Rapid technical innovation in quantum computing has yielded an array of hardware platforms that can run increasingly sophisticated algorithms. In the real world, however, such technical advances will remain little more than a curiosity if they are not adopted by businesses and the public sector to drive positive change. As a result, one key priority for the UK’s National Quantum Computing Centre (NQCC) has been to help companies and other organizations to gain an early understanding of the value that quantum computing can offer for improving performance and enhancing outcomes.

To meet that objective the NQCC has supported several feasibility studies that enable commercial organizations in the UK to work alongside quantum specialists to investigate specific use cases where quantum computing could have a significant impact within their industry. One prime example is a project involving the high-street bank HSBC, which has been exploring the potential of quantum technologies for spotting the signs of fraud in financial transactions. Such fraudulent activity, which affects millions of people every year, now accounts for about 40% of all criminal offences in the UK and in 2023 generated total losses of more than £2.3 bn across all sectors of the economy.

Banks like HSBC currently exploit classical machine learning to detect fraudulent transactions, but these techniques require a large computational overhead to train the models and deliver accurate results. Quantum specialists at the bank have therefore been working with the NQCC, along with hardware provider Rigetti and the Quantum Software Lab at the University of Edinburgh, to investigate the capabilities of quantum machine learning (QML) for identifying the tell-tale indicators of fraud.

“HSBC’s involvement in this project has brought transactional fraud detection into the realm of cutting-edge technology, demonstrating our commitment to pushing the boundaries of quantum-inspired solutions for near-term benefit,” comments Philip Intallura, Group Head of Quantum Technologies at HSBC. “Our philosophy is to innovate today while preparing for the quantum advantage of tomorrow.”

Another study focused on a key problem in the aviation industry that has a direct impact on fuel consumption and the amount of carbon emissions produced during a flight. In this logistical challenge, the aim was to find the optimal way to load cargo containers onto a commercial aircraft. One motivation was to maximize the amount of cargo that can be carried, the other was to balance the weight of the cargo to reduce drag and improve fuel efficiency.

“Even a small shift in the centre of gravity can have a big effect,” explains Salvatore Sinno of technology solutions company Unisys, who worked on the project along with applications engineers at the NQCC and mathematicians at the University of Newcastle. “On a Boeing 747 a displacement of just 75 cm can increase the carbon emissions on a flight of 10,000 miles by four tonnes, and also increases the fuel costs for the airline company.”

With such a large number of possible loading combinations, classical computers cannot produce an exact solution for the optimal arrangement of cargo containers. In their project the team improved the precision of the solution by combining quantum annealing with high-performance computing, a hybrid approach that Unisys believes can offer immediate value for complex optimization problems. “We have reached the limit of what we can achieve with classical computing, and with this work we have shown the benefit of incorporating an element of quantum processing into our solution,” explains Sinno.

The HSBC project team also found that a hybrid quantum–classical solution could provide an immediate performance boost for detecting anomalous transactions. In this case, a quantum simulator running on a classical computer was used to run quantum algorithms for machine learning. “These simulators allow us to execute simple QML programmes, even though they can’t be run to the same level of complexity as we could achieve with a physical quantum processor,” explains Marco Paini, the project lead for Rigetti. “These simulations show the potential of these low-depth QML programmes for fraud detection in the near term.”

The team also simulated more complex QML approaches using a similar but smaller-scale problem, demonstrating a further improvement in performance. This outcome suggests that running deeper QML algorithms on a physical quantum processor could deliver an advantage for detecting anomalies in larger datasets, even though the hardware does not yet provide the performance needed to achieve reliable results. “This initiative not only showcases the near-term applicability of advanced fraud models, but it also equips us with the expertise to leverage QML methods as quantum computing scales,” comments Intellura.

Indeed, the results obtained so far have enabled the project partners to develop a roadmap that will guide their ongoing development work as the hardware matures. One key insight, for example, is that even a fault-tolerant quantum computer would struggle to process the huge financial datasets produced by a bank like HSBC, since a finite amount of time is needed to run the quantum calculation for each data point. “From the simulations we found that the hybrid quantum–classical solution produces more false positives than classical methods,” says Paini. “One approach we can explore would be to use the simulations to flag suspicious transactions and then run the deeper algorithms on a quantum processor to analyse the filtered results.”

This particular project also highlighted the need for agreed protocols to navigate the strict rules on data security within the banking sector. For this project the HSBC team was able to run the QML simulations on its existing computing infrastructure, avoiding the need to share sensitive financial data with external partners. In the longer term, however, banks will need reassurance that their customer information can be protected when processed using a quantum computer. Anticipating this need, the NQCC has already started to work with regulators such as the Financial Conduct Authority, which is exploring some of the key considerations around privacy and data security, with that initial work feeding into international initiatives that are starting to consider the regulatory frameworks for using quantum computing within the financial sector.

