periods of time without having to worry about intervening too often,” he says.

Moving multiple objects

As well as moving larger, single objects, the new arm’s capabilities make it suitable for moving multiple objects at once. “Rather than having one sample go through at a time, we might want to nest three or four samples onto a large plate, which inevitably increases the size of the overall object,” Eyres explains.

Before they created this product, he continues, he and his UHV Design colleagues were not aware of any magnetic coupled solution on the marketplace that enabled users to do this. “As well as being capable of moving heavy samples, our product can also move lighter samples, but with a lot less shaft deflection over the stroke of the product,” he says. “This could be important for researchers, particularly if they are limited in space or if they wish to avoid adding costly supports in their vacuum system.”

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Researchers at Microsoft in the US claim to have made the first topological quantum bit (qubit) – a potentially transformative device that could make quantum computing robust against the errors that currently restrict what it can achieve. “If the claim stands, it would be a scientific milestone for the field of topological quantum computing and physics beyond,” says Scott Aaronson, a computer scientist at the University of Texas at Austin.

However, the claim is controversial because the evidence supporting it has not yet been presented in a peer-reviewed paper. It is made in a press release from Microsoft accompanying a paper in Nature (638 651) that has been written by more than 160 researchers from the company’s Azure Quantum team. The paper stops short of claiming a topological qubit but instead reports some of the key device characterization underpinning it.

Writing in a peer-review file accompanying the paper, the Nature editorial team says that it sought additional input from two of the article’s reviewers to “establish its technical correctness”, concluding that “the results in this manuscript do not represent evidence for the presence of Majorana zero modes [MZMs] in the reported devices”. An MZM is a quasiparticle (a particle-like collective electronic state) that can act as a topological qubit.

“That’s a big no-no”

“The peer-reviewed publication is quite clear [that it contains] no proof for topological qubits,” says Winfried Hensinger, a physicist at the University of Sussex who works on quantum computing using trapped ions. “But the press release speaks differently. In academia that’s a big no-no: you shouldn’t make claims that are not supported by a peer-reviewed publication” – or that have at least been presented in a preprint.

Chetan Nayak, leader of Microsoft Azure Quantum, which is based in Redmond, Washington, says that the evidence for a topological qubit was obtained in the period between submission of the paper in March 2024 and its publication. He will present those results at a talk at the Global Physics Summit of the American Physical Society in Anaheim in March.

But Hensinger is concerned that “the press release doesn’t make it clear what the paper does and doesn’t contain”. He worries that some might conclude that the strong claim of having made a topological qubit is now supported by a paper in Nature. “We don’t need to make these claims – that is just unhealthy and will really hurt the field,” he says, because it could lead to unrealistic expectations about what quantum computers can do.

As with the qubits used in current quantum computers, such as superconducting components or trapped ions, MZMs would be able to encode superpositions of the two readout states (representing a 1 or 0). By quantum-entangling such qubits, information could be manipulated in ways not possible for classical computers, greatly speeding up certain kinds of computation. In MZMs the two states are distinguished by “parity”: whether the quasiparticles contain even or odd numbers of electrons.

Built-in error protection

As MZMs are “topological” states, their settings cannot easily be flipped by random fluctuations to introduce errors into the calculation. Rather, the states are like a twist in a buckled belt that cannot be smoothed out unless the buckle is undone. Topological qubits would therefore suffer far less from the errors that afflict current quantum computers, and which limit the scale of the computations they can support. Because quantum error correction is one of the most challenging issues for scaling up quantum computers, “we want some built-in level of error protection”, explains Nayak.

It has long been thought that MZMs might be produced at the ends of nanoscale wires made of a superconducting material. Indeed, Microsoft researchers have been trying for several years to fabricate such structures and look for the characteristic signature of MZMs at their tips. But it can be hard to distinguish this signature from those of other electronic states that can form in these structures.

In 2018 researchers at labs in the US and the Netherlands (including the Delft University of Technology and Microsoft), claimed to have evidence of an MZM in such devices. However, they then had to retract the work after others raised problems with the data. “That history is making some experts cautious about the new claim,” says Aaronson.

Now, though, it seems that Nayak and colleagues have cracked the technical challenges. In the Nature paper, they report measurements in a nanowire heterostructure made of superconducting aluminium and semiconducting indium arsenide that are consistent with, but not definitive proof of, MZMs forming at the two ends. The crucial advance is an ability to accurately measure the parity of the electronic states. “The paper shows that we can do these measurements fast and accurately,” says Nayak.

The device is a remarkable achievement from the materials science and fabrication standpoint

Ivar Martin, Argonne National Laboratory

“The device is a remarkable achievement from the materials science and fabrication standpoint,” says Ivar Martin, a materials scientist at Argonne National Laboratory in the US. “They have been working hard on these problems, and seems like they are nearing getting the complexities under control.” In the press release, the Microsoft team claims now to have put eight MZM topological qubits on a chip called Majorana 1, which is designed to house a million of them (see figure).

Even if the Microsoft claim stands up, a lot will still need to be done to get from a single MZM to a quantum computer, says Hensinger. Topological quantum computing is “probably 20–30 years behind the other platforms”, he says. Martin agrees. “Even if everything checks out and what they have realized are MZMs, cleaning them up to take full advantage of topological protection will still require significant effort,” he says.

Regardless of the debate about the results and how they have been announced, researchers are supportive of the efforts at Microsoft to produce a topological quantum computer. “As a scientist who likes to see things tried, I’m grateful that at least one player stuck with the topological approach even when it ended up being a long, painful slog,” says Aaronson.

“Most governments won’t fund such work, because it’s way too risky and expensive,” adds Hensinger. “So it’s very nice to see that Microsoft is stepping in there.”

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Solid-state batteries are considered next-generation energy storage technology as they promise higher energy density and safety than lithium-ion batteries with a liquid electrolyte. However, major obstacles for commercialization are the requirement of high stack pressures as well as insufficient power density. Both aspects are closely related to limitations of charge transport within the composite cathode.

This webinar presents an introduction on how to use electrochemical impedance spectroscopy for the investigation of composite cathode microstructures to identify kinetic bottlenecks. Effective conductivities can be obtained using transmission line models and be used to evaluate the main factors limiting electronic and ionic charge transport.

In combination with high-resolution 3D imaging techniques and electrochemical cell cycling, the crucial role of the cathode microstructure can be revealed, relevant factors influencing the cathode performance identified, and optimization strategies for improved cathode performance.

Philip Minnmann received his M.Sc. in Material from RWTH Aachen University. He later joined Prof. Jürgen Janek’s group at JLU Giessen as part of the BMBF Cluster of Competence for Solid-State Batteries FestBatt. During his Ph.D., he worked on composite cathode characterization for sulfide-based solid-state batteries, as well as processing scalable, slurry-based solid-state batteries. Since 2023, he has been a project manager for high-throughput battery material research at HTE GmbH.

 

Johannes Schubert holds an M.Sc. in Material Science from the Justus-Liebig University Giessen, Germany. He is currently a Ph.D. student in the research group of Prof. Jürgen Janek in Giessen, where he is part of the BMBF Competence Cluster for Solid-State Batteries FestBatt. His main research focuses on characterization and optimization of composite cathodes with sulfide-based solid electrolytes.

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Fusion – the process that powers the Sun – offers a tantalizing opportunity to generate almost unlimited amounts of clean energy. In the Sun’s core, matter is more than 10 times denser than lead and temperatures reach 15 million K. In these conditions, ionized isotopes of hydrogen (deuterium and tritium) can overcome their electrostatic repulsion, fusing into helium nuclei and ejecting high-energy neutrons. The products of this reaction are slightly lighter than the two reacting nuclei, and the excess mass is converted to lots of energy.

The engineering and materials challenges of creating what is essentially a ‘Sun in a freezer’ are formidable

The Sun’s core is kept hot and dense by the enormous gravitational force exerted by its huge mass. To achieve nuclear fusion on Earth, different tactics are needed. Instead of gravity, the most common approach uses strong superconducting magnets operating at ultracold temperatures to confine the intensely hot hydrogen plasma.

The engineering and materials challenges of creating what is essentially a “Sun in a freezer”, and harnessing its power to make electricity, are formidable. This is partly because, over time, high-energy neutrons from the fusion reaction will damage the surrounding materials. Superconductors are incredibly sensitive to this kind of damage, so substantial shielding is needed to maximize the lifetime of the reactor.

The traditional roadmap towards fusion power, led by large international projects, has set its sights on bigger and bigger reactors, at greater and greater expense. However these are moving at a snail’s pace, with the first power to the grid not anticipated until the 2060s, leading to the common perception that “fusion power is 30 years away, and always will be.”

There is therefore considerable interest in alternative concepts for smaller, simpler reactors to speed up the fusion timeline. Such novel reactors will need a different toolkit of superconductors. Promising materials exist, but because fusion can still only be sustained in brief bursts, we have no way to directly test how these compounds will degrade over decades of use.

Is smaller better?

A leading concept for a nuclear fusion reactor is a machine called a tokamak, in which the plasma is confined to a doughnut-shaped region. In a tokamak, D-shaped electromagnets are arranged in a ring around a central column, producing a circulating (toroidal) magnetic field. This exerts a force (the Lorentz force) on the positively charged hydrogen nuclei, making them trace helical paths that follow the field lines and keep them away from the walls of the vessel.

In 2010, construction began in France on ITER, a tokamak that is designed to demonstrate the viability of nuclear fusion for energy generation. The aim is to produce burning plasma, where more than half of the energy heating the plasma comes from fusion in the plasma itself, and to generate, for short pulses, a tenfold return on the power input.

But despite being proposed 40 years ago, ITER’s projected first operation was recently pushed back by another 10 years to 2034. The project’s budget has also been revised multiple times and it is currently expected to cost tens of billions of euros. One reason ITER is such an ambitious and costly project is its sheer size. ITER’s plasma radius of 6.2 m is twice that of the JT-60SA in Japan, the world’s current largest tokamak. The power generated by a tokamak roughly scales with the radius of the doughnut cubed which means that doubling the radius should yield an eight-fold increase in power.

However, instead of chasing larger and larger tokamaks, some organizations are going in the opposite direction. Private companies like Tokamak Energy in the UK and Commonwealth Fusion Systems in the US are developing compact tokamaks that, they hope, could bring fusion power to the grid in the 2030s. Their approach is to ramp up the magnetic field rather than the size of the tokamak. The fusion power of a tokamak has a stronger dependence on the magnetic field than the radius, scaling with the fourth power.

The drawback of smaller tokamaks is that the materials will sustain more damage from neutrons during operation. Of all the materials in the tokamak, the superconducting magnets are most sensitive to this. If the reactor is made more compact, they are also closer to the plasma and there will be less space for shielding. So if compact tokamaks are to succeed commercially, we need to choose superconducting materials that will be functional even after many years of irradiation.

High-performance fusion materials

Superconductors are a class of materials that, when cooled below a characteristic temperature, conduct with no resistance (see box 1, above). Magnets made from superconducting wires can carry high currents without overheating, making them ideal for generating the very high fields required for fusion. Superconductivity is highly sensitive to the arrangement of the atoms; whilst some amorphous superconductors exist, most superconducting compounds only conduct high currents in a specific crystalline state. A few defects will always arise, and can sometimes even improve the material’s performance. But introducing significant disorder to a crystalline superconductor will eventually destroy its ability to superconduct.

The most common material for superconducting magnets is a niobium-titanium (Nb-Ti) alloy, which is used in MRI machines in hospitals and CERN’s Large Hadron Collider. Nb-Ti superconducting magnets are relatively cheap and easy to manufacture, but – like all superconducting materials – it has an upper limit to the magnetic field in which it can superconduct, known as the irreversibility field. This value in Nb-Ti is too low for this material to be used for the high-field magnets in ITER. The ITER tokamak will instead use a niobium-tin (Nb₃Sn) superconductor, which has a higher irreversibility field than Nb-Ti, even though it is much more expensive and challenging to work with.

Needing stronger magnetic fields, compact tokamaks require a superconducting material with an even higher irreversibility field. Over the last decade, another class of superconducting materials called “REBCO” have been proposed as an alternative. Short for rare earth barium copper oxide, these are a family of superconductors with the chemical formula REBa₂Cu₃O₇, where RE is a rare-earth element such as yttrium, gadolinium or europium (see Box 2 “REBCO unit cell”).

REBCO compounds  are high-temperature superconductors, which are defined as having transition temperatures above 77 K, meaning they can be cooled with liquid nitrogen rather than the more expensive liquid helium. REBCO compounds also have a much higher irreversibility field than niobium-tin, and so can sustain the high fields necessary for a small fusion reactor.

REBCO wires: Bendy but brittle

REBCO materials have attractive superconducting properties, but it is not easy to manufacture them into flexible wires for electromagnets. REBCO is a brittle ceramic so can’t be made into wires in the same way as ductile materials like copper or Nb-Ti, where the material is drawn through progressively smaller holes.

Instead, REBCO tapes are manufactured by coating metallic ribbons with a series of very thin ceramic layers, one of which is the superconducting REBCO compound. Ideally, the REBCO would be a single crystal, but in practice, it will be comprised of many small grains. The metal gives mechanical stability and flexibility whilst the underlying ceramic “buffer” layers protect the REBCO from chemical reactions with the metal and act as a template for aligning the REBCO grains. This is important because the boundaries between individual grains reduce the maximum current the wire can carry.

Another potential problem is that these compounds are chemically sensitive and are “poisoned” by nearly all the impurities that may be introduced during manufacture. These impurities can produce insulating compounds that block supercurrent flow or degrade the performance of the REBCO compound itself.

Despite these challenges, and thanks to impressive materials engineering from several companies and institutions worldwide, REBCO is now made in kilometre-long, flexible tapes capable of carrying thousands of amps of current. In 2024, more than 10,000 km of this material was manufactured for the burgeoning fusion industry. This is impressive given that only 1000 km was made in  2020. However, a single compact tokamak will require up to 20,000 km of this REBCO-coated conductor for the magnet systems, and because the superconductor is so expensive to manufacture it is estimated that this would account for a considerable fraction of the total cost of a power plant.

Pushing superconductors to the limit

Another problem with REBCO materials is that the temperature below which they superconduct falls steeply once they’ve been irradiated with neutrons. Their lifetime in service will depend on the reactor design and amount of shielding, but research from the Vienna University of Technology in 2018 suggested that REBCO materials can withstand about a thousand times less damage than structural materials like steel before they start to lose performance (Supercond. Sci. Technol. 31 044006).

These experiments are currently being used by the designers of small fusion machines to assess how much shielding will be required, but they don’t tell the whole story. The 2018 study used neutrons from a fission reactor, which have a different spectrum of energies compared to fusion neutrons. They also did not reproduce the environment inside a compact tokamak, where the superconducting tapes will be at cryogenic temperatures, carrying high currents and under considerable strain from Lorentz forces generated in the magnets.

Even if we could get a sample of REBCO inside a working tokamak, the maximum runtime of current machines is measured in minutes, meaning we cannot do enough damage to test how susceptible the superconductor will be in a real fusion environment. The current record for tokamak power is 69 megajoules, achieved in a 5-second burst at the Joint European Torus (JET) tokamak in the UK.

Given the difficulty of using neutrons from fusion reactors, our team is looking for answers using ions instead. Ion irradiation is much more readily available, quicker to perform, and doesn’t make the samples radioactive. It is also possible to access a wide range of energies and ion species to tune the damage mechanisms in the material. The trouble is that because ions are charged they won’t interact with materials in exactly the same way as neutrons, so it is not clear if these particles cause the same kinds of damage or by the same mechanisms.

To find out, we first tried to directly image the crystalline structure of REBCO after both neutron and ion irradiation using transmission electron microscopy (TEM). When we compared the samples, we saw small amorphous regions in the neutron-irradiated REBCO where the crystal structure was destroyed (J. Microsc. 286 3), which are not observed after light ion irradiation (see Box 3 below).

We believe these regions to be collision cascades generated initially by a single violent neutron impact that knocks an atom out of its place in the lattice with enough energy that the atom ricochets through the material, knocking other atoms from their positions. However, these amorphous regions are small, and superconducting currents should be able to pass around them, so it was likely that another effect was reducing the superconducting transition temperature.

Searching for clues

The TEM images didn’t show any other defects, so on our hunt to understand the effect of neutron irradiation, we instead thought about what we couldn’t see in the images. The TEM technique we used cannot resolve the oxygen atoms in REBCO because they are too light to scatter the electrons by large angles. Oxygen is also the most mobile atom in a REBCO material, which led us to think that oxygen point defects – single oxygen atoms that have been moved out of place and which are distributed randomly throughout the material – might be responsible for the drop in transition temperature.

In REBCO, the oxygen atoms are all bonded to copper, so the bonding environment of the copper atoms can be used to identify oxygen defects. To test this theory we switched from electrons to photons, using a technique called X-ray absorption spectroscopy. Here the sample is illuminated with X-rays that preferentially excite the copper atoms; the precise energies where absorption is highest indicate specific bonding arrangements, and therefore point to specific defects. We have started to identify the defects that are likely to be present in the irradiated samples, finding spectral changes that are consistent with oxygen atoms moving into unoccupied sites (Communications Materials 3 52).

We see very similar changes to the spectra when we irradiate with helium ions and neutrons, suggesting that similar defects are created in both cases (Supercond. Sci. Technol. 36 10LT01 ). This work has increased our confidence that light ions are a good proxy for neutron damage in REBCO superconductors, and that this damage is due to changes in the oxygen lattice.

Another advantage of ion irradiation is that, compared to neutrons, it is easier to access experimentally relevant cryogenic temperatures. Our experiments are performed at the Surrey Ion Beam Centre, where a cryocooler can be attached to the end of the ion accelerator, enabling us to recreate some of the conditions inside a fusion reactor.

We have shown that when REBCO is irradiated at cryogenic temperatures and then allowed to warm to room temperature, it recovers some of its superconducting properties (Supercond. Sci. Technol. 34 09LT01). We attribute this to annealing, where rearrangements of atoms occur in a material warmed below its melting point, smoothing out defects in the crystal lattice. We have shown that further recovery of a perfect superconducting lattice can be induced using careful heat treatments to avoid loss of oxygen from the samples (MRS Bulletin 48 710).

Lots more experiments are required to fully understand the effect of irradiation temperature on the degradation of REBCO. Our results indicate that room temperature and cryogenic irradiation with helium ions lead to a similar rate of degradation, but similar work by a group at the Massachusetts Institute of Technology (MIT) in the US using proton irradiation has found that the superconductor degrades more rapidly at cryogenic temperatures (Rev. Sci. Instrum. 95 063907).  The effect of other critical parameters like magnetic field and strain also still needs to be explored.

Towards net zero

The remarkable properties of REBCO high-temperature superconductors present new opportunities for designing fusion reactors that are substantially smaller (and cheaper) than traditional tokamaks, and which private companies ambitiously promise will enable the delivery of power to the grid on vastly accelerated timescales. REBCO tape can already be manufactured commercially with the required performance but more research is needed to understand the effects of neutron damage that the magnets will be subjected to so they will achieve the desired service lifetimes.

This would open up extensive new applications, such as lossless transmission cables, wind turbine generators and magnet-based energy storage devices

Scale-up of REBCO tape production is already happening at pace, and it is expected that this will drive down the cost of manufacture. This would open up extensive new applications, not only in fusion but also in power applications such as lossless transmission cables, for which the historically high costs of the superconducting material have proved prohibitive. Superconductors are also being introduced into wind turbine generators, and magnet-based energy storage devices.

This symbiotic relationship between fusion and superconductor research could lead not only to the realization of clean fusion energy but also many other superconducting technologies that will contribute to the achievement of net zero.

The post The quest for better fusion reactors is putting a new generation of superconductors to the test appeared first on Physics World.

Join us for an insightful webinar that delves into the role of Cobalt-60 in intracranial radiosurgery using Leksell Gamma Knife.

Through detailed discussions and expert insights, attendees will learn how Leksell Gamma Knife, powered by cobalt-60, has and continues to revolutionize the field of radiosurgery, offering patients a safe and effective treatment option.

Participants will gain a comprehensive understanding of the use of cobalt in medical applications, highlighting its significance, and learn more about the unique properties of cobalt-60. The webinar will explore the benefits of cobalt-60 in intracranial radiosurgery and why it is an ideal choice for treating brain lesions while minimizing damage to surrounding healthy tissue.

Don’t miss this opportunity to enhance your knowledge and stay at the forefront of medical advancements in radiosurgery!