For the cargo-loading project, meanwhile, Sinno says that an important learning point has been the need to formulate the problem in a way that can be tackled by the current generation of quantum computers. In practical terms that means defining constraints that reduce the complexity of the problem, but that still reflect the requirements of the real-world scenario. “Working with the applications engineers at the NQCC has helped us to understand what is possible with today’s quantum hardware, and how to make the quantum algorithms more viable for our particular problem,” he says. “Participating in these studies is a great way to learn and has allowed us to start using these emerging quantum technologies without taking a huge risk.”

Indeed, one key feature of these feasibility studies is the opportunity they offer for different project partners to learn from each other. Each project includes an end-user organization with a deep knowledge of the problem, quantum specialists who understand the capabilities and limitations of present-day solutions, and academic experts who offer an insight into emerging theoretical approaches as well as methodologies for benchmarking the results. The domain knowledge provided by the end users is particularly important, says Paini, to guide ongoing development work within the quantum sector. “If we only focused on the hardware for the next few years, we might come up with a better technical solution but it might not address the right problem,” he says. “We need to know where quantum computing will be useful, and to find that convergence we need to develop the applications alongside the algorithms and the hardware.”

Another major outcome from these projects has been the ability to make new connections and identify opportunities for future collaborations. As a national facility NQCC has played an important role in providing networking opportunities that bring diverse stakeholders together, creating a community of end users and technology providers, and supporting project partners with an expert and independent view of emerging quantum technologies. The NQCC has also helped the project teams to share their results more widely, generating positive feedback from the wider community that has already sparked new ideas and interactions.

“We have been able to network with start-up companies and larger enterprise firms, and with the NQCC we are already working with them to develop some proof-of-concept projects,” says Sinno. “Having access to that wider network will be really important as we continue to develop our expertise and capability in quantum computing.”

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Through new experiments, researchers in Switzerland have tested models of how microwaves affect low-temperature chemical reactions between ions and atoms. Through their innovative setup, Valentina Zhelyazkova and colleagues at ETH Zurich showed for the first time how the application of microwave pulses can slow down reaction rates via nonthermal mechanisms.

Physicists have been studying chemical reactions between ions and neutral molecules for some time. At close to room temperature, classical models can closely predict how the electric fields emanating from ions will induce dipoles in nearby neutral molecules, allowing researchers to calculate these reaction rates with impressive accuracy. Yet as temperatures drop close to absolute zero, a wide array of more complex effects come into play, which have gradually been incorporated into the latest theoretical models.

“At low temperatures, models of reactivity must include the effects of the permanent electric dipoles and quadrupole moments of the molecules, the effect of their vibrational and rotational motion,” Zhelyazkova explains. “At extremely low temperatures, even the quantum-mechanical wave nature of the reactants must be considered.”

Rigorous experiments

Although these low-temperature models have steadily improved in recent years, the ability to put them to the test through rigorous experiments has so far been hampered by external factors.

In particular, stray electric fields in the surrounding environment can heat the ions and molecules, so that any important quantum effects are quickly drowned out by noise. “Consequently, it is only in the past few years that experiments have provided information on the rates of ion–molecule reactions at very low temperatures,” Zhelyazkova explains.

In their study, Zhelyazkova’s team improved on these past experiments through an innovative approach to cooling the internal motions of the molecules being heated by stray electric fields. Their experiment involved a reaction between positively-charged helium ions and neutral molecules of carbon monoxide (CO). This creates neutral atoms of helium and oxygen, and a positively-charged carbon atom.

To initiate the reaction, the researchers created separate but parallel supersonic beams of helium and CO that were combined in a reaction cell. “In order to overcome the problem of heating the ions by stray electric fields, we study the reactions within the distant orbit of a highly excited electron, which makes the overall system electrically neutral without affecting the ion–molecule reaction taking place within the electron orbit,” explains ETH’s Frédéric Merkt.

Giant atoms

In such a “Rydberg atom”, the highly excited electron is some distance from the helium nucleus and its other electron. As a result, a Rydberg helium atom can be considered an ion with a “spectator” electron, which has little influence over how the reaction unfolds. To ensure the best possible accuracy, “we use a printed circuit board device with carefully designed surface electrodes to deflect one of the two beams,” explains ETH’s, Fernanda Martins. “We then merged this beam with the other, and controlled the relative velocity of the two beams.”

Altogether, this approach enabled the researchers to cool the molecules internally to temperatures below 10 K – where their quantum effects can dominate over externally induced noise. With this setup, Zhelyazkova, Merkt, Martins, and their colleagues could finally put the latest theoretical models to the test.

According to the latest low-temperature models, the rate of the CO–helium ion reaction should be determined by the quantized rotational states of the CO molecule – whose energies lie within the microwave range. In this case, the team used microwave pulses to put the CO into different rotational states, allowing them to directly probe their influence on the overall reaction rate.

Three important findings

Altogether, their experiment yielded three important findings. It confirmed that the reaction rate can vary, depending on the rotational state of the CO molecule; it showed that this reactivity can be modified by using a short microwave pulse to excite the CO molecule from its ground state to its first excited state – with the first excited state being less reactive than the ground state.

The third and most counterintuitive finding is that microwaves can slow down the reaction rate, via mechanisms unrelated to the heat they impart on the molecules absorbing them. “In most applications of microwaves in chemical synthesis, the microwaves are used as a way to thermally heat the molecules up, which always makes them more reactive,” Zhelyazkova says.

Building on the success of their experimental approach, the team now hopes to investigate these nonthermal mechanisms in more detail – with the aim to shed new light on how microwaves can influence chemical reactions via effects other than heating. In turn, their results could ultimately pave the way for advanced new techniques for fine-tuning the rate of reactions between ions and neutral molecules.

The research is described in Physical Review Letters.

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A quarter of a century ago, in May 2000, I published an article entitled “Why science thrives on criticism”. The article, which ran to slightly over a page in Physics World magazine, was the first in a series of columns called Critical Point. Periodicals, I said, have art and music critics as well as sports and political commentators, and book and theatre reviewers too. So why shouldn’t Physics World have a science critic?

The implication that I had a clear idea of the “critical point” for this series was not entirely accurate. As the years go by, I have found myself improvising, inspired by politics, books, scientific discoveries, readers’ thoughts, editors’ suggestions and more. If there is one common theme, it’s that science is like a workshop – or a series of loosely related workshops – as I argued in The Workshop and the World, a book that sprang from my columns.

Workshops are controlled environments, inside which researchers can stage and study special things – elementary particles, chemical reactions, plant uptakes of nutrients – that appear rarely or in a form difficult to study in the surrounding world. Science critics do not participate in the workshops themselves or even judge their activities. What they do is evaluate how workshops and worlds interact.

This can happen in three ways

Critical triangle

First is to explain why what’s going on inside the workshops matters to outsiders. Sometimes, those activities can be relatively simple to describe, which leads to columns concerning all manner of everyday activities. I have written, for example, about the physics of coffee and breadmaking. I’ve also covered toys, tops, kaleidoscopes, glass and other things that all of us – physicists and non-physicists alike – use, value and enjoy.

Sometimes I draw out more general points about why those activities are important. Early on, I invited readers to nominate their most beautiful experiments in physics. (Spoiler alert: the clear winner was the double-slit experiment with electrons.) I later did something similar about the cultural impact of equations – inviting readers to pick their favourites and reporting on their results (second spoiler alert: Maxwell’s equations came top). I also covered readers’ most-loved literature about laboratories.

Physicists often engage in activities that might seem inconsequential to them yet are an intrinsic part of the practice of physics

When viewing science as workshops, a second role is to explain why what’s outside the workshops matters to insiders. That’s because physicists often engage in activities that might seem inconsequential to them – they’re “just what the rest the world does” – yet are an intrinsic part of the practice of physics. I’ve covered, for example, physicists taking out patents, creating logos, designing lab architecture, taking holidays, organizing dedications, going on retirement and writing memorials for the deceased.

Such activities I term “black elephants”. That’s because they’re a cross between things physicists don’t want to talk about (“elephants in the room”) and things that force them to renounce cherished notions (just as “black swans” disprove that “all swans are white”).

A third role of a science critic is to explain what matters that takes place both inside and outside the workshop. I’m thinking of things like competition, leadership, trust,  surprise, workplace training courses, cancel culture and even jokes and funny tales. Interpretations of the meaning of quantum mechanics, such as “QBism”, which I covered both in 2019 and 2022, are an ongoing interest. That’s because they’re relevant both to the structure of physics and to philosophy as they disrupt notions of realism, objectivity, temporality and the scientific method.

Being critical

The term “critic” may suggest someone with a congenitally negative outlook, but that’s wrong. My friend Fred Cohn, a respected opera critic, told me that, in a conversation after a concert, he criticized the performance of the singer Luciano Pavarotti. His remark provoked a woman to shout angrily at him: “Could you do better?” Of course not! It’s the critic’s role to evaluate performances of an activity, not to perform the activity oneself.

Having said that, sometimes a critic must be critical to be honest. In particular, I hate it when scientists try to delegitimize the experience of non-scientists by saying, for example, that “time does not exist”. Or when they pretend they don’t see rainbows but wavelengths of light or that they don’t see sunrises or the plane of a Foucault pendulum move but the Earth spinning. Comments like that turn non-scientists off science by making it seem elitist and other-worldly. It’s what I call “scientific gaslighting”.