Riccardo Bevilacqua, a nuclear physicist with a PhD in neutron data for Generation IV nuclear reactors from Uppsala University, has worked as a scientist for the European Commission and at various international research facilities. His career has transitioned from research to radiation safety and back to medical physics, the field that first interested him as a student in Italy. Based in Stockholm, Sweden, he leads global radiation safety initiatives at Elekta. Outside of work, Riccardo is a father, a stepfather, and writes popular science articles on physics and radiation.

 

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Physicists in Austria have shown that the static electricity acquired by identical material samples can evolve differently over time, based on each samples’ history of contact with other samples. Led by Juan Carlos Sobarzo and Scott Waitukaitis at the Institute of Science and Technology Austria, the team hope that their experimental results could provide new insights into one of the oldest mysteries in physics.

Static electricity – also known as contact electrification or triboelectrification — has been studied for centuries. However, physicists still do not understand some aspects of how it works.

“It’s a seemingly simple effect,” Sobarzo explains. “Take two materials, make them touch and separate them, and they will have exchanged electric charge. Yet, the experiments are plagued by unpredictability.”

This mystery is epitomized by an early experiment carried out by the German-Swedish physicist Johan Wilcke in 1757. When glass was touched to paper, Wilcke found that glass gained a positive charge – while when paper was touched to sulphur, it would itself become positively charged.

Triboelectric series

Wilcke concluded that glass will become positively charged when touched to sulphur. This concept formed the basis of the triboelectric series, which ranks materials according to the charge they acquire when touched to another material.

Yet in the intervening centuries, the triboelectric series has proven to be notoriously inconsistent. Despite our vastly improved knowledge of material properties since the time of Wilcke’s experiments, even the latest attempts at ordering materials into triboelectric series have repeatedly failed to hold up to experimental scrutiny.

According to Sobarzo’s and colleagues, this problem has been confounded by the diverse array of variables associated with a material’s contact electrification. These include its electronic properties, pH, hydrophobicity, and mechanochemistry, to name just a few.

In their new study, the team approached the problem from a new perspective. “In order to reduce the number of variables, we decided to use identical materials,” Sobarzo describes. “Our samples are made of a soft polymer (PDMS) that I fabricate myself in the lab, cut from a single piece of material.”

Starting from scratch

For these identical materials, the team proposed that triboelectric properties could evolve over time as the samples were brought into contact with other, initially identical samples. If this were the case, it would allow the team to build a triboelectric series from scratch.

At first, the results seemed as unpredictable as ever. However, as the same set of samples underwent repeated contacts, the team found that their charging behaviour became more consistent, gradually forming a clear triboelectric series.

Initially, the researchers attempted to uncover correlations between this evolution and variations in the parameters of each sample – with no conclusive results. This led them to consider whether the triboelectric behaviour of each sample was affected by the act of contact itself.

Contact history

“Once we started to keep track of the contact history of our samples – that is, the number of times each sample has been contacted to others–the unpredictability we saw initially started to make sense,” Sobarzo explains. “The more contacts samples would have in their history, the more predictable they would behave. Not only that, but a sample with more contacts in its history will consistently charge negative against a sample with less contacts in its history.”

To explain the origins of this history-dependent behaviour, the team used a variety of techniques to analyse differences between the surfaces of uncontacted samples, and those which had already been contacted several times. Their measurements revealed just one difference between samples at different positions on the triboelectric series. This was their nanoscale surface roughness, which smoothed out as the samples experienced more contacts.

“I think the main take away is the importance of contact history and how it can subvert the widespread unpredictability observed in tribocharging,” Sobarzo says. “Contact is necessary for the effect to happen, it’s part of the name ‘contact electrification’, and yet it’s been widely overlooked.”

The team is still uncertain of how surface roughness could be affecting their samples’ place within the triboelectric series. However, their results could now provide the first steps towards a comprehensive model that can predict a material’s triboelectric properties based on its contact-induced surface roughness.

Sobarzo and colleagues are hopeful that such a model could enable robust methods for predicting the charges which any given pair of materials will acquire as they touch each other and separate. In turn, it may finally help to provide a solution to one of the most long-standing mysteries in physics.

The research is described in Nature.

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A photothermal, nanoparticle-based deep brain stimulation (DBS) system has successfully reversed the symptoms of Parkinson’s disease in laboratory mice. Under development by researchers in Beijing, China, the injectable, wireless DBS not only reversed neuron degeneration, but also boosted dopamine levels by clearing out the buildup of harmful fibrils around dopamine neurons. Following DBS treatment, diseased mice exhibited near comparable locomotive behaviour to that of healthy control mice.

Parkinson’s disease is a chronic brain disorder characterized by the degeneration of dopamine-producing neurons and the subsequent loss of dopamine in regions of the brain. Current DBS treatments focus on amplifying dopamine signalling and production, and may require permanent implantation of electrodes in the brain. Another approach under investigation is optogenetics, which involves gene modification. Both techniques increase dopamine levels and reduce Parkinsonian motor symptoms, but they do not restore degenerated neurons to stop disease progression.

The research team, at the National Center for Nanoscience and Technology of the Chinese Academy of Sciences, hypothesized that the heat-sensitive receptor TRPV1, which is highly expressed in dopamine neurons, could serve as a modulatory target to activate dopamine neurons in the substantia nigra of the midbrain. This region contains a large concentration of dopamine neurons and plays a crucial role in how the brain controls bodily movement.

Previous studies have shown that neuron degeneration is mainly driven by α-synuclein (α-syn) fibrils aggregating in the substantia nigra. Successful treatment, therefore, relies on removing this build up, which requires restarting of the intracellular autophagic process (in which a cell breaks down and removes unnecessary or dysfunctional components).

As such, principal investigator Chunying Chen and colleagues aimed to develop a therapeutic system that could reduce α-syn accumulation by simultaneously disaggregating α-syn fibrils and initiating the autophagic process. Their three-component DBS nanosystem, named ATB (Au@TRPV1@β-syn), combines photothermal gold nanoparticles, dopamine neuron-activating TRPV1 antibodies, and β-synuclein (β-syn) peptides that break down α-syn fibrils.

The ATB nanoparticles anchor to dopamine neurons through the TRPV1 receptor then, acting as nanoantennae, convert pulsed near-infrared (NIR) irradiation into heat. This activates the heat-sensitive TRPV1 receptor and restores degenerated dopamine neurons. At the same time, the nanoparticles release β-syn peptides that clear out α-syn fibril buildup and stimulate intracellular autophagy.

The researchers first tested the system in vitro in cellular models of Parkinson’s disease. They verified that under NIR laser irradiation, ATB nanoparticles activate neurons through photothermal stimulation by acting on the TRPV1 receptor, and that the nanoparticles successfully counteracted the α-syn preformed fibril (PFF)-induced death of dopamine neurons. In cell viability assays, neuron death was reduced from 68% to zero following ATB nanoparticle treatment.

Next, Chen and colleagues investigated mice with PFF-induced Parkinson’s disease. The DBS treatment begins with stereotactic injection of the ATB nanoparticles directly into the substantia nigra. They selected this approach over systemic administration because it provides precise targeting, avoids the blood–brain barrier and achieves a high local nanoparticle concentration with a low dose – potentially boosting treatment effectiveness.

Following injection of either nanoparticles or saline, the mice underwent pulsed NIR irradiation once a week for five weeks. The team then performed a series of tests to assess the animals’ motor abilities (after a week of training), comparing the performance of treated and untreated PFF mice, as well as healthy control mice. This included the rotarod test, which measures the time until the animal falls from a rotating rod that accelerates from 5 to 50 rpm over 5 min, and the pole test, which records the time for mice to crawl down a 75 cm-long pole.

The team also performed an open field test to evaluate locomotive activity and exploratory behaviour. Here, mice are free to move around a 50 x 50 cm area, while their movement paths and the number of times they cross a central square are recorded. In all tests, mice treated with nanoparticles and irradiation significantly outperformed untreated controls, with near comparable performance to that of healthy mice.

Visualizing the dopamine neurons via immunohistochemistry revealed a reduction in neurons in PFF-treated mice compared with controls. This loss was reversed following nanoparticle treatment. Safety assessments determined that the treatment did not cause biochemical toxicity and that the heat generated by the NIR-irradiated ATB nanoparticles did not cause any considerable damage to the dopamine neurons.

Eight weeks after treatment, none of the mice experienced any toxicities. The ATB nanoparticles remained stable in the substantia nigra, with only a few particles migrating to cerebrospinal fluid. The researchers also report that the particles did not migrate to the heart, liver, spleen, lung or kidney and were not found in blood, urine or faeces.

Chen tells Physics World that having discovered the neuroprotective properties of gold clusters in Parkinson’s disease models, the researchers are now investigating therapeutic strategies based on gold clusters. Their current research focuses on engineering multifunctional gold cluster nanocomposites capable of simultaneously targeting α-syn aggregation, mitigating oxidative stress and promoting dopamine neuron regeneration.

The study is reported in Science Advances.

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For the first time, inverse design has been used to engineer specific functionalities into a universal spin-wave-based device. It was created by Andrii Chumak and colleagues at Austria’s University of Vienna, who hope that their magnonic device could pave the way for substantial improvements to the energy efficiency of data processing techniques.

Inverse design is a fast-growing technique for developing new materials and devices that are specialized for highly specific uses. Starting from a desired functionality, inverse-design algorithms work backwards to find the best system or structure to achieve that functionality.

“Inverse design has a lot of potential because all we have to do is create a highly reconfigurable medium, and give it control over a computer,” Chumak explains. “It will use algorithms to get any functionality we want with the same device.”

One area where inverse design could be useful is creating systems for encoding and processing data using quantized spin waves called magnons. These quasiparticles are collective excitations that propagate in magnetic materials. Information can be encoded in the amplitude, phase, and frequency of magnons – which interact with radio-frequency (RF) signals.

Collective rotation

A magnon propagates by the collective rotation of stationary spins (no particles move) so it offers a highly energy-efficient way to transfer and process information. So far, however, such magnonics has been limited by existing approaches to the design of RF devices.

“Usually we use direct design – where we know how the spin waves behave in each component, and put the components together to get a working device,” Chumak explains. “But this sometimes takes years, and only works for one functionality.”

Recently, two theoretical studies considered how inverse design could be used to create magnonic devices. These took the physics of magnetic materials as a starting point to engineer a neural-network device.

Building on these results, Chumak’s team set out to show how that approach could be realized in the lab using a 7×7 array of independently-controlled current loops, each generating a small magnetic field.

Thin magnetic film

The team attached the array to a thin magnetic film of yttrium iron garnet. As RF spin waves propagated through the film, differences in the strengths of magnetic fields generated by the loops induced a variety of effects: including phase shifts, interference, and scattering. This in turn created complex patterns that could be tuned in real time by adjusting the current in each individual loop.

To make these adjustments, the researchers developed a pair of feedback-loop algorithms. These took a desired functionality as an input, and iteratively adjusted the current in each loop to optimize the spin wave propagation in the film for specific tasks.

This approach enabled them to engineer two specific signal-processing functionalities in their device. These are a notch filter, which blocks a specific range of frequencies while allowing others to pass through; and a demultiplexer, which separates a combined signal into its distinct component signals. “These RF applications could potentially be used for applications including cellular communications, WiFi, and GPS,” says Chumak.

While the device is a success in terms of functionality, it has several drawbacks, explains Chumak. “The demonstrator is big and consumes a lot of energy, but it was important to understand whether this idea works or not. And we proved that it did.”

Through their future research, the team will now aim to reduce these energy requirements, and will also explore how inverse design could be applied more universally – perhaps paving the way for ultra-efficient magnonic logic gates.

The research is described in Nature Electronics.

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A tense particle-physics showdown will reach new heights in 2025. Over the past 25 years researchers have seen a persistent and growing discrepancy between the theoretical predictions and experimental measurements of an inherent property of the muon – its anomalous magnetic moment. Known as the “muon g-2”, this property serves as a robust test of our understanding of particle physics.

Theoretical predictions of the muon g-2 are based on the Standard Model of particle physics (SM). This is our current best theory of fundamental forces and particles, but it does not agree with everything observed in the universe. While the tensions between g-2 theory and experiment have challenged the foundations of particle physics and potentially offer a tantalizing glimpse of new physics beyond the SM, it turns out that there is more than one way to make SM predictions.

In recent years, a new SM prediction of the muon g-2 has emerged that questions whether the discrepancy exists at all, suggesting that there is no new physics in the muon g-2. For the particle-physics community, the stakes are higher than ever.

Rising to the occasion?

To understand how this discrepancy in the value of the muon g-2 arises, imagine you’re baking some cupcakes. A well-known and trusted recipe tells you that by accurately weighing the ingredients using your kitchen scales you will make enough batter to give you 10 identical cupcakes of a given size. However, to your surprise, after portioning out the batter, you end up with 11 cakes of the expected size instead of 10.

What has happened? Maybe your scales are imprecise. You check and find that you’re confident that your measurements are accurate to 1%. This means each of your 10 cupcakes could be 1% larger than they should be, or you could have enough leftover mixture to make 1/10th of an extra cupcake, but there’s no way you should have a whole extra cupcake.

You repeat the process several times, always with the same outcome. The recipe clearly states that you should have batter for 10 cupcakes, but you always end up with 11. Not only do you now have a worrying number of cupcakes to eat but, thanks to all your repeated experiments, you’re more confident that you are following all the steps and measurements accurately. You start to wonder whether something is missing from the recipe itself.

Before you jump to conclusions, it’s worth checking that there isn’t something systematically wrong with your scales. You ask several friends to follow the same recipe using their own scales. Amazingly, when each friend follows the recipe, they all end up with 11 cupcakes. You are more sure than ever that the cupcake recipe isn’t quite right.

You’re really excited now, as you have corroborating evidence that something is amiss. This is unprecedented, as the recipe is considered sacrosanct. Cupcakes have never been made differently and if this recipe is incomplete there could be other, larger implications. What if all cake recipes are incomplete? These claims are causing a stir, and people are starting to take notice.

Then, a new friend comes along and explains that they checked the recipe by simulating baking the cupcakes using a computer. This approach doesn’t need physical scales, but it uses the same recipe. To your shock, the simulation produces 11 cupcakes of the expected size, with a precision as good as when you baked them for real.

There is no explaining this. You were certain that the recipe was missing something crucial, but now a computer simulation is telling you that the recipe has always predicted 11 cupcakes.

Of course, one extra cupcake isn’t going to change the world. But what if instead of cake, the recipe was particle physics’ best and most-tested theory of everything, and the ingredients were the known particles and forces? And what if the number of cupcakes was a measurable outcome of those particles interacting, one hurtling towards a pivotal bake-off between theory and experiment?

What is the muon g-2?

Muons are an elementary particle in the SM that have a half-integer spin, and are similar to electrons, but are some 207 times heavier. Muons interact directly with other SM particles via electromagnetism (photons) and the weak force (W and Z bosons, and the Higgs particle). All quarks and leptons – such as electrons and muons – have a magnetic moment due to their intrinsic angular momentum or “spin”. Quantum theory dictates that the magnetic moment is related to the spin by a quantity known as the “g-factor”. Initially, this value was predicted to be at g = 2 for both the electron and the muon.

However, these calculations did not take into account the effects of “radiative corrections” – the continuous emission and re-absorption of short-lived “virtual particles” (see box) by the electron or muon – which increases g by about 0.1%. This seemingly minute difference is referred to as “anomalous g-factor”, a_µ = (g – 2)/2. As well as the electromagnetic and weak interactions, the muon’s magnetic moment also receives contributions from the strong force, even though the muon does not itself participate in strong interactions. The strong contributions arise through the muon’s interaction with the photon, which in turn interacts with quarks. The quarks then themselves interact via the strong-force mediator, the gluon.

This effect, and any discrepancies, are of particular interest to physicists because the g-factor acts as a probe of the existence of other particles – both known particles such as electrons and photons, and other, as yet undiscovered, particles that are not part of the SM.

The muon, the (lighter) electron and the (heavier) tau lepton all have an anomalous magnetic moment.  However, because the muon is heavier than the electron, the impact of heavy new particles on the muon g-2 is amplified. While tau leptons are even heavier than muons, tau leptons are extremely short-lived (muons have a lifetime of 2.2 μs, while the lifetime of tau leptons is 0.29 ns), making measurements impracticable with current technologies. Neither too light nor too heavy, the muon is the perfect tool to search for new physics.

New physics beyond the Standard Model (commonly known as BSM physics) is sorely needed because, despite its many successes, the SM does not provide the answers to all that we observe in the universe, such as the existence of dark matter. “We know there is something beyond the predictions of the Standard Model, we just don’t know where,” says Patrick Koppenburg, a physicist at the Dutch National Institute for Subatomic Physics (Nikhef) in the Netherlands, who works on the LHCb Experiment at CERN and on future collider experiments. “This new physics will provide new particles that we haven’t observed yet. The LHC collider experiments are actively searching for such particles but haven’t found anything to date.”

Testing the Standard Model: experiment vs theory

In 2021 the Muon g-2 experiment at Fermilab in the US captured the world’s attention with the release of its first result (Phys. Rev. Lett. 126 141801). It had directly measured the muon g-2 to an unprecedented precision of 460 parts per billion (ppb). While the LHC experiments attempt to produce and detect BSM particles directly, the Muon g-2 experiment takes a different, complementary approach – it compares precision measurements of particles with SM predictions to expose discrepancies that could be due to new physics. In the Muon g-2 experiment, muons travel round and round a circular ring, confined by a strong magnetic field. In this field, the muons precess like spinning tops (see image at the top of this article). The frequency of this precession is the anomalous magnetic moment and it can be extracted by detecting where and when the muons decay.

Having led the experiment as manager and run co-ordinator, Muon g-2 is an awe-inspiring feature of science and engineering, involving more than 200 scientists from 35 institutions in seven countries. I have been involved in both the operation of the experiment and the analysis of results. “A lot of my favourite memories from g-2 are ‘firsts’,” says Saskia Charity, a researcher at the University of Liverpool in the UK and a principal analyser of the Muon g-2 experiment’s results. “The first time we powered the magnet; the first time we stored muons and saw particles in the detectors; and the first time we released a result in 2021.”

The Muon g-2 result turned heads because the measured value was significantly higher than the best SM prediction (at that time) of the muon g-2 (Phys. Rep. 887 1). This SM prediction was the culmination of years of collaborative work by the Muon g-2 Theory Initiative, an international consortium of roughly 200 theoretical physicists (myself among them). In 2020 the collaboration published one community-approved number for the muon g-2. This value had a precision comparable to the Fermilab experiment – resulting in a deviation between the two that has a chance of 1 in 40,000 of being a statistical fluke  – making the discrepancy all the more intriguing.

While much of the SM prediction, including contributions from virtual photons and leptons, can be calculated from first principles alone, the strong force contributions involving quarks and gluons are more difficult. However, there is a mathematical link between the strong force contributions to muon g-2 and the probability of experimentally producing hadrons (composite particles made of quarks) from electron–positron annihilation. These so-called “hadronic processes” are something we can observe with existing particle colliders; much like weighing cupcake ingredients, these measurements determine how much each hadronic process contributes to the SM correction to the muon g-2. This is the approach used to calculate the 2020 result, producing what is called a “data-driven” prediction.

Measurements were performed at many experiments, including the BaBar Experiment at the Stanford Linear Accelerator Center (SLAC) in the US, the BESIII Experiment at the Beijing Electron–Positron Collider II in China, the KLOE Experiment at DAFNE Collider in Italy, and the SND and CMD-2 experiments at the VEPP-2000 electron–positron collider in Russia. These different experiments measured a complete catalogue of hadronic processes in different ways over several decades. Myself and other members of the Muon g-2 Theory Initiative combined these findings to produce the data-driven SM prediction of the muon g-2. There was (and still is) strong, corroborating evidence that this SM prediction is reliable.

This discrepancy strongly indicates, to a very high level of confidence, the existence of new physics. It seemed more likely than ever that BSM physics had finally been detected in a laboratory.

That was until the release of the first SM prediction of the muon g-2 using an alternative method called lattice QCD (Nature 593 51). Like the data-driven prediction, lattice QCD is a way to tackle the tricky hadronic contributions, but it doesn’t use experimental results as a basis for the calculation. Instead, it treats the universe as a finite box containing a grid of points (a lattice) that represent points in space and time. Virtual quarks and gluons are simulated inside this box, and the results are extrapolated to a universe of infinite size and continuous space and time. This method requires a huge amount of computer power to arrive at an accurate, physical result but it is a powerful tool that directly simulates the strong-force contributions to the muon g-2.