Most of all, I hate it when scientists pontificate that philosophy is foolish or worthless, especially when it’s the likes of Steven Pinker, who ought to know better. Writing in Nature (518 300), I once criticized the great theoretical physicist Steven Weinberg, who I counted as a friend, for taking a complex and multivalent text, plucking out a single line, and misreading it as if the line were from a physics text.

The text in question was Plato’s Phaedo, where Socrates expresses his disappointment with his fellow philosopher Anaxagoras for giving descriptions of heavenly bodies “in purely physical terms, without regard to what is best”. Weinberg claimed this statement meant that Socrates “was not very interested in natural science”. Nothing could be further from the truth.

At that moment in the Phaedo, Socrates is recounting his intellectual autobiography. He has just come to the point where, as a youth, he was entranced by materialism and was eager to hear Anaxagoras’s opposing position. When Anaxagoras promised to describe the heavens both mechanically and as the product of a wise and divine mind but could do only the former, Socrates says he was disappointed.

Weinberg’s jibe ignores the context. Socrates is describing how he had once embraced Anaxagoras’s view of a universe ruled by a divine mind but later rejected that view. As an adult, Socrates learned to test hypotheses and other claims through putting them to the test, just as modern-day scientists do. Weinberg was misrepresenting Socrates by describing a position that he later abandoned.

The critical point of the critical point

Ultimately, the “critical point” of my columns over the last 25 years has been to provoke curiosity and excitement about what philosophers, historians and sociologists do for science. I’ve also wanted to raise awareness that these fields are not just fripperies but essential if we are to fully understand and protect scientific activity.

As I have explained several times – especially in the wake of the US shutting its High Flux Beam Reactor and National Tritium Labeling Facility – scientists need to understand and relate to the surrounding world with the insight of humanities scholars. Because if they don’t, they are in danger of losing their workshops altogether.

• Explore the best of Robert P Crease’s Critical Point articles in this special collection.

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New measurements by physicists from the University of Surrey in the UK have shed fresh light on where the universe’s heavy elements come from. The measurements, which were made by smashing high-energy protons into a uranium target to generate strontium ions, then accelerating these ions towards a second, helium-filled target, might also help improve nuclear reactors.

The origin of the elements that follow iron in the periodic table is one of the biggest mysteries in nuclear astrophysics. As Surrey’s Matthew Williams explains, the standard picture is that these elements were formed when other elements captured neutrons, then underwent beta decay. The two ways this can happen are known as the rapid (r) and slow (s) processes.

The s-process occurs in the cores of stars and is relatively well understood. The r-process is comparatively mysterious. It occurs during violent astrophysical events such as certain types of supernovae and neutron star mergers that create an abundance of free neutrons. In these neutron-rich environments, atomic nuclei essentially capture neutrons before the neutrons can turn into protons via beta-minus decay, which occurs when a neutron emits an electron and an antineutrino.

From the night sky to the laboratory

One way of studying the r-process is to observe older stars. “Studies on heavy element abundance patterns in extremely old stars provide important clues here because these stars formed at times too early for the s-process to have made a significant contribution,” Williams explains. “This means that the heavy element pattern in these old stars may have been preserved from material ejected by prior extreme supernovae or neutron star merger events, in which the r-process is thought to happen.”

Recent observations of this type have revealed that the r-process is not necessarily a single scenario with a single abundance pattern. It may also have a “weak” component that is responsible for making elements with atomic numbers ranging from 37 (rubidium) to 47 (silver), without getting all the way up to the heaviest elements such as gold (atomic number 79) or actinides like thorium (90) and uranium (92).

This weak r-process could occur in a variety of situations, Williams explains. One scenario involves radioactive isotopes (that is, those with a few more neutrons than their stable counterparts) forming in hot neutrino-driven winds streaming from supernovae. This “flow” of nucleosynthesis towards higher neutron numbers is caused by processes known as (alpha,n) reactions, which occur when a radioactive isotope fuses with a helium nucleus and spits out a neutron. “These reactions impact the final abundance pattern before the neutron flux dissipates and the radioactive nuclei decay back to stability,” Williams says. “So, to match predicted patterns to what is observed, we need to know how fast the (alpha,n) reactions are on radioactive isotopes a few neutrons away from stability.”

The ⁹⁴Sr(alpha,n)⁹⁷Zr reaction

To obtain this information, Williams and colleagues studied a reaction in which radioactive strontium-94 absorbs an alpha particle (a helium nucleus), then emits a neutron and transforms into zirconium-97. To produce the radioactive ⁹⁴Sr beam, they fired high-energy protons at a uranium target at TRIUMF, the Canadian national accelerator centre. Using lasers, they selectively ionized and extracted strontium from the resulting debris before filtering out ⁹⁴Sr ions with a magnetic spectrometer.

The team then accelerated a beam of these ⁹⁴Sr ions to energies representative of collisions that would happen when a massive star explodes as a supernova. Finally, they directed the beam onto a nanomaterial target made of a silicon thin film containing billions of small nanobubbles of helium. This target was made by researchers at the Materials Science Institute of Seville (CSIC) in Spain.