The researchers who published this new result are also part of the Muon g-2 Theory Initiative. Several other groups within the consortium have since published QCD calculations, producing values for g-2 that are in good agreement with each other and the experiment at Fermilab. “Striking agreement, to better than 1%, is seen between results from multiple groups,” says Christine Davis of the University of Glasgow in the UK, a member of the High-precision lattice QCD (HPQCD) collaboration within the Muon g-2 Theory Initiative. “A range of methods have been developed to improve control of uncertainties meaning further, more complete, lattice QCD calculations are now appearing. The aim is for several results with 0.5% uncertainty in the near future.”

If these lattice QCD predictions are the true SM value, there is no muon g-2 discrepancy between experiment and theory. However, this would conflict with the decades of experimental measurements of hadronic processes that were used to produce the data-driven SM prediction.

To make the situation even more confusing, a new experimental measurement of the muon g-2’s dominant hadronic process was released in 2023 by the CMD-3 experiment (Phys. Rev. D 109 112002). This result is significantly larger than all the other, older measurements of the same process, including its own predecessor experiment, CMD-2 (Phys. Lett. B 648 28). With this new value, the data-driven SM prediction of a_µ = (g – 2)/2 is in agreement with the Muon g-2 experiment and lattice QCD. Over the last few years, the CMD-3 measurements (and all older measurements) have been scrutinized in great detail, but the source of the difference between the measurements remains unknown.

Since then, the Muon g-2 experiment at Fermilab has confirmed and improved on that first result to a precision of 200 ppb (Phys. Rev. Lett. 131 161802). “Our second result based on the data from 2019 and 2020 has been the first step in increasing the precision of the magnetic anomaly measurement,” says Peter Winter of Argonne National Laboratory in the US and co-spokesperson for the Muon g-2 experiment.

The new result is in full agreement with the SM predictions from lattice QCD and the data-driven prediction based on CMD-3’s measurement. However, with the increased precision, it now disagrees with the 2020 SM prediction by even more than in 2021.

The community therefore faces a conundrum. The muon g-2 either exhibits a much-needed discovery of BSM physics or a remarkable, multi-method confirmation of the Standard Model.

On your marks, get set, bake!

In 2025 the Muon g-2 experiment at Fermilab will release its final result. “It will be exciting to see our final result for g-2 in 2025 that will lead to the ultimate precision of 140 parts-per-billion,” says Winter. “This measurement of g-2 will be a benchmark result for years to come for any extension to the Standard Model of particle physics.” Assuming this agrees with the previous results, it will further widen the discrepancy with the 2020 data-driven SM prediction.

For the lattice QCD SM prediction, the many groups calculating the muon’s anomalous magnetic moment have since corroborated and improved the precision of the first lattice QCD result. Their next task is to combine the results from the various lattice QCD predictions to arrive at one SM prediction from lattice QCD. While this is not a trivial task, the agreement between the groups means a single lattice QCD result with improved precision is likely within the next year, increasing the tension with the 2020 data-driven SM prediction.

New, robust experimental measurements of the muon g-2’s dominant hadronic processes are also expected over the next couple of years. The previous experiments will update their measurements with more precise results and a newcomer measurement is expected from the Belle-II experiment in Japan. It is hoped that they will confirm either the catalogue of older hadronic measurements or the newer CMD-3 result. Should they confirm the older data, the potential for new physics in the muon g-2 lives on, but the discrepancy with the lattice QCD predictions will still need to be investigated. If the CMD-3 measurement is confirmed, it is likely the older data will be superseded, and the muon g-2 will have once again confirmed the Standard Model as the best and most resilient description of the fundamental nature of our universe.

The task before the Muon g-2 Theory Initiative is to solve these dilemmas and update the 2020 data-driven SM prediction. Two new publications are planned. The first will be released in 2025 (to coincide with the new experimental result from Fermilab). This will describe the current status and ongoing body of work, but a full, updated SM prediction will have to wait for the second paper, likely to be published several years later.

It’s going to be an exciting few years. Being part of both the experiment and the theory means I have been privileged to see the process from both sides. For the SM prediction, much work is still to be done but science with this much at stake cannot be rushed and it will be fascinating work. I’m looking forward to the journey just as much as the outcome.

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Using an observatory located deep beneath the Mediterranean Sea, an international team has detected an ultra-high-energy cosmic neutrino with an energy greater than 100 PeV, which is well above the previous record. Made by the KM3NeT neutrino observatory, such detections could enhance our understanding of cosmic neutrino sources or reveal new physics.

“We expect neutrinos to originate from very powerful cosmic accelerators that also accelerate other particles, but which have never been clearly identified in the sky. Neutrinos may provide the opportunity to identify these sources,” explains Paul de Jong, a professor at the University of Amsterdam and spokesperson for the KM3NeT collaboration. “Apart from that, the properties of neutrinos themselves have not been studied as well as those of other particles, and further studies of neutrinos could open up possibilities to detect new physics beyond the Standard Model.”

Neutrinos are subatomic particles with masses less than a millionth of that of electrons. They are electrically neutral and interact rarely with matter via the weak force. As a result, neutrinos can travel vast cosmic distances without being deflected by magnetic fields or being absorbed by interstellar material. “[This] makes them very good probes for the study of energetic processes far away in our universe,” de Jong explains.

Scientists expect high-energy neutrinos to come from powerful astrophysical accelerators – objects that are also expected to produce high-energy cosmic rays and gamma rays. These objects include active galactic nuclei powered by supermassive black holes, gamma-ray bursts, and other extreme cosmic events. However, pinpointing such accelerators remains challenging because their cosmic rays are deflected by magnetic fields as they travel to Earth, while their gamma rays can be absorbed on their journey. Neutrinos, however, move in straight lines and this makes them unique messengers that could point back to astrophysical accelerators.

Underwater detection

Because they rarely interact, neutrinos are studied using large-volume detectors. The largest observatories use natural environments such as deep water or ice, which are shielded from most background noise including cosmic rays.

The KM3NeT observatory is situated on the Mediterranean seabed, with detectors more than 2000 m below the surface. Occasionally, a high-energy neutrino will collide with a water molecule, producing a secondary charged particle. This particle moves faster than the speed of light in water, creating a faint flash of Cherenkov radiation. The detector’s array of optical sensors capture these flashes, allowing researchers to reconstruct the neutrino’s direction and energy.

KM3NeT has already identified many high-energy neutrinos, but in 2023 it detected a neutrino with an energy far in excess of any previously detected cosmic neutrino. Now, analysis by de Jong and colleagues puts this neutrino’s energy at about 30 times higher than that of the previous record-holder, which was spotted by the IceCube observatory at the South Pole. “It is a surprising and unexpected event,” he says.

Scientists suspect that such a neutrino could originate from the most powerful cosmic accelerators, such as blazars. The neutrino could also be cosmogenic, being produced when ultra-high-energy cosmic rays interact with the cosmic microwave background radiation.

New class of astrophysical messengers

While this single neutrino has not been traced back to a specific source, it opens the possibility of studying ultra-high-energy neutrinos as a new class of astrophysical messengers. “Regardless of what the source is, our event is spectacular: it tells us that either there are cosmic accelerators that result in these extreme energies, or this could be the first cosmogenic neutrino detected,” de Jong noted.

Neutrino experts not associated with KM3NeT agree on the significance of the observation. Elisa Resconi at the Technical University of Munich tells Physics World, “This discovery confirms that cosmic neutrinos extend to unprecedented energies, suggesting that somewhere in the universe, extreme astrophysical processes – or even exotic phenomena like decaying dark matter – could be producing them”.

Francis Halzen at the University of Wisconsin-Madison, who is IceCube’s principal investigator, adds, “Observing neutrinos with a million times the energy of those produced at Fermilab (ten million for the KM3NeT event!) is a great opportunity to reveal the physics beyond the Standard Model associated with neutrino mass.”

With ongoing upgrades to KM3NeT and other neutrino observatories, scientists hope to detect more of these rare but highly informative particles, bringing them closer to answering fundamental questions in astrophysics.

Resconi, explains, “With a global network of neutrino telescopes, we will detect more of these ultrahigh-energy neutrinos, map the sky in neutrinos, and identify their sources. Once we do, we will be able to use these cosmic messengers to probe fundamental physics in energy regimes far beyond what is possible on Earth.”

The observation is described in Nature.

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Researchers led by Denis Bartolo, a physicist at the École Normale Supérieure (ENS) of Lyon, France, have constructed a theoretical model that forecasts the movements of confined, densely packed crowds. The study could help predict potentially life-threatening crowd behaviour in confined environments. 

To investigate what makes some confined crowds safe and others dangerous, Bartolo and colleagues – also from the Université Claude Bernard Lyon 1 in France and the Universidad de Navarra in Pamplona, Spain – studied the Chupinazo opening ceremony of the San Fermín Festival in Pamplona in four different years (2019, 2022, 2023 and 2024).

The team analysed high-resolution video captured from two locations above the gathering of around 5000 people as the crowd grew in the 50 x 20 m city plaza: swelling from two to six people per square metre, and ultimately peaking at local densities of nine per square metre. A machine-learning algorithm enabled automated detection of the position of each person’s head; from which localized crowd density was then calculated.

“The Chupinazo is an ideal experimental platform to study the spontaneous motion of crowds, as it repeats from one year to the next with approximately the same amount of people, and the geometry of the plaza remains the same,” says theoretical physicist Benjamin Guiselin, a study co-author formerly from ENS Lyon and now at the Université de Montpellier.

In a first for crowd studies, the researchers treated the densely packed crowd as a continuum like water, and “constructed a mechanics theory for the crowd movement without making any behavioural assumptions on the motion of individuals,” Guiselin tells Physics World.

Their studies, recently described in Nature, revealed a change in behaviour akin to a phase change when the crowd density passed a critical threshold of four individuals per square metre. Below this density the crowd remained relatively inactive. But above that threshold it started moving, exhibiting localized oscillations that were periodic over about 18 s, and occurred without any external guiding such as corralling.

Unlike a back-and-forth oscillation, this motion – which involves hundreds of people moving over several metres – has an almost circular trajectory that shows chirality (or handedness) and a 50:50 chance of turning to either the right or left. “Our model captures the fact that the chirality is not fixed. Instead it emerges in the dynamics: the crowd spontaneously decides between clockwise or counter-clockwise circular motion,” explains Guiselin, who worked on the mathematical modelling.

“The dynamics is complicated because if the crowd is pushed, then it will react by creating a propulsion force in the direction in which it is pushed: we’ve called this the windsock effect. But the crowd also has a resistance mechanism, a counter-reactive effect, which is a propulsive force opposite to the direction of motion: what we have called the weathercock effect,” continues Guiselin, adding that it is these two competing mechanisms in conjunction with the confined situation that gives rise to the circular oscillations.

The team observed similar oscillations in footage of the 2010 tragedy at the Love Parade music festival in Duisburg, Germany, in which 21 people died and several hundred were injured during a crush.

Early results suggest that the oscillation period for such crowds is proportional to the size of the space they are confined in. But the team want to test their theory at other events, and learn more about both the circular oscillations and the compression waves they observed when people started pushing their way into the already crowded square at the Chupinazo.

If their model is proven to work for all densely packed, confined crowds, it could in principle form the basis for a crowd management protocol. “You could monitor crowd motion with a camera, and as soon as you detect these oscillations emerging try to evacuate the space, because we see these oscillations well before larger amplitude motions set in,” Guiselin explains.

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Scientists across the US have been left reeling after a spate of executive orders from US President Donald Trump has led to research funding being slashed, staff being told to quit and key programmes being withdrawn. In response to the orders, government departments and external organizations have axed diversity, equity and inclusion (DEI) programmes, scrubbed mentions of climate change from websites, and paused research grants pending tests for compliance with the new administration’s goals.

Since taking up office on 20 January, Trump has signed dozens of executive orders. One ordered the closure of the US Agency for International Development, which has supported medical and other missions worldwide for more than six decades. The administration said it was withdrawing almost all of the agency’s funds and wanted to sack its entire workforce. A federal judge has temporarily blocked the plans, saying they may violate the US’s constitution, which reserves decisions on funding to Congress.

Individual science agencies are under threat too. Politico reported that the Trump administration has asked the National Science Foundation (NSF), which funds much US basic and applied research, to lay off between a quarter and a half of its staff in the next two months. Another report suggests there are plans to cut the agency’s annual budget from roughly $9bn to $3bn. Meanwhile, former officials of the National Oceanic and Atmospheric Administration (NOAA) told CBS News that half its staff could be sacked and its budget slashed by 30%.

Even before they had learnt of plans to cut its staff and budget, officials at the NSF were starting to examine details of thousands of grants it had awarded for references to DEI, climate change and other topics that Trump does not like. The swiftness of the announcements has caused chaos, with recipients of grants suddenly finding themselves unable to access the NSF’s award cash management service, which holds grantees’ funds, including their salaries.

NSF bosses have taken some steps to reassure grantees. “Our top priority is resuming our funding actions and services to the research community and our stakeholders,” NSF spokesperson Mike England told Physics World in late January. In what is a highly fluid situation, there was some respite on 2 February when the NSF announced that access had been restored with the system able to accept payment requests.

“Un-American” actions

Trump’s anti-DEI orders have caused shockwaves throughout US science. According to 404 Media, NASA staff were told on 22 January to “drop everything” to remove mentions of DEI, Indigenous people, environmental justice and women in leadership, from public websites. Another victim has been NASA’s Here to Observe programme, which links undergraduates from under-represented groups with scientists who oversee NASA’s missions. Science reported that contracts for half the scientists involved in the programme had been cancelled by the end of January.

It is still unclear, however, what impact the Trump administration’s DEI rules will have on the make-up of NASA’s astronaut corps. Since choosing its first female astronaut in 1978, NASA has sought to make the corps more representative of US demographics. How exactly the agency should move forward will fall to Jared Isaacman, the space entrepreneur and commercial astronaut who has been nominated as NASA’s next administrator.

Anti-DEI initiatives have hit individual research labs too. Physics World understands that Fermilab – the US’s premier particle-physics lab – suspended its DEI office and its women in engineering group in January. Meanwhile, the Fermilab LBGTQ+ group, called Spectrum, was ordered to cease all activities and its mailing list deleted. Even the rainbow “Pride” flag was removed from the lab’s iconic Wilson Hall.

Some US learned societies, despite being formally unaffiliated with the government, have also responded to pressure from the new administration. The American Geophysical Union (AGU) removed the word “diversity” from its diversity and inclusion page, although it backtracked after criticism of the move.

There was also some confusion that the American Chemical Society had removed its webpage on diversity and inclusion, but they had in fact published a new page and failed to put a redirect in place. “Inclusion and Belonging is a core value of the American Chemical Society, and we remain committed to creating environments where people from diverse backgrounds, cultures, perspectives and experiences thrive,” a spokesperson told Physics World. “We know the broken link caused confusion and some alarm, and we apologize.”

For the time being, the American Physical Society’s page on inclusion remains live, as does that of the American Institute of Physics.

Dismantling all federal DEI programmes and related activities will damage lives and careers of millions of American women and men

Neal Lane, Rice University

Such a response – which some opponents denounce as going beyond what is legally required for fear of repercussions if no action is taken – has left it up to individual leaders to underline the importance of diversity in science. Neal Lane, a former science adviser to President Clinton, told Physics World that “dismantling all federal DEI programmes and related activities will damage lives and careers of millions of American women and men, including scientists, engineers, technical workers – essentially everyone who contributes to advancing America’s global leadership in science and technology”.

Lane, who is now a science and technology policy fellow at Rice University in Texas, think that the new administration’s anti-DEI actions “will weaken the US” and believes they should be considered “un-American”. “The purpose of DEI policies programmes and activities is to ensure all Americans have the opportunity to participate and the country is able to benefit from their participation,” he says.

One senior physicist at a US university, who wishes to remain anonymous, told Physics World that those behind the executive orders are relying on institutions and individuals to “comply in advance” with what they perceive to be the spirit of the orders. “They are relying on people to ignore the fine print, which says that executive orders can’t and don’t overwrite existing law. But it is up to scientists to do the reading — and to follow our consciences. More than universities are on the line: the lives of our students and colleagues are on the line.”

Education turmoil

Another target of the Trump administration is the US Department of Education, which was set up in 1978 to oversee everything from pre-school to postgraduate education. It has already put dozens of its civil servants on leave, ostensibly because their work involves DEI issues. Meanwhile, the withholding of funds has led to the cancellation of scientific meetings, mostly focusing on medicine and life sciences, that were scheduled in the US for late January and early February.

Colleges and universities in the US have also reacted to Trump’s anti-DEI executive order. Academic divisions at Harvard University and the Massachusetts Institute of Technology, for example, have already indicated that they will no longer require applicants for jobs to indicate how they plan to advance the goals of DEI. Northeastern University in Boston has removed the words “diversity” and “inclusion” from a section of its website.

Not all academic organizations have fallen into line, however. Danielle Holly, president of the women-only Mount Holyoke College in South Hadley, Massachusetts, says it will forgo contracts with the federal government if they required abolishing DEI. “We obviously can’t enter into contracts with people who don’t allow DEI work,” she told the Boston Globe. “So for us, that wouldn’t be an option.”

Climate concerns

For an administration that doubts the reality of climate change and opposes anti-pollution laws, the Environmental Protection Agency (EPA) is under fire too. Trump administration representatives were taking action even before the Senate approved Lee Zeldin, a former Republican Congressman from New York who has criticized much environmental legislation, as EPA Administrator. They removed all outside advisers on the EPA’s scientific advisory board and its clean air scientific advisory committee – purportedly to “depoliticize” the boards.

Once the Senate approved Zeldin on 29 January, the EPA sent an e-mail warning more than 1000 probationary employees who had spent less than a year in the agency that their roles could be “terminated” immediately. Then, according to the New York Times, the agency developed plans to demote longer-term employees who have overseen research, enforcement of anti-pollution laws, and clean-ups of hazardous waste. According to Inside Climate News, staff also found their individual pronouns scrubbed from their e-mails and websites without their permission – the result of an order to remove “gender ideology extremism”.

Critics have also questioned the nomination of Neil Jacobs to lead the NOAA. He was its acting head during Trump’s first term in office, serving during the 2019 “Sharpiegate” affair when Trump used a Sharpie pen to alter a NOAA weather map to indicate that Hurricane Dorian would affect Alabama. While conceding Jacobs’s experience and credentials, Rachel Cleetus of the Union of Concerned Scientists asserts that Jacobs is “unfit to lead” given that he “fail[ed] to uphold scientific integrity at the agency”.

Spending cuts

Another concern for scientists is the quasi-official team led by “special government employee” and SpaceX founder Elon Musk. The administration has charged Musk and his so-called “department of government efficiency”, or DOGE, to identify significant cuts to government spending. Though some of DOGE’s activities have been blocked by US courts, agencies have nevertheless been left scrambling for ways to reduce day-to-day costs.

The National Institutes of Health (NIH), for example, has said it will significantly reduce its funding for “indirect” costs of research projects it supported – the overheads that, for example, cover the cost of maintaining laboratories, administering grants, and paying staff salaries. Under the plans, indirect cost reimbursement for federally funded research would be capped at 15%, a drastic cut from its usual range.

NIH personnel have tried to put a positive gloss on its actions. “The United States should have the best medical research in the world,” a statement from NIH declared. “It is accordingly vital to ensure that as many funds as possible go towards direct scientific research costs rather than administrative overhead.”

Just because Elon Musk doesn’t understand indirect costs doesn’t mean Americans should have to pay the price with their lives

US senator Patty Murray

Opponents of the Trump administration, however, are unconvinced. They argue that the measure will imperil critical clinical research because many academic recipients of NIH funds did not have the endowments to compensate for the losses. “Just because Elon Musk doesn’t understand indirect costs doesn’t mean Americans should have to pay the price with their lives,” says US senator Patty Murray, a Democrat from Washington state.

Slashing universities’ share of grants to below 15%, could, however, force institutions to make up the lost income by raising tuition fees, which could “go through the roof”, according to the anonymous senior physicist contacted by Physics World. “Far from being a populist policy, these cuts to overheads are an attack on the subsidies that make university education possible for students from a range of socioeconomic backgrounds. The alternative is to essentially shut down the university research apparatus, which would in many ways be the death of American scientific leadership and innovation.”

Musk and colleagues have also gained unprecedented access to government websites related to civil servants and the country’s entire payments system. That access has drawn criticism from several commentators who note that, since Musk is a recipient of significant government support through his SpaceX company, he could use the information for his own advantage.