“This thin film crams far more helium into a small target foil than previous techniques allowed, thereby enabling the measurement of helium burning reactions with radioactive beams that characterize the weak r-process,” Williams explains.

To identify the ⁹⁴Sr(alpha,n)⁹⁷Zr reactions, the researchers used a mass spectrometer to select for ⁹⁷Zr while simultaneously using an array of gamma-ray detectors around the target to look for the gamma rays it emits. When they saw both a heavy ion with an atomic mass of 97 and a ⁹⁷Zr gamma ray, they knew they had identified the reaction of interest. In doing so, Williams says, they were able to measure the probability that this reaction occurs at the energies and temperatures present in supernovae.

Williams thinks that scientists should be able to measure many more weak r-process reactions using this technology. This should help them constrain where the weak r-process comes from. “Does it happen in supernovae winds? Or can it happen in a component of ejected material from neutron star mergers?” he asks.

As well as shedding light on the origins of heavy elements, the team’s findings might also help us better understand how materials respond to the high radiation environments in nuclear reactors. “By updating models of how readily nuclei react, especially radioactive nuclei, we can design components for these reactors that will operate and last longer before needing to be replaced,” Williams says.

The work is detailed in Physical Review Letters.

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Superpositions of quantum states known as Schrödinger cat states can be created in “hot” environments with temperatures up to 1.8 K, say researchers in Austria and Spain. By reducing the restrictions involved in obtaining ultracold temperatures, the work could benefit fields such as quantum computing and quantum sensing.

In 1935, Erwin Schrödinger used a thought experiment now known as “Schrödinger’s cat” to emphasize what he saw as a problem with some interpretations of quantum theory. His gedankenexperiment involved placing a quantum system (a cat in a box with a radioactive sample and a flask of poison) in a state that is a superposition of two states (“alive cat” if the sample has not decayed and “dead cat” if it has). These superposition states are now known as Schrödinger cat states (or simply cat states) and are useful in many fields, including quantum computing, quantum networks and quantum sensing.

Creating a cat state, however, requires quantum particles to be in their ground state. This, in turn, means cooling them to extremely low temperatures. Even marginally higher temperatures were thought to destroy the fragile nature of these states, rendering them useless for applications. But the need for ultracold temperatures comes with its own challenges, as it restricts the range of possible applications and hinders the development of large-scale systems such as powerful quantum computers.

Cat on a hot tin…microwave cavity?

The new work, which was carried out by researchers at the University of Innsbruck and IQOQI in Austria together with colleagues at the ICFO in Spain, challenges the idea that ultralow temperatures are a must for generating cat states. Instead of starting from the ground state, they used thermally excited states to show that quantum superpositions can exist at temperatures of up to 1.8 K – an environment that might as well be an oven in the quantum world.

Team leader Gerhard Kirchmair, a physicist at the University of Innsbruck and the IQOQI, says the study evolved from one of those “happy accidents” that characterize work in a collaborative environment. During a coffee break with a colleague, he realized he was well-equipped to prove the hypothesis of another colleague, Oriol Romero-Isart, who had shown theoretically that cat states can be generated out of a thermal state.

The experiment involved creating cat states inside a microwave cavity that acts as a quantum harmonic oscillator. This cavity is coupled to a superconducting transmon qubit that behaves as a two-level system where the superposition is generated. While the overall setup is cooled to 30 mK, the cavity mode itself is heated by equilibrating it with amplified Johnson-Nyquist noise from a resistor, making it 60 times hotter than its environment.

To establish the existence of quantum correlations at this higher temperature, the team directly measured the Wigner functions of the states. Doing so revealed the characteristic interference patterns of Schrödinger cat states.

Benefits for quantum sensing and error correction

According to Kirchmair, being able to realize cat states without ground-state cooling could bring benefits for quantum sensing. The mechanical oscillator systems used to sense acceleration or force, for example, are normally cooled to the ground state to achieve the necessary high sensitivity, but such extreme cooling may not be necessary. He adds that quantum error correction schemes could also benefit, as they rely on being able to create cat states reliably; the team’s work shows that a residual thermal population places fewer limitations on this than previously thought.

“For next steps we will use the system for what it was originally designed, i.e. to mediate interactions between multiple qubits for novel quantum gates,” he tells Physics World.

Yiwen Chu, a quantum physicist from ETH Zürich in Switzerland who was not involved in this research, praises the “creativeness of the idea”. She describes the results as interesting and surprising because they seem to counter the common view that lack of purity in a quantum state degrades quantum features. She also agrees that the work could be important for quantum sensing, adding that many systems – including some more suited for sensing – are difficult to prepare in the ground state.