“Musk has access to all the data on federal research grantees and contractors: social security numbers, tax returns, tax payments, tax rebates, grant disbursements and more,” wrote physicist Michael Lubell from City College of New York. “Anyone who depends on the federal government and doesn’t toe the line might become a target. This is right out of (Hungarian prime minister) Viktor Orbán’s playbook.”

A new ‘dark ages’

As for the long-term impact of these changes, James Gates – a theoretical physicist at the University of Maryland and a past president of the US National Society of Black Physicists – is blunt. “My country is in for a 50-year period of a new dark ages,” he told an audience at the Royal College of Art in London, UK, on 7 February.

My country is in for a 50-year period of a new dark ages

James Gates, University of Maryland

Speaking at an event sponsored by the college’s association for Black students – RCA BLK – and supported by the UK’s organization for Black physicists, the Blackett Lab Family, he pointed out that the US has been through such periods before. As examples, Gates cited the 1950s “Red Scare” and the period after 1876 when the federal government abandoned efforts to enforce the civil rights of Black Americans in southern states and elsewhere.

However, he is not entirely pessimistic. “Nothing is permanent in human behaviour. The question is the timescale,” Gates said. “There will be another dawn, because that’s part of the human spirit.”

• With additional reporting by Margaret Harris, online editor of Physics World, in London and Michael Banks, news editor of Physics World

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IBM is on a mission to transform quantum computers from applied research endeavour to mainstream commercial opportunity. It wants to go beyond initial demonstrations of “quantum utility”, where these devices outperform classical computers only in a few niche applications, and reach the new frontier of “quantum advantage”. That’ll be where quantum computers routinely deliver significant, practical benefits beyond approximate classical computing methods, calculating solutions that are cheaper, faster and more accurate.

Unlike classical computers, which rely on the binary bits that can be either 0 or 1, quantum computers exploit quantum binary bits (qubits), but as a superposition of 0 and 1 states. This superposition, coupled with quantum entanglement (a correlation of two qubits), enables quantum computers to perform some types of calculation significantly faster than classical machines, such as problems in quantum chemistry and molecular reaction kinetics.

In the vanguard of IBM’s quantum R&D effort is Sarah Sheldon, a principal research scientist and senior manager of quantum theory and capabilities at the IBM Thomas J Watson Research Center in Yorktown Heights, New York. After a double-major undergraduate degree in physics and nuclear science and engineering at Massachusetts Institute of Technology (MIT), Sheldon received her PhD from MIT in 2013 – though she did much of her graduate research in nuclear science and engineering as a visiting scholar at the Institute for Quantum Computing (IQC) at the University of Waterloo, Canada.

At IQC, Sheldon was part of a group studying quantum control techniques, manipulating the spin states of nuclei in nuclear-magnetic-resonance (NMR) experiments. “Although we were using different systems to today’s leading quantum platforms, we were applying a lot of the same kinds of control techniques now widely deployed across the quantum tech sector,” Sheldon explains.

“Upon completion of my PhD, I opted instinctively for a move into industry, seeking to apply all that learning in quantum physics into immediate and practical engineering contributions,” she says. “IBM, as one of only a few industry players back then with an experimental group in quantum computing, was the logical next step.”

Physics insights, engineering solutions

Sheldon currently heads a cross-disciplinary team of scientists and engineers developing techniques for handling noise and optimizing performance in novel experimental demonstrations of quantum computers. It’s ambitious work that ties together diverse lines of enquiry spanning everything from quantum theory and algorithm development to error mitigation, error correction and techniques for characterizing quantum devices.

We’re investigating how to extract the optimum performance from current machines online today as well as from future generations of quantum computers.

Sarah Sheldon, IBM

“From algorithms to applications,” says Sheldon, “we’re investigating what can we do with quantum computers: how to extract the optimum performance from current machines online today as well as from future generations of quantum computers – say, five or 10 years down the line.”

A core priority for Sheldon and colleagues is how to manage the environmental noise that plagues current quantum computing systems. Qubits are all too easily disturbed, for example, by their interactions with environmental fluctuations in temperature, electric and magnetic fields, vibrations, stray radiation and even interference between neighbouring qubits.

The ideal solution – a strategy called error correction – involves storing the same information across multiple qubits, such that errors are detected and corrected when one or more of the qubits are impacted by noise. But the problem with these so-called “fault-tolerant” quantum computers is they need millions of qubits, which is impossible to implement in today’s small-scale quantum architectures. (For context, IBM’s latest Quantum Development Roadmap outlines a practical path to error-corrected quantum computers by 2029.)

“Ultimately,” Sheldon notes, “we’re working towards large-scale error-corrected systems, though for now we’re exploiting near-term techniques like error mitigation and other ways of managing noise in these systems.” In practical terms, this means implementing quantum architectures without increasing the number of qubits – essentially, integrating them with classical computers to reduce noise through increasing samples on the quantum computer combined with classical processing.

Strength in diversity

For Sheldon, one big selling point of the quantum tech industry is the opportunity to collaborate with people from a wide range of disciplines. “My team covers a broad-scope R&D canvas,” she says. There are mathematicians and computer scientists, for example, working on complexity theory and novel algorithm development; physicists specializing in quantum simulation and incorporating error suppression techniques; as well as quantum chemists working on simulations of molecular systems.

“Quantum is so interdisciplinary – you are constantly learning something new from your co-workers,” she adds. “I started out specializing in quantum control techniques, before moving onto experimental demonstrations of larger multiqubit systems while working ever more closely with theorists.”

External research collaborations are also mandatory for Sheldon and her colleagues. Front-and-centre is the IBM Quantum Network, which provides engagement opportunities with more than 250 organizations across the “quantum ecosystem”. These range from top-tier labs – such as CERN, the University of Tokyo and the UK’s National Quantum Computing Centre – to quantum technology start-ups like Q-CTRL and Algorithmiq. It also encompasses established industry players aiming to be early-adopting end-users of quantum technologies (among them Bosch, Boeing and HSBC).

“There’s a lot of innovation happening across the quantum community,” says Sheldon, “so external partnerships are incredibly important for IBM’s quantum R&D programme. While we have a deep and diverse skill set in-house, we can’t be the domain experts across every potential use-case for quantum computing.”

Opportunity knocks

Notwithstanding the pace of innovation, there are troubling clouds on the horizon. In particular, there is a shortage of skilled workers in the quantum workforce, with established technology companies and start-ups alike desperate to attract more physical scientists and engineers. The task is to fill not only specialist roles – be it error-correction scientists or quantum-algorithm developers – but more general positions such as test and measurement engineers, data scientists, cryogenic technicians and circuit designers.

Yet Sheldon remains upbeat about addressing the skills gap. “There are just so many opportunities in the quantum sector,” she notes. “The field has changed beyond all recognition since I finished my PhD.” Perhaps the biggest shift has been the dramatic growth of industry engagement and, with it, all sorts of attractive career pathways for graduate scientists and engineers. Those range from firms developing quantum software or hardware to the end-users of quantum technologies in sectors such as pharmaceuticals, finance or healthcare.

“As for the scientific community,” argues Sheldon, “we’re also seeing the outline take shape for a new class of quantum computational scientist. Make no mistake, students able to integrate quantum computing capabilities into their research projects will be at the leading edge of their fields in the coming decades.”

Ultimately, Sheldon concludes, early-career scientists shouldn’t necessarily over-think things regarding that near-term professional pathway. “Keep it simple and work with people you like on projects that are going to interest you – whether quantum or otherwise.”

The post Sarah Sheldon: how a multidisciplinary mindset can turn quantum utility into quantum advantage appeared first on Physics World.

International conferences are a great way to meet people from all over the world to share the excitement of physics and discuss the latest developments in the subject. But the International Conference on Women in Physics (ICWIP) offers more by allowing us to to listen to the experiences of people from many diverse backgrounds and cultures. At the same time, it highlights the many challenges that women in physics still face.

The ICWIP series is organized by the International Union of Pure and Applied Physics (IUPAP) and the week-long event typically features a mixture of plenaries, workshops and talks. Prior to the COVID-19 pandemic, the conferences were held in various locations across the world, but the last two have been held entirely online. The last such meeting – the 8th ICWIP run from India in 2023 – saw around 300 colleagues from 57 countries attend. I was part of a seven-strong UK contingent – at various stages of our careers – who gave a presentation describing the current situation for women in physics in the UK.

Being held solely online didn’t stop delegates fostering a sense of community or discussing their predicaments and challenges. What became evident during the week was the extent and types of issues that women from across the globe still have to contend with. One is the persistence of implicit and explicit gender bias in their institutions or workplaces. This, along with negative stereotyping of women, produces discrepancies between male and female numbers in institutions, particularly at postgraduate level and beyond. Women often end up choosing not to pursue physics later into their careers and being reluctant to take up leadership roles.

Much more needs to be done to ensure women are encouraged in their careers. Indeed, women often face challenging work–life balances, with some expected to play a greater role in family commitments than men, and have little support at their workplaces. One postdoctoral researcher at the 2023 meeting, for example, attempted to discuss her research poster in the virtual conference room while looking after her young children at home – the literal balancing of work and life in action.

To improve their circumstances, delegates suggested enhancing legislation to combat gender bias and improve institutional culture through education to reduce negative stereotypes. More should also be done to improve networks and professional associations for women in physics. Another factor mentioned at the meeting, meanwhile, is the importance of early education and issues related to equity of teaching, whether delivered face-to-face or online.

But women can face disadvantages other than their gender, such as socioeconomic status and identity, resulting in a unique set of challenges for them. This is the principle of intersectionality and was widely discussed in the context of problems in career progression.

In the UK, change is starting to happen. The Limit Less campaign by the Institute of Physics (IOP), which publishes Physics World, encourages students post 16 years old to study physics. The annual Conference for Undergraduate Women and Non-binary Physicists provides individuals with support and encouragement in their personal and professional development. There are also other initiatives such as the STEM Returner programme and the Daphne Jackson Trust for those wishing to return to a physics career. WISE Ten Steps contributes to supporting workplace culture positively and the Athena SWAN and the IOP’s new Physics Inclusion Award aims to improve women’s prospects.

As we now look forward to the next ICWIP there is still a lot more to do. We must ensure that women can continue in their physics careers while recognizing that intersectionality will play an increasingly significant role in shaping future equity, diversity and inclusion policies. It is likely that soon a new team will be sought from academia and industry, comprising of individuals at various career stages to represent the UK at the next ICWIP. Please do get involved if you are interested. Participation is not limited to women.

Women are doing physics in a variety of challenging circumstances. Gaining an international outlook of different cultural perspectives, as is possible at an international conference like the ICWIP, helps to put things in context and highlights the many common issues faced by women in physics. Taking the time to listen and learn from each other is critical, a process that can facilitate collaboration on issues that affect us all. Fundamentally, we all share a passion for physics, and endeavour to be catalysts for positive change for future generations.

• This article was based on discussions with Sally Jordan from the Open University; Holly Campbell, UK Atomic Energy Authority; Josie C, AWE; Wendy Sadler and Nils Rehm, Cardiff University; and Sarah Bakewell and Miriam Dembo, Institute of Physics

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A new type of quantum bit (qubit) that stores information in a quantum dot with the help of an ensemble of nuclear spin states has been unveiled by physicists in the UK and Austria. Led by Dorian Gangloff and Mete Atatüre at the University of Cambridge, the team created a collective quantum state that could be used as a quantum register to store and relay information in a quantum communication network of the future.

Quantum communication networks are used to exchange and distribute quantum information between remotely-located quantum computers and other devices. As well as enabling distributed quantum computing, quantum networks can also support secure quantum cryptography. Today, these networks are in the very early stages of development and use the entangled quantum states of photons to transmit information. Network performance is severely limited by decoherence, whereby the quantum information held by photons is degraded as they travel long distances. As a result, effective networks need repeater nodes that receive and then amplify weakened quantum signals.

“To address these limitations, researchers have focused on developing quantum memories capable of reliably storing entangled states to enable quantum repeater operations over extended distances,” Gangloff explains. “Various quantum systems are being explored, with semiconductor quantum dots being the best single-photon generators delivering both photon coherence and brightness.”

Single-photon emission

Quantum dots are widely used for their ability to emit single photons at specific wavelengths. These photons are created by electronic transitions in quantum dots and are ideal for encoding and transmitting quantum information.

However, the electronic spin states of quantum dots are not particularly good at storing quantum information for long enough to be useful as stationary qubits (or nodes) in a quantum network. This is because they contain hundreds or thousands of nuclei with spins that fluctuate. The noise generated by these fluctuations causes the decoherence of qubits based on electronic spin states.

In their previous research, Gangloff and Atatüre’s team showed how this noise could be controlled by sensing how it interacts with the electronic spin states.

Atatüre says, “Building on our previous achievements, we suppressed random fluctuations in the nuclear ensemble using a quantum feedback algorithm. This is already very useful as it dramatically improves the electron spin qubit performance.”

Magnon excitation

Now, using a gallium arsenide quantum dot, the team has used the feedback algorithm to stabilize 13,000 nuclear spin states in a collective, entangled “dark state”. This is a stable quantum state that cannot absorb or emit photons. By introducing just a single nuclear magnon (spin flip) excitation, shared across all 13,000 nuclei, they could then flip the entire ensemble between two different collective quantum states.

Each of these collective states could respectively be defined as a 0 and a 1 in a binary quantum logic system. The team then showed how quantum information could be exchanged between the nuclear system and the quantum dot’s electronic qubit with a fidelity of about 70%.

“The quantum memory maintained the stored state for approximately 130 µs, validating the effectiveness of our protocol,” Gangloff explains. “We also identified unambiguously the factors limiting the current fidelity and storage time, including crosstalk between nuclear modes and optically induced spin relaxation.”

The researchers are hopeful that their approach could transform one of the biggest limitations to quantum dot-based communication networks into a significant advantage.

“By integrating a multi-qubit register with quantum dots – the brightest and already commercially available single-photon sources – we elevate these devices to a much higher technology readiness level,” Atatüre explains.

With some further improvements to their system’s fidelity, the researchers are now confident that it could be used to strengthen interactions between quantum dot qubits and the photonic states they produce, ultimately leading to longer coherence times in quantum communication networks. Elsewhere, it could even be used to explore new quantum phenomena, and gather new insights into the intricate dynamics of quantum many-body systems.

The research is described in Nature Physics.

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Unexpected behaviour at phase transitions between classical and quantum magnetism has been observed in different quantum simulators operated by two independent groups. One investigation was led by researchers at Harvard University and used Rydberg atom as quantum bits (qubits). The other study was led by scientists at  Google Research and involved superconducting qubits. Both projects revealed unexpected deviations from the canonical mechanisms of magnetic freezing, with unexpected oscillations near the phase transition.

A classical magnetic material can be understood as a fluid mixture of magnetic domains that are oriented in opposite directions, with the domain walls in constant motion. As a strengthening magnetic field is applied to the system, the energy associated with a domain wall increases, so the magnetic domains themselves become larger and less mobile. At some point, when the magnetism becomes sufficiently strong, a quantum phase transition occurs, causing the magnetism of the material to become fixed and crystalline: “A good analogy is like water freezing,” says Mikhail Lukin of Harvard University.

The traditional quantitative model for these transitions is the Kibble–Zurek mechanism, which was first formulated to describe cosmological phase transitions in the early universe. It predicts that the dynamics of a system begin to “freeze” when the system gets so close to the transition point that the domains crystallize more quickly than they can come to equilibrium.

“There are some very good theories of various types of quantum phase transitions that have been developed,” says Lukin, “but typically these theories make some approximations. In many cases they’re fantastic approximations that allow you to get very good results, but they make some assumptions which may or may not be correct.”

Highly reconfigurable platform

In their work, Lukin and colleagues utilized a highly reconfigurable platform using Rydberg atom qubits. The system was pioneered by Lukin and others in 2016 to study a specific type of magnetic quantum phase transition in detail. They used a laser to simulate the effect of a magnetic field on the Rydberg atoms, and adjusted the laser frequency to tune the field strength.

The researchers found that, rather than simply becoming progressively larger and less mobile as the field strength increased (a phenomenon called coarsening), the domain sizes underwent unexpected oscillations around the phase transition.

“We were really quite puzzled,” says Lukin. “Eventually we figured out that this oscillation is a sign of a special type of excitation mode similar to the Higgs mode in high-energy physics. This is something we did not anticipate…That’s an example where doing quantum simulations on quantum devices really can lead to new discoveries.”

Meanwhile, the Google-led study used a new approach to quantum simulation with superconducting qubits. Such qubits have proved extremely successful and scalable because they use solid-state technology – and they are used in most of the world’s leading commercial quantum computers such as IBM’s Osprey and Google’s own Willow chips. Much of the previous work using such chips, however, has focused on sequential “digital” quantum logic in which one set of gates is activated only after the previous set has concluded. The long times needed for such calculations allows the effects of noise to accumulate, resulting in computational errors.

Hybrid approach

In the new work, the Google team developed a hybrid analogue–digital approach in which a digital universal quantum gate set was used to prepare well-defined input qubit states. They then switched the processor to analogue mode, using capacitive couplers to tune the interactions between the qubits. In this mode, all the qubits were allowed to operate on each other simultaneously, without the quantum logic being shoehorned into a linear set of gate operations. Finally, the researchers characterized the output by switching back to digital mode.

The researchers used a 69-qubit superconducting system to simulate a similar, but non-identical, magnetic quantum phase transition to that studied by Lukin’s group. They were also puzzled by similar unexpected behaviour in their system. The groups’ subsequently became aware of each other’s work, as Google Research’s Trond Anderson explains: “It’s very exciting to see consistent observations from the Lukin group. This not only provides supporting evidence, but also demonstrates that the phenomenon appears in several contexts, making it extra important to understand”.

Both groups are now seeking to push their research deeper into the exploration of complex many-body quantum physics. The Google group estimates that, to conduct its simulations of the highly entangled quantum states involved with the same level of experimental fidelity would take the US Department of Energy’s Frontier supercomputer – one of the world’s most powerful – more than a million years. The researchers now want to look at problems that are completely intractable classically, such as magnetic frustration. “The analogue–digital approach really combines the best of both worlds, and we’re very excited about this as a new promising direction towards making discoveries in systems that are too complex for classical computers,” says Anderson.

The Harvard researchers are also looking to push their system to study more and more complex quantum systems. “There are many interesting processes where dynamics – especially across a quantum phase transition – remains poorly understood,” says Lukin. “And it ranges from the science of complex quantum materials to systems in high-energy physics such as lattice gauge theories, which are notorious for being hard to simulate classically to the point where people literally give up…We want to apply these kinds of simulators to real open quantum problems and really use them to study the dynamics of these systems.”

The research is described in side-by-side papers in Nature. The Google paper is here and the Harvard paper here.

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An international team of researchers has detected a series of significant X-ray oscillations near the innermost orbit of a supermassive black hole – an unprecedented discovery that could indicate the presence of a nearby stellar-mass orbiter such as a white dwarf.

Optical outburst

The Massachusetts Institute of Technology (MIT)-led team began studying the extreme supermassive black hole 1ES 1927+654 – located around 270 million light years away and about a million times more massive than the Sun – in 2018, when it brightened by a factor of around 100 at optical wavelengths. Shortly after this optical outburst, X-ray monitoring revealed a period of dramatic variability as X-rays dropped rapidly – at first becoming undetectable for about a month, before returning with a vengeance and transforming into the brightest supermassive black hole in the X-ray sky.

“All of this dramatic variability seemed to be over by 2021, as the source appeared to have returned to its pre-2018 state. However, luckily, we continued to watch this source, having learned the lesson that this supermassive black hole will always surprise us. The discovery of these millihertz oscillations was indeed quite a surprise, but it gives us a direct probe of regions very close to the supermassive black hole,” says Megan Masterson, a fifth-year PhD candidate at the MIT Kavli Institute for Astrophysics and Space Research, who co-led the study with MIT’s Erin Kara – alongside researchers based elsewhere in the US, as well as at institutions in Chile, China, Israel, Italy, Spain and the UK.

“We found that the period of these oscillations rapidly changed – dropping from around 18 minutes in 2022 to around seven minutes in 2024. This period evolution is unprecedented, having never been seen before in the small handful of other supermassive black holes that show similar oscillatory behaviour,” she adds.

White dwarf

According to Masterson, one of the key ideas behind the study was that the rapid X-ray period change could be driven by a white dwarf – the compact remnant of a star like our Sun – orbiting around the supermassive black hole close to its event horizon.