However, Chu notes that, for reasons stemming from the system’s parameters and the protocols the team used to generate the cat states, it should be possible to cool this particular system very efficiently to the ground state. This, she says, somewhat diminishes the argument that the method will be useful for systems where this isn’t the case. “However, these parameters and the protocols they showed might not be the only way to prepare such states, so on a fundamental level it is still very interesting,” she concludes.

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Electron therapy has long played an important role in cancer treatments. Electrons with energies of up to 20 MeV can treat superficial tumours while minimizing delivered dose to underlying tissues; they are also ideal for performing total skin therapy and intraoperative radiotherapy. The limited penetration depth of such low-energy electrons, however, limits the range of tumour sites that they can treat. And as photon-based radiotherapy technology continues to progress, electron therapy has somewhat fallen out of fashion.

That could all be about to change with the introduction of radiation treatments based on very high-energy electrons (VHEEs). Once realised in the clinic, VHEEs – with energies from 50 up to 400 MeV – will deliver highly penetrating, easily steerable, conformal treatment beams with the potential to enable emerging techniques such as FLASH radiotherapy. French medical technology company THERYQ is working to make this opportunity a reality.

Therapeutic electron beams are produced using radio frequency (RF) energy to accelerate electrons within a vacuum cavity. An accelerator of a just over 1 m in length can boost electrons to energies of about 25 MeV – corresponding to a tissue penetration depth of a few centimetres. It’s possible to create higher energy beams by simply daisy chaining additional vacuum chambers. But such systems soon become too large and impractical for clinical use.

THERYQ is focusing on a totally different approach to generating VHEE beams. “In an ideal case, these accelerators allow you to reach energy transfers of around 100 MeV/m,” explains THERYQ’s Sébastien Curtoni. “The challenge is to create a system that’s as compact as possible, closer to the footprint and cost of current radiotherapy machines.”

Working in collaboration with CERN, THERYQ is aiming to modify CERN’s Compact Linear Collider technology for clinical applications. “We are adapting the CERN technology, which was initially produced for particle physics experiments, to radiotherapy,” says Curtoni. “There are definitely things in this design that are very useful for us and other things that are difficult. At the moment, this is still in the design and conception phase; we are not there yet.”

VHEE advantages

The higher energy of VHEE beams provides sufficient penetration to treat deep tumours, with the dose peak region extending up to 20–30 cm in depth for parallel (non-divergent) beams using energy levels of 100–150 MeV (for field sizes of 10 x 10 cm or above). And in contrast to low-energy electrons, which have significant lateral spread, VHEE beams have extremely narrow penumbra with sharp beam edges that help to create highly conformal dose distributions.

“Electrons are extremely light particles and propagate through matter in very straight lines at very high energies,” Curtoni explains. “If you control the initial direction of the beam, you know that the patient will receive a very steep and well defined dose distribution and that, even for depths above 20 cm, the beam will remain sharp and not spread laterally.”

Electrons are also relatively insensitive to tissue inhomogeneities, such as those encountered as the treatment beam passes through different layers of muscle, bone, fat or air. “VHEEs have greater robustness against density variations and anatomical changes,” adds THERYQ’s Costanza Panaino. “This is a big advantage for treatments in locations where there is movement, such as the lung and pelvic areas.”

It’s also possible to manipulate VHEEs via electromagnetic scanning. Electrons have a charge-to-mass ratio roughly 1800 times higher than that of protons, meaning that they can be steered with a much weaker magnetic field than required for protons. “As a result, the technology that you are building has a smaller footprint and the possibility costing less,” Panaino explains. “This is extremely important because the cost of building a proton therapy facility is prohibitive for some countries.”

Enabling FLASH

In addition to expanding the range of clinical indications that can be treated with electrons, VHEE beams can also provide a tool to enable the emerging – and potentially game changing – technique known as FLASH radiotherapy. By delivering therapeutic radiation at ultrahigh dose rates (higher than 100 Gy/s), FLASH vastly reduces normal tissue toxicity while maintaining anti-tumour activity, potentially minimizing harmful side-effects.

The recent interest in the FLASH effect began back in 2014 with the report of a differential response between normal and tumour tissue in mice exposed to high dose-rate, low-energy electrons. Since then, most preclinical FLASH studies have used electron beams, as did the first patient treatment in 2019 – a skin cancer treatment at Lausanne University Hospital (CHUV) in Switzerland, performed with the Oriatron eRT6 prototype from PMB-Alcen, the French company from which THERYQ originated.

FLASH radiotherapy is currently being used in clinical trials with proton beams, as well as with low-energy electrons, where it remains intrinsically limited to superficial treatments. Treating deep-seated tumours with FLASH requires more highly penetrating beams. And while the most obvious option would be to use photons, it’s extremely difficult to produce an X-ray beam with a high enough dose rate to induce the FLASH effect without excessive heat generation destroying the conversion target.