“If this white dwarf is driving these oscillations, it should produce a gravitational wave signal that will be detectable with next-generation gravitational wave observatories, like ESA’s Laser Interferometer Space Antenna (LISA),” she says.

To test their hypothesis, the researchers used X-ray data from ESA’s XMM-Newton observatory to detect the oscillations, which allowed them to track how the X-ray brightness changed over time. The findings were presented in mid-January at the 245th meeting of the American Astronomical Society in National Harbor, Maryland, and subsequently reported in Nature.

According to Masterson, these insights into the behaviour of X-rays near a black hole will have major implications for future efforts to detect multi-messenger signals from supermassive black holes.

“We really don’t understand how common stellar-mass companions around supermassive black holes are, but these findings tell us that it may be possible for stellar-mass objects to survive very close to supermassive black holes and produce gravitational wave signals that will be detected with the next-generation gravitational wave observatories,” she says.

Looking ahead, Masterson confirms that the immediate next step for MIT research in this area is to continue to monitor 1ES 1927+654 – with both existing and future telescopes – in an effort to deepen understanding of the extreme physics at play in and around the innermost environments of black holes.

“We’ve learned from this discovery that we should expect the unexpected with this source,” she adds. “We’re also hoping to find other sources like this one through large time-domain surveys and dedicated X-ray follow-up of interesting transients.”

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A sample of asteroid dirt brought back to Earth by NASA’s OSIRIS-REx mission contains amino acids and the nucleobases of RNA and DNA, plus brines that could have facilitated the formation of organic molecules, scanning electron microscopy has shown.

The 120 g of material came from the near-Earth asteroid 101955 Bennu, which OSIRIS-REx visited in 2020. The findings “bolster the hypothesis that asteroids like Bennu could have delivered the raw ingredients to Earth prior to the emergence of life,” Dan Glavin of NASA’s Goddard Space Flight Center tells Physics World.

Bennu has an interesting history. It is 565 m across at its widest point and was once part of a much larger parent body, possibly 100 km in diameter, that was smashed apart in a collision in the Asteroid Belt between 730 million and 1.55 billion years ago. Bennu coalesced from the debris as a rubble pile that found itself in Earth’s vicinity.

The sample from Bennu was parachuted back to Earth in 2023 and shared among teams of researchers. Now two new papers, published in Nature and Nature Astronomy, reveal some of the findings from those teams.

Saltwater residue

In particular, researchers identified a diverse range of salt minerals, including sodium-bearing phosphates and carbonates that formed brines when liquid water on Bennu’s parent body either evaporated or froze.

The liquid water would have been present on Bennu’s parent during the dawn of the Solar System, in the first few million years after the planets began to form. Heat generated by the radioactive decay of aluminium-26 would have kept pockets of water liquid deep inside Bennu’s parent body. The brines that this liquid water bequeathed would have played a role in kickstarting organic chemistry.

Tim McCoy, of the Smithsonian’s National Museum of Natural History and the lead author of the Nature paper, says that “brines play two important roles”.

One of those roles is producing the minerals that serve as templates for organic molecules. “As an example, brines precipitate phosphates that can serve as a template on which sugars needed for life are formed,” McCoy tells Physics World. The phosphate is like a pegboard with holes, and atoms can use those spaces to arrange themselves into sugar molecules.

The second role that brines can play is to then release the organic molecules that have formed on the minerals back into the brine, where they can combine with other organic molecules to form more complex compounds.

Ambidextrous amino acids

Meanwhile, the study reported in Nature Astronomy, led by Dan Glavin and Jason Dworkin of NASA’s Goddard Space Flight Center, focused on the detection of 14 of the 20 amino acids used by life to build proteins, deepening the mystery of why life only uses “left-handed” amino acids.

Amino acid molecules lack rotational symmetry – think of how, no matter how much you twist or turn your left hand, you will never be able to superimpose it on your right hand. As such, amino acids can randomly be either left- or right-handed, a property known as chirality.

However, for some reason that no one has been able to figure out yet, all life on Earth uses left-handed amino acids.

One hypothesis was that due to some quirk, amino acids formed in space and brought to Earth in impacts had a bias for being left-handed. This possibility now looks unlikely after Glavin and Dworkin’s team discovered that the amino acids in the Bennu sample are a mix of left- and right-handed, with no evidence that one is preferred over the other.

“So far we have not seen any evidence for a preferred chirality,” Glavin says. This goes for both the Bennu sample and a previous sample from the asteroid 162173 Ryugu, collected by Japan’s Hayabusa2 mission, which contained 23 different forms of amino acid. “For now, why life turned left on Earth remains a mystery.”

Taking a closer step to the origin of life

Another mystery is why the organic chemistry on Bennu’s parent body reached a certain point and then stopped. Why didn’t it form more complex organic molecules, or even life?

Amino acids are the construction blocks of proteins. In turn, proteins are one of the primary molecules for life, facilitating biological processes within cells. Nucleobases have also been identified in the Bennu sample, but although chains of nucleobases are the molecular skeleton of RNA and DNA, neither nucleic acid has been found in an extraterrestrial sample yet.

“Although the wet and salty conditions inside Bennu’s parent body provided an ideal environment for the formation of amino acids and nucleobases, it is not clear yet why more complex organic polymers did not evolve,” says Glavin.

Researchers are still looking for that complex chemistry. McCoy cites the 5-carbon sugar ribose, which is a component of RNA, as an essential organic molecule for life that scientists hope to one day find in an asteroid sample.

“But as you might imagine, as organic molecules increase in complexity, they decrease in number,” says McCoy, explaining that we will need to search ever larger amounts of asteroidal material before we might get lucky and find them.

The answers will ultimately help astrobiologists figure out where life began. Could proteins, RNA or even biological cells have formed in the early Solar System within objects such as Bennu’s parent planetesimal? Or did complex biochemistry begin only on Earth once the base materials had been delivered from space?

“What is becoming very clear is that the basic chemical building blocks of life could have been delivered to Earth, where further chemical evolution could have occurred in a habitable environment, including the origin of life itself,” says Glavin.

What’s really needed are more samples. China’s Tianwen-2 mission is blasting off later this year on a mission to capture a 100 g sample from the small near-earth asteroid 469219 Kamo‘oalewa. The findings are likely to be similar to those of OSIRIS-REx and Hayabusa2, but there’s always the chance that something more complex might be in that sample too. If and when those organic molecules are found, they will have huge repercussions for the origin of life on Earth.

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“What makes a good astronaut?” asks director Hannah Berryman in the opening scene of Spacewoman. It’s a question few can answer better than Eileen Collins. As the first woman to pilot and command a NASA Space Shuttle, her career was marked by historic milestones, extraordinary challenges and personal sacrifices. Collins looks down the lens of the camera and, as she pauses for thought, we cut to footage of her being suited up in astronaut gear for the third time. “I would say…a person who is not prone to panicking.”

In Spacewoman, Berryman crafts a thoughtful, emotionally resonant documentary that traces Collins’s life from a determined young girl in Elmira, New York, to a spaceflight pioneer.

The film’s strength lies in its compelling balance of personal narrative and technical achievement. Through intimate interviews with Collins, her family and former colleagues, alongside a wealth of archival footage, Spacewoman paints a vivid portrait of a woman whose journey was anything but straightforward. From growing up in a working-class family affected by her parents’ divorce and Hurricane Agnes’s destruction, to excelling in the male-dominated world of aviation and space exploration, Collins’s resilience shines through.

Berryman wisely centres the film on the four key missions that defined Collins’s time at NASA. While this approach necessitates a brisk overview of her early military career, it allows for an in-depth exploration of the stakes, risks and triumphs of spaceflight. Collins’s pioneering 1995 mission, STS-63, saw her pilot the Space Shuttle Discovery in the first rendezvous with the Russian space station Mir, a mission fraught with political and technical challenges. The archival footage from this and subsequent missions provides gripping, edge-of-your-seat moments that demonstrate both the precision and unpredictability of space travel.

Perhaps Spacewoman’s most affecting thread is its examination of how Collins’s career intersected with her family life. Her daughter, Bridget, born shortly after her first mission, offers a poignant perspective on growing up with a mother whose job carried life-threatening risks. In one of the film’s most emotionally charged scenes, Collins recounts explaining the Challenger disaster to a young Bridget. Despite her mother’s assurances that NASA had learned from the tragedy, the subsequent Columbia disaster two weeks later underscores the constant shadow of danger inherent in space exploration.

These deeply personal reflections elevate Spacewoman beyond a straightforward biographical documentary. Collins’s son Luke, though younger and less directly affected by his mother’s missions, also shares touching memories, offering a fuller picture of a family shaped by space exploration’s highs and lows. Berryman’s thoughtful editing intertwines these recollections with historic footage, making the stakes feel immediate and profoundly human.

The film’s tension peaks during Collins’s final mission, STS-114, the first “return to flight” after Columbia. As the mission teeters on the brink of disaster due to familiar technical issues, Berryman builds a heart-pounding narrative, even for viewers unfamiliar with the complexities of spaceflight. Without getting bogged down in technical jargon, she captures the intense pressure of a mission fraught with tension – for those on Earth, at least.

Berryman’s previous films include Miss World 1970: Beauty Queens and Bedlam and Banned, the Mary Whitehouse Story. In a recent episode of the Physics World Stories podcast, she told me that she was inspired to make the film after reading Collins’s autobiography Through the Glass Ceiling to the Stars. “It was so personal,” she said, “it took me into space and I thought maybe we could do that with the viewer.” Collins herself joined us for that podcast episode and I found her to be that same calm, centred, thoughtful person we see in the film and who NASA clearly very carefully chose to command such an important mission.

Spacewoman isn’t just about near-misses and peril. It also celebrates moments of wonder: Collins describing her first sunrise from space or recalling the chocolate shuttles she brought as gifts for the Mir cosmonauts. These light-hearted anecdotes reveal her deep appreciation for the unique experience of being an astronaut. On the podcast, I asked Collins what one lesson she would bring from space to life on Earth. After her customary moment’s pause for thought, she replied “Reading books about science fiction is very important.” She was a fan of science fiction in her younger years , which enabled her to dream of the future that she realized at NASA and in space. But, she told me, these days she also reads about real science of the future (she was deep into a book on artificial intelligence when we spoke) and history too. Looking back at Collins’s history in space certainly holds lessons for us all.

Berryman’s directorial focus ultimately circles back to a profound question: how much risk is acceptable in the pursuit of human progress? Spacewoman suggests that those committed to something greater than themselves are willing to risk everything. Collins’s career embodies this ethos, defined by an unshakeable resolve, even in the face of overwhelming odds.

In the film’s closing moments, we see Collins speaking to a wide-eyed girl at a book signing. The voiceover from interviews talks of the women slated to be instrumental in humanity’s return to the Moon and future missions to Mars. If there’s one thing I would change about the film, it’s that the final word is given to someone other than Collins. The message is a fitting summation of her life and legacy, but I would like to have seen it delivered with her understated confidence of someone who has lived it. It’s a quibble though in a compelling film that I would recommend to anyone with an interest in space travel or the human experience here on Earth.

When someone as accomplished as Collins says that you need to work hard and practise, practise, practise it has a gravitas few others can muster. After all, she spent 10 years practising to fly the Space Shuttle – and got to do it for real twice. We see Collins speak directly to the wide-eyed girl in a flight suit as she signs her book and, as she does so, you can feel the words really hit home precisely because of who says them: “Reach for the stars. Don’t give up. Keep trying because you can do it.”

Spacewoman is more than a tribute to a trailblazer; it’s a testament to human perseverance, curiosity and courage. In Collins’s story, Berryman finds a gripping, deeply personal narrative that will resonate with audiences across the planet.

• Spacewoman premiered at DOC NYC in November 2024 and is scheduled for theatrical release in 2025. A Haviland Digital Film in association with Tigerlily Productions.

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Watch this short video filmed at the APS March Meeting in 2024, where Mark Elo, chief marketing officer of Tabor Quantum Solutions, introduces the Echo-5Q, which he explains is an industry collaboration between FormFactor and Tabor Quantum Solutions, using the QuantWare quantum processing unit (QPU).

Elo points out that it is an out-of-the-box solution, allowing customers to order a full-stack system, including the software, refrigeration, control electronics and the actual QPU. With the Echo-5, it gets delivered and installed, so that the customer can start doing quantum measurements immediately. He explains that the Echo-5Q is designed at a price and feature point that increases the accessibility for on-site quantum computing.

Brandon Boiko, senior applications engineer with FormFactor, describes the how FormFactor developed the dilution refrigeration technology that the qubits get installed into. Boiko explains that the product has been designed to reduce the cost of entry into the quantum field – made accessible through FormFactor’s test-and- measurement programme, which allows people to bring their samples on site to take measurements.

Alessandro Bruno is founder and CEO of QuantWare, which provides the quantum processor for the Echo-5Q, the part that sits at the milli Kelvin stage of the dilution refrigerator, and that hosts five qubits. Bruno hopes that the Echo-5Q will democratize access to quantum devices – for education, academic research and start-ups.

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As our world becomes ever more dependent on technology, an important question emerges: how much can we truly rely on that technology? To help researchers explore this question, IOP Publishing (which publishes Physics World) is launching a new peer-reviewed, open-access publication called Journal of Reliability Science and Engineering (JRSE). The journal will operate in partnership with the Institute of Systems Engineering (part of the China Academy of Engineering Physics) and will benefit from the editorial and commissioning support of the University of Electronic Science and Technology of China, Hunan University and the Beijing Institute of Structure and Environment Engineering.

“Today’s society relies much on sophisticated engineering systems to manufacture products and deliver services,” says JRSE’s co-editor-in-chief, Mingjian Zuo, a professor of mechanical engineering at the University of Alberta, Canada. “Such systems include power plants, vehicles, transportation and manufacturing. The safe, reliable and economical operation of all these requires the continuing advancement of reliability science and engineering.”

Defining reliability

The reliability of an object is commonly defined as the probability that it will perform its intended function adequately for a specified period of time. “The object in question may be a human being, product, system, or process,” Zuo explains. “Depending on its nature, corresponding sub-disciplines are human-, material-, structural-, equipment-, software- and system reliability.”

Key concepts in reliability science include failure modes, failure rates and reliability function and coherency, as well as measurements such as mean time-to-failure, mean time between failures, availability and maintainability. “Failure modes can be caused by effects like corrosion, cracking, creep, fracture, fatigue, delamination and oxidation,” Zuo explains.

To analyse such effects, researchers may use approaches such as fault tree analysis (FTA); failure modes, effects and criticality analysis (FMECA); and binary decomposition, he adds. These and many other techniques lie within the scope of JRSE, which aims to publish high-quality research on all aspects of reliability. This could, for example, include studies of failure modes and damage propagation as well as techniques for managing them and related risks through optimal design and reliability-centred maintenance.

A focus on extreme environments

To give the journal structure, Zuo and his colleagues identified six major topics: reliability theories and methods; physics of failure and degradation; reliability testing and simulation; prognostics and health management; reliability engineering applications; and emerging topics in reliability-related fields.

As well as regular issues published four times a year, JRSE will also produce special issues. A special issue on system reliability and safety in varying and extreme environments, for example, focuses on reliability and safety methods, physical/mathematical and data-driven models, reliability testing, system lifetime prediction and performance evaluation. Intelligent operation and maintenance of complex systems in varying and extreme environments are also covered.

Interest in extreme environments was one of the factors driving the journal’s development, Zuo says, due to the increasing need for modern engineering systems to operate reliably in highly demanding conditions. As examples, he cites wind farms being built further offshore; faster trains; and autonomous systems such as drones, driverless vehicles and social robots that must respond quickly and safely to ever-changing surroundings in close proximity to humans.

“As a society, we are setting ever higher requirements on critical systems such as the power grid and Internet, water distribution and transport networks,” he says. “All of these demand further advances in reliability science and engineering to develop tools for the design, manufacture and operation as well as the maintenance of today’s sophisticated engineering systems.”

The go-to platform for researchers and industrialists alike

Another factor behind the journal’s launch is that previously, there were no international journals focusing on reliability research by Chinese organizations. Since the discipline’s leaders include several such organizations, Zuo says the lack of international visibility has seriously limited scientific exchange and promotion of reliability research between China and the global community. He hopes the new journal will remedy this. “Notable features of the journal include gold open access (thanks to our partnership with IOP Publishing, a learned-society publisher that does not have shareholders) and a fast review process,” he says.

In general, the number of academic journals focusing on reliability science and engineering is limited, he adds. “JRSE will play a significant role in promoting the advances in reliability research by disseminating cutting-edge scientific discoveries and creative reliability assurance applications in a timely way.

“We are aiming that the journal will become the go-to platform for reliability researchers and industrialists alike.”

The first issue of JRSE will be published in March 2025, and its editors welcome submissions of original research reports as well as review papers co-authored by experts. “There will also be space for perspectives, comments, replies, and news insightful to the reliability community,” says Zuo. In the future, the journal plans to sponsor reliability-related academic forums and international conferences.

With over 100 experts from around the world on its editorial board, Zuo describes JRSE as scientist-led, internationally-focused and highly interdisciplinary. “Reliability is a critical measure of performance of all engineering systems used in every corner of our society,” he says. “This journal will therefore be of interest to disciplines such as mechanical-, electrical-, chemical-, mining- and aerospace engineering as well as the mathematical and life sciences.”

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The anomalous and ultra-low thermal expansion of cordierite results from the interplay between lattice vibrations and the elastic properties of the material. That is the conclusion of Martin Dove at China’s Sichuan University and Queen Mary University of London in the UK and Li Li at the Civil Aviation Flight University of China. They showed that the material’s unusual behaviour stems from direction-varying elastic forces in its lattice, which act to vary cordierite’s thermal expansion along different directions.

Cordierite is a naturally-occurring mineral that can also be synthesized. Thanks to its remarkable thermal properties, it is used in products ranging from pizza stones to catalytic converters. When heated to high temperatures, it undergoes ultra-low thermal expansion along two directions, and it shrinks a tiny amount along the third direction. This makes it incredibly useful as a material that can be heated and cooled without changing size or suffering damage.

Despite its widespread use, scientists lack a fundamental understanding of how cordierite’s anomalous thermal expansion arises from the properties of its crystal lattice. Normally, thermal expansion (positive or negative) is understood in terms of Grüneisen parameters. These describe how vibrational modes (phonons) in the lattice cause it to expand or contract along each axis as the temperature changes.

Negative Grüneisen parameters describe a lattice that shrinks when heated, and are seen as key to understanding thermal contraction of cordierite. However, the material’s thermal response is not isotropic (it only contracts only along one axis when heated at high temperatures) so understanding cordierite in terms of its Grüneisen parameters alone is difficult.

Advanced molecular dynamics

In their study, Dove and Li used advanced molecular dynamics simulations to accurately model the behaviour of atoms in the cordierite lattice. Their closely matched experimental observations of the material’s thermal expansion, providing them with key insights into why the material has a negative thermal expansion in just one direction.

“Our research demonstrates that the anomalous thermal expansion of cordierite originates from a surprising interplay between atomic vibrations and elasticity,” Dove explains. The elasticity is described in the form of an elastic compliance tensor, which predicts how a material will distort in response to a force applied along a specific direction.

At lower temperatures, lattice vibrations occur at lower frequencies. In this case, the simulations predicted negative thermal expansion in all directions – which is in line with observations of the material.

At higher temperatures, the lattice becomes dominated by high-frequency vibrations. In principle, this should result in positive thermal expansion in all three directions. Crucially, however, Dove and Li discovered that this expansion is cancelled out by the material’s elastic properties, as described by its elastic compliance tensor.

What is more, the unique arrangement of crystal lattice meant that this tensor varied depending on the direction of the applied force, creating an imbalance that amplifies differences between the material’s expansion along each axis.

Cancellation mechanism

“This cancellation mechanism explains why cordierite exhibits small positive expansion in two directions and small negative expansion in the third,” Dove explains. “Initially, I was sceptical of the results. The initial data suggested uniform expansion behaviour at both high and low temperatures, but the final results revealed a delicate balance of forces. It was a moment of scientific serendipity.”

Altogether, Dove and Li’s result clearly shows that cordierite’s anomalous behaviour cannot be understood by focusing solely on the Grüneisen parameters of its three axes. It is crucial to take its elastic compliance tensor into account.

In solving this long-standing mystery, the duo now hope their results could help researchers to better predict how cordierite’s thermal expansion will vary at different temperatures. In turn, they could help to extend the useful applications of the material even further.