“It’s easier to produce a high dose-rate electron beam for FLASH than trying to [perform FLASH] with X-rays, as you use the electron beam directly to treat the patient,” Curtoni explains. “The possibility to treat deep-seated tumours with high-energy electron beams compensates for the fact that you can’t use X-rays.”

Panaino points out that in addition to high dose rates, FLASH radiotherapy also relies on various interdependent parameters. “Ideally, to induce the FLASH effect, the beam should be pulsed at a frequency of about 100 Hz, the dose-per-pulse should be 1 Gy or above, and the dose rate within the pulse should be higher than 10⁶ Gy/s,” she explains.

Into the clinic

THERYQ is using its VHEE expertise to develop a clinical FLASH radiotherapy system called FLASHDEEP, which will use electrons at energies of 100 to 200 MeV to treat tumours at depths of up to 20 cm. The first FLASHDEEP systems will be installed at CHUV (which is part of a consortium with CERN and THERYQ) and at the Gustave Roussy cancer centre in France.

“We are trying to introduce FLASH into the clinic, so we have a prototype FLASHKNiFE machine that allows us to perform low-energy, 6 and 9 MeV, electron therapy,” says Charlotte Robert, head of the medical physics department research group at Gustave Roussy. “The first clinical trials using low-energy electrons are all on skin tumours, aiming to show that we can safely decrease the number of treatment sessions.”

While these initial studies are limited to skin lesions, clinical implementation of the FLASHDEEP system will extend the benefits of FLASH to many more tumour sites. Robert predicts that VHEE-based FLASH will prove most valuable for treating radioresistant cancers that cannot currently be cured. The rationale is that FLASH’s ability to spare normal tissue will allow delivery of higher target doses without increasing toxicity.

“You will not use this technology for diseases that can already be cured, at least initially,” she explains. “The first clinical trial, I’m quite sure, will be either glioblastoma or pancreatic cancers that are not effectively controlled today. If we can show that VHEE FLASH can spare normal tissue more than conventional radiotherapy can, we hope this will have a positive impact on lesion response.”

“There are a lot of technological challenges around this technology and we are trying to tackle them all,” Curtoni concludes. “The ultimate goal is to produce a VHEE accelerator with a very compact beamline that makes this technology and FLASH a reality for a clinical environment.”

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Brain–computer interfaces (BCIs) enable the flow of information between the brain and an external device such as a computer, smartphone or robotic limb. Applications range from use in augmented and virtual reality (AR and VR), to restoring function to people with neurological disorders or injuries.

Electroencephalography (EEG)-based BCIs use sensors on the scalp to noninvasively record electrical signals from the brain and decode them to determine the user’s intent. Currently, however, such BCIs require bulky, rigid sensors that prevent use during movement and don’t work well with hair on the scalp, which affects the skin–electrode impedance. A team headed up at Georgia Tech’s WISH Center has overcome these limitations by creating a brain sensor that’s small enough to fit between strands of hair and is stable even while the user is moving.

“This BCI system can find wide applications. For example, we can realize a text spelling interface for people who can’t speak,” says W Hong Yeo, Harris Saunders Jr Professor at Georgia Tech and director of the WISH Center, who co-led the project with Tae June Kang from Inha University in Korea. “For people who have movement issues, this BCI system can offer connectivity with human augmentation devices, a wearable exoskeleton, for example. Then, using their brain signals, we can detect the user’s intentions to control the wearable system.”

A tiny device

The microscale brain sensor comprises a cross-shaped structure of five microneedle electrodes, with sharp tips (less than 30°) that penetrate the skin easily with nearly pain-free insertion. The researchers used UV replica moulding to create the array, followed by femtosecond laser cutting to shape it to the required dimensions – just 850 x 1000 µm – to fit into the space between hair follicles. They then coated the microsensor with a highly conductive polymer (PEDOT:Tos) to enhance its electrical conductivity.

The microneedles capture electrical signals from the brain and transmit them along ultrathin serpentine wires that connect to a miniaturized electronics system on the back of the neck. The serpentine interconnector stretches as the skin moves, isolating the microsensor from external vibrations and preventing motion artefacts. The miniaturized circuits then wirelessly transmit the recorded signals to an external system (AR glasses, for example) for processing and classification.

Yeo and colleagues tested the performance of the BCI using three microsensors inserted into the scalp of the occipital lobe (the brain’s visual processing centre). The BCI exhibited excellent stability, offering high-quality measurement of neural signals – steady-state visual evoked potentials (SSVEPs) – for up to 12 h, while maintaining low contact impedance density (0.03 kΩ/cm²).

The team also compared the quality of EEG signals measured using the microsensor-based BCI with those obtained from conventional gold-cup electrodes. Participants wearing both sensor types closed and opened their eyes while standing, walking or running.