“Anisotropic materials like cordierite hold immense potential for developing high-performance materials with unique thermal behaviours,” Dove says. “Our approach can rapidly predict these properties, significantly reducing the reliance on expensive and time-consuming experimental procedures.”

The research is described in Matter.

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A new way to measure the temperatures of objects by studying the effect of their black-body radiation on Rydberg atoms has been demonstrated by researchers at the US National Institute of Standards and Technology (NIST). The system, which provides a direct, calibration-free measure of temperature based on the fact that all atoms of a given species are identical, has a systematic temperature uncertainty of around 1 part in 2000.

The black-body temperature of an object is defined by the spectrum of the photons it emits. In the laboratory and in everyday life, however, temperature is usually measured by comparison to a reference. “Radiation is inherently quantum mechanical,” says NIST’s Noah Schlossberger, “but if you go to the store and buy a temperature sensor that measures the radiation via some sort of photodiode, the rate of photons converted into some value of temperature that you see has to be calibrated. Usually that’s done using some reference surface that’s held at a constant temperature via some sort of contact thermometer, and that contact thermometer has been calibrated to another contact thermometer – which in some indirect way has been tied into some primary standard at NIST or some other facility that offers calibration services.” However, each step introduces potential error.

This latest work offers a much more direct way of determining temperature. It involves measuring the black-body radiation emitted by an object directly, using atoms as a reference standard. Such a sensor does not need calibration because quantum mechanics dictates that every atom of the same type is identical. In Rydberg atoms the electrons are promoted to highly excited states. This makes the atoms much larger, less tightly bound and more sensitive to external perturbations. As part of an ongoing project studying their potential to detect electromagnetic fields, the researchers turned their attention to atom-based thermometry. “These atoms are exquisitely sensitive to black-body radiation,” explains NIST’s Christopher Holloway, who headed the work.

Packet of rubidium atoms

Central to the new apparatus is a magneto-optical trap inside a vacuum chamber containing a pure rubidium vapour. Every 300 ms, the researchers load a new packet of rubidium atoms into the trap, cool them to around 1 mK and excite them from the 5S energy level to the 32S Rydberg state using lasers. They then allow them to absorb black-body radiation from the surroundings for around 100 μs, causing some of the 32S atoms to change state. Finally, they apply a strong, ramped electric field, ionizing the atoms. “The higher energy states get ripped off easier than the lower energy states, so the electrons that were in each state arrive at the detector at a different time. That’s how we get this readout that tells us the population in each of the states,” explains Schlossberger, the work’s first author. The researchers can use this ratio to infer the spectrum of the black-body radiation absorbed by the atoms and, therefore, the temperature of the black body itself.

The researchers calculated the fractional systematic uncertainty of their measurement as 0.006, which corresponds to around 2 K at room temperature. Schlossberger concedes that this sounds relatively unimpressive compared to many commercial thermometers, but he notes that their thermometer measures absolute temperature, not relative temperature. “If I had two skyscrapers next to each other, touching, and they were an inch different in height, you could probably measure that difference to less than a millimetre,” he says, “If I asked you to tell me the total height of the skyscraper, you probably couldn’t.”

One application of their system, the researchers say, could lie in optical clocks, where frequency shifts due to thermal background noise are a key source of uncertainty. At present, researchers have to perform a lot of in situ thermometry to try to infer the black-body radiation experienced by the clock without disturbing the clock itself. Schlossberger says that, in future, one additional laser, could potentially allow the creation of Rydberg states in the clock atoms. “It’s sort of designed so that all the hardware is the same as atomic clocks, so without modifying the clock significantly it would tell you the radiation experienced by the same atoms that are used in the clock in the location they’re used.”

The work is described in a paper in Physical Review Research. Atomic physicist Kevin Weatherill of Durham University in the UK says “it’s an interesting paper and I enjoyed reading it”. “The direction of travel is to look for a quantum measurement for temperature – there are a lot of projects going on at NIST and some here in the UK,”, he says. He notes, however, that this experiment is highly complex and says “I think at the moment just measuring the width of an atomic transition in a vapour cell [which is broadened by the Doppler effect as atoms move faster] gives you a better bound on temperature than what’s been demonstrated in this paper.”

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What skills do you use every day in your job?

I am one of two co-chairs, along with my colleague Hendrik Ohldag, of the Quantum Materials Research and Discovery Thrust Area at ALS. Among other things, our remit is to advise ALS management on long-term strategy regarding quantum science, We launch and manage beamline development projects to enhance the quantum research capability at ALS and, more broadly, establish collaborations with quantum scientists and engineers in academia and industry.

In terms of specifics, the thrust area addresses problems of condensed-matter physics related to spin and quantum properties – for example, in atomically engineered multilayers, 2D materials and topological insulators with unusual electronic structures. As a beamline scientist, active listening is the key to establishing productive research collaborations with our scientific end-users – helping them to figure out the core questions they’re seeking to answer and, by extension, the appropriate experimental techniques to generate the data they need.

The task, always, is to translate external users’ scientific goals into practical experiments that will run reliably on the ALS beamlines. High-level organizational skills, persistence and exhaustive preparation go a long way: it takes a lot of planning and dialogue to ensure scientific users get high-quality experimental results.

What do you like best and least about your job?

A core part of my remit is to foster the collective conversation between ALS staff scientists and the quantum community, demystifying synchrotron science and the capabilities of the ALS with prospective end-users. The outreach activity is exciting and challenging in equal measure – whether that’s initiating dialogue with quantum experts at scientific conferences or making first contact using Teams or Zoom.

Internally, we also track the latest advances in fundamental quantum science and applied R&D. In-house colloquia are mandatory, with guest speakers from the quantum community engaging directly with ALS staff teams to figure out how our portfolio of synchrotron-based techniques – whether spectroscopy, scattering or imaging – can be put to work by users from research or industry. This learning and development programme, in turn, underpins continuous improvement of the beamline support services we offer to all our quantum end-users.

As for downsides: it’s never ideal when a piece of instrumentation suddenly “breaks” on a Friday afternoon. This sort of troubleshooting is probably the part of the job I like least, though it doesn’t happen often and, in any case, is a hit I’m happy to take given the flexibility inherent to my role.

What do you know today that you wish you knew when you were starting out in your career?

It’s still early days, but I guess the biggest lesson so far is to trust in my own specialist domain knowledge and expertise when it comes to engaging with the diverse research community working on quantum materials. My know-how in photon science – from coherent X-ray scattering and X-ray detector technology to in situ magnetic- and electric-field studies and automated measurement protocols – enables visiting researchers to get the most out of their beamtime at ALS.

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Radiation therapy is a targeted cancer treatment that’s typically delivered over several weeks, using a plan that’s optimized on a CT scan taken before treatment begins. But during this time, the geometry of the tumour and the surrounding anatomy can vary, with different patients responding in different ways to the delivered radiation. To optimize treatment quality, such changes must be taken into consideration. And this is where adaptive radiotherapy comes into play.

Adaptive radiotherapy uses patient images taken throughout the course of treatment to update the initial plan and compensate for any anatomical variations. By adjusting the daily plan to match the patient’s daily anatomy, adaptive treatments ensure more precise, personalized and efficient radiotherapy, improving tumour control while reducing toxicity to healthy tissues.

The implementation of adaptive radiotherapy is continuing to expand, as technology developments enable adaptive treatments in additional tumour sites. And as more cancer centres worldwide choose this approach, there’s a need for flexible, innovative software to streamline this increasing clinical uptake.

Designed to meet these needs, RayStation – the treatment planning system from oncology software specialist RaySearch Laboratories – makes adaptive radiotherapy faster and easier to implement in clinical practice. The versatile and holistic RayStation software provides all of the tools required to support adaptive planning, today and into the future.

“We need to be fast, we need to be predictable and we need to be user friendly,” says Anna Lundin, technical product manager at RaySearch Laboratories.

Meeting the need for speed

Typically, adaptive radiotherapy uses the cone-beam CT (CBCT) images acquired for daily patient positioning to perform plan adaptation. For seamless implementation into the clinical workflow to fully reflect the daily anatomical changes, this procedure should be performed “online” with the patient on the treatment table, as opposed to an “offline” approach where plan adaptation occurs after the patient has left the treatment session. Such online adaptation, however, requires the ability to analyse patient scans and perform adaptive re-planning as rapidly as possible.

To fulfil the needs for streamlining all types of adaptive (online or offline) requirements, RayStation incorporates a package of advanced algorithms that perform key tasks, including segmentation, deformable registration, CBCT image enhancement and recontouring, all while the previously delivered dose is taken into consideration. By automating all of these steps, RayStation accelerates the replanning process to the speed needed for online adaptation, with the ability to create an adaptive plan in less than a minute.

Central to this process is RayStation’s dose tracking, which uses the daily images to calculate the actual dose delivered to the patient in each fraction. This ability to evaluate treatment progress, both on a daily basis and considering the estimated total dose, enables informed decisions as to whether to replan or not. The software’s flexible workflow allows users to perform daily dose tracking, compare plans with daily anatomical information against the original plans and adapt when needed.

“You can document trigger points for when adaptation is needed,” Lundin explains. “So you can evaluate whether the original plan is still good to go or whether you want to update or adapt the treatment plan to changes that have occurred.”

User friendly

Another challenge when implementing online adaptation is that its time constraints necessitate access to intuitive tools that enable quick decision making. “One of the big challenges with adaptive radiotherapy has been that a lot of the decision making and processes have been done on an ad hoc basis,” says Lundin. “We need to utilize the same protocol-based planning for adaptive as we do for standard treatment planning.”

As such, RaySearch Laboratories has focused on developing software that’s easy to use, efficient and accessible to a large proportion of clinical personnel. RayStation enables clinics to define and validate clinical procedures for a specific patient category in advance, eliminating the need to repeat this each time.

“By doing this, we let the clinicians focus on what they do best – taking responsibility for the clinical decisions – while RayStation focuses on providing all the data that they need to make that possible,” Lundin adds.

Versatile design

Lundin emphasizes that this accelerated adaptive replanning solution is built upon RayStation’s pre-existing comprehensive framework. “It’s not a parallel solution, it’s a progression,” she explains. “That means that all the tools that we have for robust optimization and evaluation, tools to assess biological effects, support for multiple treatment modalities – all that is also available when performing adaptive assessments and adaptive planning.”

This flexibility allows RayStation to support both photon- and ion-based treatments, as well as multiple imaging modalities. “We have built a framework that can be configured for each site and each clinical indication,” says Lundin. “We believe in giving users the freedom to select which techniques and which strategies to employ.”

We let the clinicians focus on what they do best – taking responsibility for the clinical decisions – while RayStation focuses on providing all the data that they need to make that possible

In particular, adaptive radiotherapy is gaining interest among the proton therapy community. For such highly conformal treatments, it’s even more important to regularly assess the actual delivered dose and ensure that the plan is updated to deliver the correct dose each day. “We have the first clinics using RayStation to perform adaptive proton treatments in an online fashion,” Lundin says.

It’s likely that we will also soon see the emergence of biologically adapted radiotherapy, in which treatments are adapted not just to the patient’s anatomy, but to the tumour’s biological characteristics and biological response. Here again, RayStation’s flexible and holistic architecture can support the replanning needs of this advanced treatment approach.

Predictable performance

Lundin points out that the progression towards online adaptation has been valuable for radiotherapy as a whole. “A lot of the improvements required to handle the time-critical procedures of online adaptive are of large benefit to all adaptive assessments,” she explains. “Fast and predictable replanning is crucial to allow us to treat more patients with greater specificity using less clinical resources. I see it as strictly necessary for online adaptive, but good for all.”

Artificial intelligence (AI) is not only a key component in enhancing the speed and consistency of treatment planning (with tools such as deep learning segmentation and planning), but also enables the handling of massive data sets, which in turn allows users to improve the treatment “intents” that they prescribe.

Learning more about how the delivered dose correlates with clinical outcome provides important feedback on the performance and effectiveness of current adaptive processes. This will help optimize and personalize future treatments and, ultimately, make the adaptive treatments more predictable and effective as a whole.

Lundin explains that full automation is the only way to generate the large amount of data in the predictable and consistent manner required for such treatment advancements, noting that it is not possible to achieve this manually.

RayStation’s ability to preconfigure and automate all of the steps needed for daily dose assessment enables these larger-scale dose follow-up clinical studies. The treatment data can be combined with patient outcomes, with AI employed to gain insight into how to best design treatments or predict how a tumour will respond to therapy.

“I look forward to seeing more outcome-related studies of adaptive radiotherapy, so we can learn from each other and have more general recommendations, as has been done in the field of standard radiotherapy planning,” says Lundin. “We need to learn and we need to improve. I think that is what adaptive is all about – to adapt each person’s treatment, but also adapt the processes that we use.”

Future evolution

Looking to the future, adaptive radiotherapy is expected to evolve rapidly, bolstered by ongoing advances in imaging techniques and increasing data processing speeds. RayStation’s machine learning-based segmentation and plan optimization algorithms will continue to play a central role in supporting this evolution, with AI making treatment adaptations more precise, personalized and efficient, enhancing the overall effectiveness of cancer treatment.

“RaySearch, with the foundation that we have in optimization and advancing treatment planning and workflows, is very well equipped to take on the challenges of these future developments,” Lundin adds. “We are looking forward to the improvements to come and determined to meet the expectations with our holistic software.”

• Get to know RaySearch’s oncology information system, RayCare, and explore the role it plays in adaptive radiotherapy.

The post Fast and predictable: RayStation meets the needs of online adaptive radiotherapy appeared first on Physics World.

This webinar will present the overall experience of a radiotherapy department that utilizes RTsafe QA solutions, including the RTsafe Prime and SBRT anthropomorphic phantoms for intracranial stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) applications, respectively, as well as the remote dosimetry services offered by RTsafe. The session will explore how these phantoms can be employed for end-to-end QA measurements and dosimetry audits in both conventional linacs and a Unity MR-Linac system. Key features of RTsafe phantoms, such as their compatibility with RTsafe’s remote dosimetry services for point (OSLD, ionization chamber), 2D (films), and 3D (gel) dosimetry, will be discussed. These capabilities enable a comprehensive SRS/SBRT accuracy evaluation across the entire treatment workflow – from imaging and treatment planning to dose delivery.

Christopher Schneider is the adaptive radiotherapy technical director at Mary Bird Perkins Cancer Center and serves as an adjunct assistant professor in the Department of Physics and Astronomy at Louisiana State University in Baton Rouge. Under his supervision, Mary Bird’s MR-guided adaptive radiotherapy program has provided treatment to more than 150 patients in its first year alone. Schneider’s research group focuses on radiation dosimetry, late effects of radiation, and the development of radiotherapy workflow and quality-assurance enhancements.

The post Enhancing SRS/SBRT accuracy with RTsafe QA solutions: An overall experience appeared first on Physics World.

Solution

Black body radiation, spectral density: ε (ν) dν = hνρ (ν) n (ν)

The photon energy, E = hν where h is Planck’s constant and ν is the photon frequency.

The density of states, ρ (ν) = Aνⁿ⁻¹ where A is a constant independent of the frequency and the frequency term is the scaling of surface area of an n-dimensional sphere.

The Bose–Einstein distribution,

n(v)$=\frac{1}{e\frac{hv}{kT}-1}$

where k is the Boltzmann constant and T is the temperature.

We let

$x=\frac{hv}{kT}$

and get

ε(x)$\propto =\frac{x^n}{e^x-1}$

We do not need the constant of proportionality (which is not simple to calculate in 4D) to find the maximum of ε (x). Working out the constant just tells us how tall the peak is, but we are interested in where the peak is, not the total radiation.

$\frac{d\epsilon }{dx}\propto \frac{n{x}^{n-1}}{e^x-1}-\frac{x^n{e}^x}{{\left(e^x-1\right)}^2}$

We set this equal to zero for the maximum of the distribution,

$\frac{x^{n-1}{e}^x}{{\left(e^x-1\right)}^2}\left(n\left(1-e^{-x}\right)-x\right)=0$

This yields x = n (1 − e^−x) where

$x=\frac{h{v}_{max}}{kT}$

and we can relate

${\lambda }_{max}=\frac{c}{v_{max}}$

and c being the speed of light.

This equation has the solution x = n +W (−ne⁻ⁿ) where W is the Lambert W function z = W (y) that solves ze^z = y (although there is a subtlety about which branch of the function). This is kind of useless to do anything with, though. One can numerically solve this equation using bisection/Newton–Raphson/iteration. Alternatively, one could notice that as the number of dimensions increases, e^−x is small, so to leading approximation x ≈ n. One can do a little better iterating this, x ≈ n − ne⁻ⁿ which is what we will use. Note the second iteration yields

$x\approx n-n{e}^{\left(n-n{e}^{-n}\right)}$

Number of dimensions, n	Numerical solution	Approximation
2	1.594	1.729
3	2.821	2.851
4 (the one we want)	3.921	3.927
5	4.965	4.966
6	5.985	5.985

Using the result above,

${\lambda }_{max}=\frac{hc}{kT{x}_{max}}=\frac{6.63 \times {10}^{-34}·3\times {10}^8}{1.38\times {10}^{-23}·6\times {10}^3·3.9}=616 nm$

616 nm is middle of the spectrum, so it will look white with a green-blue tint. Note, we have used T = 6000 K for the temperature here, as given in the question.

It would also be valid to look at ε (λ) dλ instead of ε (ν) dν.

Solution

First we will set up the equations of motion for our system. We will set one mass to be at position −x and the other to be at x, so the masses are at a distance of 2x from each other. Starting from Newton’s law of gravity:

$F=-\frac{G{m}^2}{{\left(2x\right)}^2}$

we can then use Newton’s second law to rewrite the LHS,

$m\ddot{x}=-\frac{G{m}^2}{4x^2}$

which we can simplify to

$\ddot{x}=-\frac{Gm}{4x^2}$

It is important that you get the right factor here depending on your choice for the particle coordinates at the start. Note there are other methods of getting this point, e.g. reduced mass.

We can now solve the second order ODE above. We will not show the whole process here but present the starting point and key results. We can write the acceleration in terms of the velocity. The initial velocity is zero and the initial position

$x_i=\frac{d}{2}$

So,

$v\frac{dv}{dx}=-\frac{Gm}{4x^2}\to \underset{0}{\overset{v}{\int }}vdv=-\frac{Gm}{4}\underset{x_i}{\overset{x}{\int }}\frac{dx}{x^2}$

and once the integrals are solved we can rearrange for the velocity,

$v=\frac{dx}{dt}=-\sqrt{\frac{Gm}{2}}\sqrt{\frac{1}{x}-\frac{1}{x_i}}$

Now we can form an expression for the total time taken for the masses to meet in the middle,

$T=\sqrt{\frac{2}{Gm}}\underset{0}{\overset{x_i}{\int }}\frac{dx}{\sqrt{\frac{1}{x}-\frac{1}{x_i}}}$

There are quite a few steps involved in solving this integral, for these solutions, we shall make use of the following (but do attempt to solve it for yourselves in full).

$\underset{0}{\overset{1}{\int }}\sqrt{\frac{y}{1-y}}dy=si{n}^{-1}\left(1\right)=\frac{\pi }{2}$

Hence,

$T=\frac{\pi }{2}\sqrt{\frac{2x_i^3}{Gm}}=\frac{\pi }{2}\sqrt{\frac{d^3}{4Gm}}$

We can now rearrange for G and substitute in the values given in the question, don’t forget to convert the time into seconds.

$G=\frac{d^3}{4m}{\left(\frac{\pi }{2T}\right)}^2=6.67\times {10}^{-11} m^{3}k{g}^{-1}{s}^{-2}$

This is the generally accepted value for the gravitational constant of our universe as well.

Solution

We will write the period of oscillation of the pendulum at the surface of the Earth to be

$T_0=2\pi \sqrt{\frac{l}{g_0}}$.

At a height h above the surface of the Earth the period of oscillation will be

$T_h=2\pi \sqrt{\frac{l}{g_h}}$,

where g₀ and g_h are the acceleration due to gravity at the surface of the Earth and a height h above it respectively.

We can define τ₀ to be the total duration of the day which is 8.64 × 10⁴ seconds and equal to N complete oscillations of the pendulum at the surface. The lag is then τ_h which will equal N times the difference in one period of the two clocks, τ_h = NΔT, where ΔT = (T_h − T₀). We can now take a ratio of the lag over the day and the total duration of the day:

$\frac{{\tau }_h}{{\tau }_0}=\frac{N\left(T_h-T_0\right)}{N{T}_0}\Rightarrow {\tau }_h={\tau }_0\frac{T_h-T_0}{T_0}={\tau }_h={\tau }_0\left(\frac{T_h}{T_0}-1\right)$

Then by substituting in the expressions we have for the period of a pendulum at the surface and height h we can write this in terms of the gravitational constant,

${\tau }_h={\tau }_0\left(\sqrt{\frac{g_0}{g_h}}-1\right)$

[Award 1 mark for finding the ratio of the lag over the day and the total period of the day.]

The acceleration due to gravity at the Earth’s surface is

$g_0=\frac{GM}{R^2}$

where G is the universal gravitational constant, M is the mass of the Earth and R is the radius of the Earth. At an altitude h, it will be

$g_h=\frac{GM}{{\left(R+h\right)}^2}$

[Award 1 mark for finding the expression for the acceleration due to gravity at height h.]

Substituting into our expression for the lag, we get:

${\tau }_h={\tau }_0\left(\sqrt{\frac{{\left(R+h\right)}^2}{R^2}}-1\right)={\tau }_0\left(\sqrt{1+\frac{2h}{R}+\frac{h^2}{R^2}}-1\right)={\tau }_0\left(\frac{\sqrt{R^2+2hR+h^2}}{R}-1\right)={\tau }_0\left(\frac{R+h}{R}-1\right)$

This simplifies to an expression for the lag over a day. We can then substitute in the given values to find,

${\tau }_h=\frac{{\tau }_{0}h}{R}=\frac{8.64\times {10}^4 s·300 m}{8.3781\times {10}^6 m} =4.064 s\approx 4 s$

[Award 2 marks for completing the simplification of the ratio and finding the lag to be ≈ 4 s.]

Solution

We can imagine this as an inverted pendulum, with gravity acting from the centre of mass $\left(\frac{l}{2}\right)$ and at an angle θ from the unstable equilibrium point.

[Award 1 mark for a suitable diagram of the system.]

We must now find the equations of motion of the system. For this we can use Newton’s second law $\overrightarrow{F}=m\overrightarrow{a}$ in its rotational form τ = Iα (torque = moment of inertia × angular acceleration). We have another equation for torque we can use as well

$\overrightarrow{\tau }=\overrightarrow{r}\times \overrightarrow{F}=\left|\overrightarrow{r}\right|\left|\overrightarrow{F}\right|\sin \theta \widehat{n}$

where r is the distance from the pivot to the centre of mass $\left(\frac{l}{2}\right)$ and F is the force, which in this case is gravity mg. We can then equate these giving

$\left|\overrightarrow{r}\right|\left|\overrightarrow{F}\right|\sin \theta =I\alpha$

Substituting in the given moment of inertia of the stick and that the angular acceleration

$\alpha =\frac{{\delta }^2\theta }{\delta t^2}=\ddot{\theta }$

We can cancel a few things and rearrange to get a differential equation of the form:

$\ddot{\theta }-\frac{3g}{2l}\sin \theta =0$

we then can take the small angle approximation sin θ ≈ θ, resulting in

$\ddot{\theta }-\frac{3g}{2l}\theta =0$

[Award 2 marks for finding the equation of motion for the system and using the small angle approximation.]

Solve with ansatz of θ = Ae^ωt + Be^−ωt, where we have chosen

${\omega }^2=\frac{3g}{2l}$

We can clearly see that this will satisfy the differential equation

$\dot{\theta }=\omega A{e}^{\omega t}-\omega B{e}^{-\omega t} and \ddot{\theta }={\omega }^{2}A{e}^{\omega t}+{\omega }^{2}B{e}^{-\omega t}$

Now we can apply initial conditions to find A and B, by looking at the two cases from the uncertainty principle

$\Delta x\Delta p=\Delta xm\Delta v\frac{\hslash }{2}$

Case 1: The stick is at an angle but not moving

At t = 0, θ = Δθ

θ = Δθ = A + B

At t = 0, $\dot{\theta }=0$

$\dot{\theta }=0=\omega A{e}^{{\omega }_0}-\omega B{e}^{-{\omega }_0}$, A=B

This implies Δθ = 2A and we can then find

$A=\frac{\Delta \theta }{2}=\frac{2\Delta x}{2l}=\frac{\Delta x}{l}$

So we can now write

$\theta =A\left(e^{\omega t}-e^{-\omega t}\right)=\frac{\Delta v}{\omega }\left(e^{\omega t}-e^{-\omega t}\right)$ or $\theta =\frac{2\Delta v}{\omega l}\sin h \omega t$

Case 2: The stick is at upright but moving

At t = 0, θ = 0

This condition gives us A = −B.

At t = 0, $\ddot{\theta }=\frac{2v}{l}$

This initial condition has come from the relationship between the tangential velocity, Δv which equals the distance to the centre of mass from the pivot point, $\frac{l}{2}$ and the angular velocity $\dot{\theta }$. Using the above initial condition gives us $\dot{\theta }=2\omega A$ where $A=\frac{\Delta v}{\omega l}$

We can now write

$\theta =A\left(e^{\omega t}-e^{-\omega t}\right)=\frac{\Delta v}{\omega }\left(e^{\omega t}-e^{-\omega t}\right) or \theta =\frac{2\Delta v}{\omega l}\sinh \omega t$

[Award 4 marks for finding the two expressions for θ by using the two cases of the uncertainty principle.]

Now there are a few ways we can finish off this problem, we shall look at three different ways. In each case when the stick has fallen on the ground $\theta \left(t_f\right)=\frac{\pi }{2}$.

Method 1

Take $\theta =\frac{2\Delta x}{l}\cosh \omega t$ and $\theta =\frac{2\Delta v}{\omega l}\sinh \omega t$, use $\theta \left(t_f\right)=\frac{\pi }{2}$ then rearrange for t_f in both cases. We have

$t_f=\frac{1}{\omega }\cos h{}^{-1}\frac{\pi l}{4\Delta x} and t_f=\frac{1}{\omega }\sinh {}^{-1}\frac{\pi \omega l}{4\Delta v}$

Look at the expression for cosh⁻¹ x and sinh⁻¹ x given in the question. They are almost identical, we can then approximate the two arguments to each other and we find,

$\Delta x=\frac{\Delta v}{\omega }$

we can then substitute in the uncertainty principle $\Delta x\Delta p=\frac{\hslash }{2}$ as $\Delta v=\frac{\hslash }{2m\delta x}$ and then write an expression of $\Delta x=\sqrt{\frac{\hslash }{2m\omega }}$, which we can put back into our arccosh expression (or do it for Δv and put into arcsinh).

$t_f=\frac{1}{\omega }\cosh {}^{-1}\frac{\pi l}{4\Delta x}$

where $\Delta x=\sqrt{\frac{\hslash }{2m\omega }}$ and $\omega =\sqrt{\frac{3g}{2l}}$.

Method 2

In this next method, when you get to the inverse hyperbolic functions, you can take an expansion of their natural log forms in the tending to infinity limit. To first order both functions give ln 2x, we can then equate the arguments and find Δx or Δv in terms of the other and use the uncertainty principle. This would give the time taken as,

$t_f=\frac{1}{\omega }\ln \frac{\pi l}{2\Delta x}$

where $\Delta x=\sqrt{\frac{\hslash }{2m\omega }}$ and $\omega =\sqrt{\frac{3g}{2l}}$.

Method 3

Rather than using hyperbolic functions, you could do something like above and do an expansion of the exponentials in the two expressions for t_f or we could make life even easier and do the following.

Disregard the e^−ωt terms as they will be much smaller than the e^ωt terms. Equate the two expressions for $\theta \left(t_f\right)=\frac{\pi }{2}$ and then take the natural logs, once again arriving at an expression of

$t_f=\frac{1}{\omega }\ln \frac{\pi l}{2\Delta x}$

where $\Delta x=\sqrt{\frac{\hslash }{2m\omega }}$ and $\omega =\sqrt{\frac{3g}{2l}}$.

This method efficiently sets B = 0 when applying the initial conditions.

[Award 2 marks for reaching an expression for t using one of the methods above or a suitable alternative that gives the correct units for time.]

Then, by using one of the expressions above for time, substitute in the values and find that t = 10.58 seconds.

[Award 1 mark for finding the correct time value of t = 10.58 seconds.]

• If you’re a student who wants to sign up for the 2025 edition of PLANCKS UK and Ireland, entries are now open at plancks.uk

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Oil spills can pollute large volumes of surrounding water – thousands of times greater than the spill itself – causing long-term economic, environmental, social and ecological damage. Effective methods for in situ capture of spilled oil are thus essential to minimize contamination from such disasters.

Many oil spill cleanup technologies, however, exhibit poor hydrodynamic stability under complex flow conditions, which leads to poor oil-capture efficiency. To address this shortfall, researchers from Harbin Institute of Technology in China have come up with a new approach to oil cleanup using a vortex-anchored filter (VAF).

“Since the 1979 Atlantic Empress disaster, interception and adsorption have been the primary methods for oil spill recovery, but these are sensitive to water-flow fluctuation,” explains lead author Shijie You. Oil-in-water emulsions from leaking pipelines and offshore industrial discharge are particularly challenging, says You, adding that “these problems inspire us to consider how we can address hydrodynamic stability of oil-capture devices under turbulent conditions”.

Inspired by the natural world

You and colleagues believe that the answers to oil spill challenges could come from nature – arguably the world’s greatest scientist. They found that the deep-sea glass sponge E. aspergillum, which lives at depths of up to 1000 m in the Pacific Ocean, has an excellent ability to filter feed with a high effectiveness, selectivity and robustness, and that its food particles share similarities with oil droplets.

The anatomical structure of E. aspergillum – also known as Venus’ flower basket – provided inspiration for the researchers to design their VAF. By mimicking the skeletal architecture and filter feeding patterns of the sponge, they created a filter that exhibited a high mass transfer and hydrodynamic stability in cleaning up oil spills under turbulent flow.

“The E. aspergillum has a multilayered skeleton–flagellum architecture, which creates 3D streamlines with frequent collision, deflection, convergence and separation,” explains You. “This can dissipate macro-scale turbulent flows into small-scale swirling flow patterns called low-speed vortical flows within the body cavity, which reduces hydrodynamic load and enhances interfacial mass transfer.”

For the sponges, this allows them to maintain a high mechanical stability while absorbing nutrients from the water. The same principles can be applied to synthetic materials for cleaning up oil spills.

The VAF is a synthetic form of the sponge’s architecture and, according to You, “is capable of transferring kinematic energy from an external water flow into multiple small-scale low-speed vortical flows within the body cavity to enhance hydrodynamic stability and oil capture efficiency”.

The tubular outer skeleton of the VAF comprises a helical ridge and chequerboard lattice. It is this skeleton that creates a slow vortex field inside the cavity and enables mass transfer of oil during the filtering process. Once the oil has been forced into the filter, the internal area – composed of flagellum-shaped adsorbent materials – provides a large interfacial area for oil adsorption.

Using the VAF to clean up oil spills

The researchers used their nature-inspired VAF to clean up oil spills under complex hydrodynamic conditions. You states that “the VAF can retain the external turbulent-flow kinetic energy in the low-speed vortical flows – with a small Kolmogorov microscale (85 µm) [the size of the smallest eddy in a turbulent flow] – inside the cavity of the skeleton, leading to enhanced interfacial mass transfer and residence time”.

“This led to an improvement in the hydrodynamic stability of the filter compared to other approaches by reducing the Reynolds stresses in nearly quiescent wake flows,” You explains. The filter was also highly resistant to bending stresses caused at the boundary of the filter when trying separate viscous fluids. When put into practice, the VAF was able to capture more than 97% of floating, underwater and emulsified oils, even under strong turbulent flow.

When asked how the researchers plan to improve the filter further, You tells Physics World that they “will integrate the VAF with photothermal, electrothermal and electrochemical modules for environmental remediation and resource recovery”.

“We look forward to applying VAF-based technologies to solve sea pollution problems with a filter that has an outstanding flexibility and adaptability, easy-to-handle operability and scalability, environmental compatibility and life-cycle sustainability,” says You.

The research is published in Nature Communications.

The post Filter inspired by deep-sea sponge cleans up oil spills appeared first on Physics World.

A topological electronic crystal (TEC) in which the quantum Hall effect emerges without the need for an external magnetic field has been unveiled by an international team of physicists. Led by Josh Folk at the University of British Columbia, the group observed the effect in a stack of bilayer and trilayer graphene that is twisted at a specific angle.

In a classical electrical conductor, the Hall voltage and its associated resistance appear perpendicular both to the direction of an applied electrical current and an applied magnetic field. A similar effect is also seen in 2D electron systems that have been cooled to ultra-low temperatures. But in this case, the Hall resistance becomes quantized in discrete steps.

This quantum Hall effect can emerge in electronic crystals, also known as Wigner crystals. These are arrays of electrons that are held in place by their mutual repulsion. Some researchers have considered the possibility of a similar effect occurring in structures called TECs, but without an applied magnetic field. This is called the “quantum anomalous Hall effect”.

Anomalous Hall crystal

“Several theory groups have speculated that analogues of these structures could emerge in quantized anomalous Hall systems, giving rise to a type of TEC termed an ‘anomalous Hall crystal’,” Folk explains. “This structure would be insulating, due to a frozen-in electronic ordering in its interior, with dissipation-free currents along the boundary.”

For Folk’s team, the possibility of anomalous hall crystals emerging in real systems was not the original focus of their research. Initially, a team at the University of Washington had aimed to investigate the diverse phenomena that emerge when two or more flakes of graphene are stacked on top of each other, and twisted relative to each other at different angles

While many interesting behaviours emerged from these structures, one particular stack caught the attention of Washington’s Dacen Waters, which inspired his team to get in touch with Folk and his colleagues in British Columbia.

In a vast majority of cases, the twisted structures studied by the team had moiré patterns that were very disordered. Moiré patterns occur when two lattices are overlaid and rotated relative to each other. Yet out of tens of thousands of permutations of twisted graphene stacks, one structure appeared to be different.

Exceptionally low levels of disorder

“One of the stacks seemed to have exceptionally low levels of disorder,” Folk describes. “Waters shared that one with our group to explore in our dilution refrigerator, where we have lots of experience measuring subtle magnetic effects that appear at a small fraction of a degree above absolute zero.”

As they studied this highly ordered structure, the team found that its moiré pattern helped to modulate the system’s electronic properties, allowing a TEC to emerge.

“We observed the first clear example of a TEC, in a device made up of bilayer graphene stacked atop trilayer graphene with a small, 1.5° twist,” Folk explains. “The underlying topology of the electronic system, combined with strong electron-electron interactions, provide the essential ingredients for the crystal formation.”

After decades of theoretical speculation, Folk, Waters and colleagues have identified an anomalous Hall crystal, where the quantum Hall effect emerges from an in-built electronic structure, rather than an applied magnetic field.

Beyond confirming the theoretical possibility of TECs, the researchers are hopeful that their results could lay the groundwork for a variety of novel lines of research.

“One of the most exciting long-term directions this work may lead is that the TEC by itself – or perhaps a TEC coupled to a nearby superconductor – may host new kinds of particles,” Folk says. “These would be built out of the ‘normal’ electrons in the TEC, but totally unlike them in many ways: such as their fractional charge, and properties that would make them promising as topological qubits.”

The research is described in Nature.

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If you have worked in a university, research institute or business during the past two decades you will be familiar with the term equality, diversity and inclusion (EDI). There is likely to be an EDI strategy that includes measures and targets to nurture a workforce that looks more like the wider population and a culture in which everyone can thrive. You may find a reasoned business case for EDI, which extends beyond the organization’s legal obligations, to reflect and understand the people that you work with.

Look more closely and it is possible that the “E” in EDI is not actually equality, but rather equity. Equity is increasingly being used as a more active commitment, not least by the Institute of Physics, which publishes Physics World.  How, though, is equity different to equality? What is causing this change of language and will it make any difference in practice?

These questions have become more pressing as discussions around equality and equity have become entwined in the culture wars.  This is a particularly live issue in the US as Donald Trump’s second term as US president has begun to withdraw funding from EDI activities.  But it has also influenced science policy in the UK.

The distinction between equality and equity is often illustrated by a cartoon published in 2016 by the UK artist Angus Maguire (above). It shows a fence and people of variable height gaining an equal view of a baseball match thanks to different numbers of crates that they stand on. This has itself, however, resulted in arguments about other factors such as the conditions necessary to watch the game in the stadium, or indeed even join in. That requires consideration about how the teams and the stadium could adapt to the needs of all potential participants, but also how these changes might affect the experience of others involved.

In terms of education, the Organization for Economic Co-operation and Development (OECD) states that equity “does not mean that all students obtain equal education outcomes, but rather that differences in students’ outcomes are unrelated to their background or to economic and social circumstances over which the students have no control”. This is an admirable goal, but there are questions about how to achieve it.

In OECD member countries, freedom of choice and competition yield social inequalities that flow through to education and careers. This means that governments are continually balancing the benefits of inspiring and rewarding individuals alongside concerns about group injustice.

In 2024, we hosted a multidisciplinary workshop about equity in science, and especially physics. Held at the University of Birmingham, it brought together physicists at different career stages with social scientists and people who had worked on science and education in government, charities and learned societies. At the event, social scientists told us that equality is commonly conceived as a basic right to be treated equally and not discriminated against, regardless of personal characteristics. This right provides a platform for “equality of opportunity” whereby barriers are removed so talent and effort can be rewarded.

In the UK, the promotion of equality of opportunity is enshrined within the country’s Equality Act 2010 and underpins current EDI work in physics. This includes measures to promote physics to young people in deprived areas, and to women and ethnic minorities, as well as mentoring and additional academic and financial support through all stages of education and careers.  It extends to re-shaping the content and promotion of physics courses in universities so they are more appealing and responsive to a wider constituency. In many organizations, there is also training for managers to combat discrimination and bias, whether conscious or not.

Actions like these have helped to improve participation and progression across physics education and careers, but there is still significant underrepresentation and marginalization due to gender, ethnicity and social background. This is not unusual in open and competitive societies where the effects of promoting equal opportunities are often outweighed by the resources and connections of people with characteristics that are highly represented. Talent and effort are crucial in “high-performance” sectors such as academia and industry, but they are not the only factors influencing success.

Physicists at the meeting told us that they are motivated by intellectual curiosity, fascination with the natural world and love for their subject. Yet there is also, in physics, a culture of “genius” and competition, in which confidence is crucial. Facilities and working conditions, which often involve short-term contracts and international mobility, are difficult to balance alongside other life commitments. Although inequalities and exclusions are recognized, they are often ascribed to broader social factors or the inherent requirements of research. As a result, physicists tend not to accept responsibility for inequities within the discipline.

Physics has a culture of “hyper-meritocracy” where being correct counts more than respecting others

Many physicists want merit to be a reflection of talent and effort. But we identified that physics has a culture of “hyper-meritocracy” where being correct counts more than respecting others. Across the community, some believe in positive action beyond the removal of discrimination, but others can be actively hostile to any measure associated with EDI. This is a challenging environment for any young researcher and we heard distressing stories of isolation from women and colleagues who had hidden disabilities or those who were the first in their family to go to university.

The experience, positive or not, when joining a research group as a postgraduate or postdoctoral researcher is often linked with the personality of leaders. Peer groups and networks have helped many physicists through this period of their career, but it is also where the culture in a research group or department can drive some to the margins and ultimately out of the profession. In environments like this, equal opportunities have proved insufficient to advance diversity, let alone inclusion.

Culture change

Organizations that have replaced equality with equity want to signal a commitment not just to equal treatment, but also more equitable outcomes. However, those who have worked in government told us that some people become disengaged, thinking such efforts can only be achieved by reducing standards and threatening cultures they value. Given that physics needs technical proficiency and associated resources and infrastructure, it is not a discipline where equity can mean an equal distribution of positions and resources.

Physics can, though, counter the influence of wider inequalities by helping colleagues who are under-represented to gain the attributes, experiences and connections that are needed to compete successfully for doctoral studentships, research contracts and academic positions. It can also face up to its cultural problems, so colleagues who are minoritized feel less marginalized and they are ultimately recognized for their efforts and contributions.

This will require physicists giving more prominence to marginalized voices as well as critically and honestly examining their culture and tackling unacceptable behaviour. We believe we can achieve this by collaborating with our social science colleagues. That includes gathering and interpreting qualitative data, so there is shared understanding of problems, as well as designing strategies with people who are most affected, so that everyone has a stake in success.

If this happens, we can look forward to a physics community that genuinely practices equity, rather than espousing equality of opportunity.

• This article was based on conference contributions from Saher Ahmed, Clara Barker, Fern Elsdon-Baker, Diane Grayson, Pauline Leonard, Kimberley Scott, David Sweeney and Marika Taylor.

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One hundred and one years ago, Danish physicist Niels Bohr proposed a radical theory together with two young colleagues – Hendrik Kramers and John Slater – in an attempt to resolve some of the most perplexing issues in fundamental physics at the time. Entitled “The Quantum Theory of Radiation”, and published in the Philosophical Magazine, their hypothesis was quickly proved wrong, and has since become a mere footnote in the history of quantum mechanics.

Despite its swift demise, their theory perfectly illustrates the sense of crisis felt by physicists at that moment, and the radical ideas they were prepared to contemplate to resolve it. For in their 1924 paper Bohr and his colleagues argued that the discovery of the “quantum of action” might require the abandonment of nothing less than the first law of thermodynamics: the conservation of energy.

As we celebrate the centenary of Werner Heisenberg’s 1925 quantum breakthrough with the International Year of Quantum Science and Technology (IYQ) 2025, Bohr’s 1924 paper offers a lens through which to look at how the quantum revolution unfolded. Most physicists at that time felt that if anyone was going to rescue the field from the crisis, it would be Bohr. Indeed, this attempt clearly shows signs of the early rift between Bohr and Albert Einstein about the quantum realm, that would turn into a lifelong argument. Remarkably, the paper also drew on an idea that later featured in one of today’s most prominent alternatives to Bohr’s “Copenhagen” interpretation of quantum mechanics.

Genesis of a crisis

The quantum crisis began when German physicist Max Planck proposed the quantization of energy in 1900, as a mathematical trick for calculating the spectrum of radiation from a warm, perfectly absorbing “black body”. Later, in 1905, Einstein suggested taking this idea literally to account for the photoelectric effect, arguing that light consisted of packets or quanta of electromagnetic energy, which we now call photons.

Bohr entered the story in 1912 when, working in the laboratory of Ernest Rutherford in Manchester, he devised a quantum theory of the atom. In Bohr’s picture, the electrons encircling the atomic nucleus (that Rutherford had discovered in 1909) are constrained to specific orbits with quantized energies. The electrons can hop in “quantum jumps” by emitting or absorbing photons with the corresponding energy.

Bohr had no theoretical justification for this ad hoc assumption, but he showed that, by accepting it, he could predict (more or less) the spectrum of the hydrogen atom. For this work Bohr was awarded the 1922 Nobel Prize for Physics, the same year that Einstein collected the prize for his work on light quanta and the photoelectric effect (he had been awarded it in 1921 but was unable to attend the ceremony).

After establishing an institute of theoretical physics (now the Niels Bohr Institute) in Copenhagen in 1917, Bohr’s mission was to find a true theory of the quantum: a mechanics to replace, at the atomic scale, the classical physics of Isaac Newton that worked at larger scales. It was clear that classical physics did not work at the scale of the atom, although Bohr’s correspondence principle asserted that quantum theory should give the same results as classical physics at a large enough scale.

Quantum theory was at the forefront of physics at the time, and so was the most exciting topic for any aspiring young physicist. Three groups stood out as the most desirable places to work for anyone seeking a fundamental mathematical theory to replace the makeshift and sometimes contradictory “old” quantum theory that Bohr had cobbled together: that of Arnold Sommerfeld in Münich, of Max Born in Göttingen, and of Bohr in Copenhagen.

Dutch physicist Hendrik Kramers had hoped to work on his doctorate with Born – but in 1916 the First World War ruled that out, and so he opted instead for Copenhagen, in politically neutral Denmark. There he became Bohr’s assistant for ten years: as was the case with several of Bohr’s students, Kramers did the maths (it was never Bohr’s forte) while Bohr supplied the ideas, philosophy and kudos. Kramers ended up working on an impressive range of problems, from chemical physics to pure mathematics.

Reckless and radical

One of the most vexing question for Bohr and his Copenhagen circle in the early 1920s was how to think about electron orbits in atoms. Try as they might, they couldn’t find a way to make the orbits “fit” with experimental observations of atomic spectra.

Perhaps, in quantum systems like atoms, we have to abandon any attempt to construct a physical picture at all

Bohr and others, including Heisenberg, began to voice a possibility that seemed almost reckless: perhaps, in quantum systems like atoms, we have to abandon any attempt to construct a physical picture at all. Maybe we just can’t think of quantum particles as objects moving along trajectories in space and time.

This struck others, such as Einstein, as desperate, if not crazy. Surely the goal of science had always been to offer a picture of the world in terms of “things happening to objects in space”. What else could there be than that? How could we just give it all up?

But it was worse than that. For one thing, Bohr’s quantum jumps were supposed to happen instantaneously: an electron, say, jumping from one orbit to another in no time at all. In classical physics, everything happens continuously: a particle gets from here to there by moving smoothly across the intervening space, in some finite time. The discontinuities of quantum jumps seemed to some – like Austrian physicist Erwin Schrödinger in Vienna – bordering on the obscene.

Worse still was the fact that while the old quantum theory stipulated the energy of quantum jumps, there was nothing to dictate when they would happen – they simply did. In other words, there was no causal kick that instigated a quantum jump: the electron just seemed to make up its own mind about when to jump. As Heisenberg would later proclaim in his 1927 paper on the uncertainty principle (Zeitschrift für Physik 43 172),  quantum theory “establishes the final failure of causality”.

Such notions were not the only source of friction between the Copenhagen team and Einstein. Bohr didn’t like light quanta. While they seemed to explain the photoelectric effect, Bohr was convinced that light had to be fundamentally wave-like, so that photons (to use the anachronistic term) were only a way of speaking, not real entities.

To add to the turmoil in 1924, the French physicist Louis de Broglie had, in his doctoral thesis for the Sorbonne, turned the quantum idea on its head by proposing that particles such as electrons might show wave-like behaviour. Einstein had at first considered this too wild, but soon came round to the idea.

Go where the waves take you

In 1924 these virtually heretical ideas were only beginning to surface, but they were creating such a sense of crisis that it seemed anything was possible. In the 1960s, science historian Paul Forman suggested that the feverish atmosphere in physics was part of an even wider cultural current. By rejecting causality and materialism, the German quantum physicists, Forman said, were attempting to align their ideas with a rejection of mechanistic thinking while embracing the irrational – as was the fashion in the philosophical and intellectual circles of the beleaguered Weimar republic. The idea has been hotly debated by historians and philosophers of science – but it was surely in Copenhagen, not Munich or Göttingen, that the most radical attitudes to quantum theory were developing.

Then, just before Christmas in 1923, a new student arrived at Copenhagen. John Clarke Slater, who had a PhD in physics from Harvard, turned up at Bohr’s institute with a bold idea. “You know those difficulties about not knowing whether light is old-fashioned waves or Mr Einstein’s light particles”, he wrote to his family during a spell in Cambridge that November. “I had a really hopeful idea… I have both the waves and the particles, and the particles are sort of carried along by the waves, so that the particles go where the waves take them.” The waves were manifested in a kind of “virtual field” of some kind that spread throughout the system, and they acted to “pilot” the particles.

Bohr was mostly not a fan of Slater’s idea, not least because it retained the light particles that he wished to dispose of. But he liked Slater’s notion of a virtual field that could put one part of a quantum system in touch with others. Together with Slater and Kramers, Bohr prepared a paper in a remarkably short time (especially for him) outlining what became known as the Bohr-Kramers-Slater (BKS) theory. They sent it off to the Philosophical Magazine (where Bohr had published his seminal papers on the quantum atom) at the end of January 1924, and it was published in May (47(281) 785). As was increasingly characteristic of Bohr’s style, it was free of any mathematics (beyond Einstein’s quantum relationship E=hν).

In the BKS picture, an excited atom about to emit light can “communicate continually” with the other atoms around it via the virtual field. The transition, with emission of a light quantum, is then not spontaneous but induced by the virtual field. This mechanism could solve the long-standing question of how an atom “knows” which frequency of light to emit in order to reach another energy level: the virtual field effectively puts the atom “in touch” with all the possible energy states of the system.

The problem was that this meant the emitting atom was in instant communication with its environment all around – which violated the law of causality. Well then, so much the worse for causality: BKS abandoned it. The trio’s theory also violated the conservation of energy and momentum – so they had to go too.

Causality and conservation, abandoned

But wait: hadn’t these conservation laws been proved? In 1923 the American physicist Arthur Compton in Cambridge had shown that when light is scattered by electrons, they exchange energy, and the frequency of the light decreases as it gives up energy to the electrons. The results of Compton’s experiments agreed perfectly with predictions made on the assumptions that light is a stream of quanta (photons) and that their collisions with electrons conserve energy and momentum.

Ah, said BKS, but that’s only true statistically. The quantities are conserved on average, but not in individual collisions. After all, such statistical outcomes were familiar to physicists: that was the basis of the second law of thermodynamics, which presented the inexorable increase in entropy as a statistical phenomenon that need not constrain processes involving single particles.

The radicalism of the BKS paper got a mixed reception. Einstein, perhaps predictably, was dismissive. “Abandonment of causality as a matter of principle should be permitted only in the most extreme emergency”, he wrote. Wolfgang Pauli, who had worked in Copenhagen in 1922–23, confessed to being “completely negative” about the idea. Born and Schrödinger were more favourable.

But the ultimate arbiter is experiment. Was energy conservation really violated in single-particle interactions? The BKS paper motivated others to find out. In early 1925, German physicists Walther Bothe and Hans Geiger in Berlin looked more closely at Compton’s X-ray scattering by electrons. Having read the BKS paper, Bothe felt that “it was immediately obvious that this question would have to be decided experimentally, before definite progress could be made.”

Geiger agreed, and the duo devised a scheme for detecting both the scattered electron and the scattered photon in separate detectors. If causality and energy conservation were preserved, the detections should be simultaneous; while any delay between them could indicate a violation. As Bothe would later recall “The ‘question to Nature’ which the experiment was designed to answer could therefore be formulated as follows: is it exactly a scatter quantum and a recoil electron that are simultaneously emitted in the elementary process, or is there merely a statistical relationship between the two?” It was incredibly painstaking work to seek such coincident detections using the resources then available. But in April 1925 Geiger and Bothe reported simultaneity within a millisecond – close enough to make a strong case that Compton’s treatment, which assumed energy conservation, was correct. Compton himself, working with Alfred Simon using a cloud chamber, confirmed that energy and momentum were conserved for individual events (Phys. Rev. 26 289).

Revolutionary defeat… singularly important

Bothe was awarded the 1954 Nobel Prize for Physics for the work. He shared it with Born for his work on quantum theory, and Geiger would surely have been a third recipient, if he had not died in 1945. In his Nobel speech, Bothe definitively stated that “the strict validity of the law of the conservation of energy even in the elementary process had been demonstrated, and the ingenious way out of the wave-particle problem discussed by Bohr, Kramers, and Slater was shown to be a blind alley.”

Bohr was gracious in his defeat, writing to a colleague in April 1925 that “It seems… there is nothing else to do than to give our revolutionary efforts as honourable a funeral as possible.” Yet he was soon to have no need of that particular revolution, for just a few months later Heisenberg, who had returned to Göttingen after working with Bohr in Copenhagen for six months, came up the first proper theory of quantum mechanics, later called matrix mechanics.

“In spite of its short lifetime, the BKS theory was singularly important,” says historian of science Helge Kragh, now emeritus professor at the Niels Bohr Institute. “Its radically new approach paved the way for a greater understanding, that methods and concepts of classical physics could not be carried over in a future quantum mechanics.”

The Bothe-Geiger experiment that [the paper] inspired was not just an important milestone in early particle physics. It was also a crucial factor in Heisenberg’s argument [about] the probabilistic character of his matrix mechanics

The BKS paper was thus in a sense merely a mistaken curtain-raiser for the main event. But the Bothe-Geiger experiment that it inspired was not just an important milestone in early particle physics. It was also a crucial factor in Heisenberg’s argument that the probabilistic character of his matrix mechanics (and also of Schrödinger’s 1926 version of quantum mechanics, called wave mechanics) couldn’t be explained away as a statistical expression of our ignorance about the details, as it is in classical statistical mechanics.

Rather, the probabilities that emerged from Heisenberg’s and Schrödinger’s theories applied to individual events: they were, Heisenberg said, fundamental to the way single particles behave. Schrödinger was never happy with that idea, but today it seems inescapable.

Over the next few years, Bohr and Heisenberg argued that the new quantum mechanics indeed smashed causality and shattered the conventional picture of reality as an objective world of objects moving in space–time with fixed properties. Assisted by Born, Wolfgang Pauli and others, they articulated the “Copenhagen interpretation”, which became the predominant vision of the quantum world for the rest of the century.

Failed connections

Slater wasn’t at all pleased with what became of the idea he took to Copenhagen. Bohr and Kramers had pressured him into accepting their take on it, “without the little lump carried along on the waves”, as he put it in mid-January. “I am willing to let them have their way”, he wrote at the time, but in retrospect he felt very unhappy about his time in Denmark. After the BKS theory was disproved, Bohr wrote to Slater saying “I have a bad conscience in persuading you to our views”.

Slater replied that there was no need for that. But in later life – after he had made a name for himself in solid-state physics – Slater admitted to a great deal of resentment. “I completely failed to make any connection with Bohr”, he said in a 1963 interview with the historian of science Thomas Kuhn. “I fought with them [Bohr and Kramers] so seriously that I’ve never had any respect for those people since. I had a horrible time in Copenhagen.” While most of Bohr’s colleagues and students expressed adulation, Slater’s was a rare dissenting voice.

But Slater might have reasonably felt more aggrieved at what became of his “pilot-wave” idea. Today, that interpretation of quantum theory is generally attributed to de Broglie – who intimated a similar notion in his 1924 thesis, before presenting the theory in more detail at the famous 1927 Solvay Conference – and to American physicist David Bohm, who revitalized the idea in the 1950s. Initially dismissed on both occasions, the de Broglie-Bohm theory has gained advocates in recent years, not least because it can be applied to a classical hydrodynamic analogue, in which oil droplets are steered by waves on an oil surface.

Whether or not it is the right way to think about quantum mechanics, the pilot-wave theory touches on the deep philosophical problems of the field. Can we rescue an objective reality of concrete particles with properties described by hidden variables, as Einstein had advocated, from the fuzzy veil that Bohr and Heisenberg seemed to draw over the quantum world? Perhaps Slater would at least be gratified to know that Bohr has not yet had the last word.

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In a ground-breaking theoretical study, two physicists have identified a new class of quasiparticle called the paraparticle. Their calculations suggest that paraparticles exhibit quantum properties that are fundamentally different from those of familiar bosons and fermions, such as photons and electrons respectively.

Using advanced mathematical techniques, Kaden Hazzard at Rice University in the US and his former graduate student Zhiyuan Wang, now at the Max Planck Institute of Quantum Optics in Germany, have meticulously analysed the mathematical properties of paraparticles and proposed a real physical system that could exhibit paraparticle behaviour.

“Our main finding is that it is possible for particles to have exchange statistics different from those of fermions or bosons, while still satisfying the important physical principles of locality and causality,” Hazzard explains.

Particle exchange

In quantum mechanics, the behaviour of particles (and quasiparticles) is probabilistic in nature and is described by mathematical entities known as wavefunctions. These govern the likelihood of finding a particle in a particular state, as defined by properties like position, velocity, and spin. The exchange statistics of a specific type of particle dictates how its wavefunction behaves when two identical particles swap places.

For bosons such as photons, the wavefunction remains unchanged when particles are exchanged. This means that many bosons can occupy the same quantum state, enabling phenomena like lasers and superfluidity. In contrast, when fermions such as electrons are exchanged, the sign of the wavefunction flips from positive to negative or vice versa. This antisymmetric property prevents fermions from occupying the same quantum state. This underpins the Pauli exclusion principle and results in the electronic structure of atoms and the nature of the periodic table.

Until now, physicists believed that these two types of particle statistics – bosonic and fermionic – were the only possibilities in 3D space. This is the result of fundamental principles like locality, which states that events occurring at one point in space cannot instantaneously influence events at a distant location.

Breaking boundaries

Hazzard and Wang’s research overturns the notion that 3D systems are limited to bosons and fermions and shows that new types of particle statistics, called parastatistics, can exist without violating locality.

The key insight in their theory lies in the concept of hidden internal characteristics. Beyond the familiar properties like position and spin, paraparticles require additional internal parameters that enable more complex wavefunction behaviour. This hidden information allows paraparticles to exhibit exchange statistics that go beyond the binary distinction of bosons and fermions.

Paraparticles exhibit phenomena that resemble – but are distinct from – fermionic and bosonic behaviours. For example, while fermions cannot occupy the same quantum state, up to two paraparticles could be allowed to coexist in the same point in space. This behaviour strikes a balance between the exclusivity of fermions and the clustering tendency of bosons.

Bringing paraparticles to life

While no elementary particles are known to exhibit paraparticle behaviour, the researchers believe that paraparticles might manifest as quasiparticles in engineered quantum systems or certain materials. A quasiparticle is particle-like collective excitation of a system. A familiar example is the hole, which is created in a semiconductor when a valence-band electron is excited to the conduction band. The vacancy (or hole) left in the valence band behaves as a positively-charged particle that can travel through the semiconductor lattice.

Experimental systems of ultracold atoms created by collaborators of the duo could be one place to look for the exotic particles. “We are working with them to see if we can detect paraparticles there,” explains Wang.

In ultracold atom experiments, lasers and magnetic fields are used to trap and manipulate atoms at temperatures near absolute zero. Under these conditions, atoms can mimic the behaviour of more exotic particles. The team hopes that similar setups could be used to observe paraparticle-like behaviour in higher-dimensional systems, such as 3D space. However, further theoretical advances are needed before such experiments can be designed.

Far-reaching implications

The discovery of paraparticles could have far-reaching implications for physics and technology. Fermionic and bosonic statistics have already shaped our understanding of phenomena ranging from the stability of neutron stars to the behaviour of superconductors. Paraparticles could similarly unlock new insights into the quantum world.

“Fermionic statistics underlie why some systems are metals and others are insulators, as well as the structure of the periodic table,” Hazzard explains. “Bose-Einstein condensation [of bosons] is responsible for phenomena such as superfluidity. We can expect a similar variety of phenomena from paraparticles, and it will be exciting to see what these are.”

As research into paraparticles continues, it could open the door to new quantum technologies, novel materials, and deeper insights into the fundamental workings of the universe. This theoretical breakthrough marks a bold step forward, pushing the boundaries of what we thought possible in quantum mechanics.

The paraparticles are described in Nature.

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If you’re a postdoc who wants to nail down that permanent faculty position, it’s wise to publish a highly cited paper after your PhD. That’s the conclusion of a study by an international team of researchers, which finds that publication rates and performance during the postdoc period is key to academic retention and early-career success. Their analysis also reveals that more than four in 10 postdocs drop out of academia.

A postdoc is usually a temporary appointment that is seen as preparation for an academic career. Many researchers, however, end up doing several postdocs in a row as they hunt for a permanent faculty job. “There are many more postdocs than there are faculty positions, so it is a kind of systemic bottleneck,” says Petter Holme, a computer scientist at Aalto University in Finland, who led the study.

Previous research into academic career success has tended to overlook the role of a postdoc, focusing instead on, say, the impact of where researchers did their PhD. To eke out the effect of a postdoc, Holme and colleagues combined information of academics’ career stages from LinkedIn with their publication history obtained from Microsoft Academic Graph. The resulting global dataset covered 45, 572 careers spanning 25 years across all academic disciplines.

Overall, they found, 41% of postdocs left academia. But researchers who publish a highly cited paper as a postdoc are much more likely to pursue a faculty career – whether they published a highly cited paper during their PhD degree, or not. Publication rate is also vital, with researchers who publish less as postdocs compared to their PhD days being more likely to drop out of academia. Conversely, as productivity increased, so did the likelihood of a postdoc gaining a faculty position.

Expanding horizons

Holme says their results suggest that a researcher only has a few years “to get on the positive feedback loop, where one success leads to another”. In fact, the team found that a “moderate” change in research topic when moving from PhD to postdoc could improve future success. “It is a good thing to change your research focus, but not too much,” says Holme because it widens perspective without having to learn an entire new research topic from scratch.

Likewise, shifting perspective by moving abroad can also benefit postdocs. The analysis shows that a researcher moving abroad for a postdoc boosts their citations, but a move to a different institution in the same country has a negligible impact.

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