With the participant stood still, both electrode types recorded stable EEG signals, with an increased amplitude upon closing the eyes, due to the rise in alpha wave power. During motion, however, the EEG time series recorded with the conventional electrodes showed noticeable fluctuations. The microsensor measurements, on the other hand, exhibited minimal fluctuations while walking and significantly fewer fluctuations than the gold-cup electrodes while running.

Overall, the alpha wave power recorded by the microsensors during eye-closing was higher than that of the conventional electrode, which could not accurately capture EEG signals while the user was running. The microsensors only exhibited minor motion artefacts, with little to no impact on the EEG signals in the alpha band, allowing reliable data extraction even during excessive motion.

Real-world scenario

Next, the team showed how the BCI could be used within everyday activities – such as making calls or controlling external devices – that require a series of decisions. The BCI enables a user to make these decisions using their thoughts, without needing physical input such as a keyboard, mouse or touchscreen. And the new microsensors free the user from environmental and movement constraints.

The researchers demonstrated this approach in six subjects wearing AR glasses and a microsensor-based EEG monitoring system. They performed experiments with the subjects standing, walking or running on a treadmill, with two distinct visual stimuli from the AR system used to induce SSVEP responses. Using a train-free SSVEP classification algorithm, the BCI determined which stimulus the subject was looking at with a classification accuracy of 99.2%, 97.5% and 92.5%, while standing, walking and running, respectively.

The team also developed an AR-based video call system controlled by EEG, which allows users to manage video calls (rejecting, answering and ending) with their thoughts, demonstrating its use during scenarios such as ascending and descending stairs and navigating hallways.

“By combining BCI and AR, this system advances communication technology, offering a preview of the future of digital interactions,” the researchers write. “Additionally, this system could greatly benefit individuals with mobility or dexterity challenges, allowing them to utilize video calling features without physical manipulation.”

The microsensor-based BCI is described in Proceedings of the National Academy of Sciences.

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With so much turmoil in the world at the moment, it’s always great to meet enthusiastic physicists celebrating all that their subject has to offer. That was certainly the case when I travelled with my colleague Tami Freeman to the 2025 Celebration of Physics at Nottingham Trent University (NTU) on 10 April.

Organized by the Institute of Physics (IOP), which publishes Physics World, the event was aimed at “physicists, creative thinkers and anyone interested in science”. It also featured some of the many people who won IOP awards last year, including Nick Stone from the University of Exeter, who was awarded the 2024 Rosalind Franklin medal and prize.

Stone was honoured for his “pioneering use of light for diagnosis and therapy in healthcare”, including “developing novel Raman spectroscopic tools and techniques for rapid in vivo cancer diagnosis and monitoring”. Speaking in a Physics World Live chat, Stone explained why Raman spectroscopy is such a useful technique for medical imaging.

Nottingham is, of course, a city famous for medical imaging, thanks in particular to the University of Nottingham Nobel laureate Peter Mansfield (1933–2017), who pioneered magnetic resonance imaging (MRI). In an entertaining talk, Rob Morris from NTU explained how MRI is also crucial for imaging foodstuffs, helping the food industry to boost productivity, reduce waste – and make tastier pork pies.

Still on the medical theme, Niall Holmes from Cerca Magnetics, which was spun out from the University of Nottingham, explained how his company has developed wearable magnetoencephalography (MEG) sensors that can measures magnetic fields generated by neuronal firings in the brain. In 2023 Cerca won one of the IOP’s business and innovation awards.

Richard Friend from the University of Cambridge, who won the IOP’s top Isaac Newton medal and prize, discussed some of the many recent developments that have followed from his seminal 1990 discovery that semiconducting polymers can be used in light-emitting diodes (LEDs).

The event ended with a talk from particle physicist Tara Shears from the University of Liverpool, who outlined some of the findings of the new IOP report Physics and AI, to which she was an adviser. Based on a survey with 700 responses and a workshop with experts from academia and industry, the report concludes that physics doesn’t only benefit from AI – but underpins it too.

I’m sure AI will be good for physics overall, but I hope it never removes the need for real-life meetings like the Celebration of Physics.

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Researchers from the Institute of Physics of the Chinese Academy of Sciences have produced the first two-dimensional (2D) sheets of metal. At just angstroms thick, these metal sheets could be an ideal system for studying the fundamental physics of the quantum Hall effect, 2D superfluidity and superconductivity, topological phase transitions and other phenomena that feature tight quantum confinement. They might also be used to make novel electronic devices such as ultrathin low-power transistors, high-frequency devices and transparent displays.

Since the discovery of graphene – a 2D sheet of carbon just one atom thick – in 2004, hundreds of other 2D materials have been fabricated and studied. In most of these, layers of covalently-bonded atoms are separated by gaps. The presence of these gaps mean that neighbouring layers are held together only by weak van der Waals (vdW) interactions, making it relatively easy to “shave off” single layers to make 2D sheets.

Making atomically thin metals would expand this class of technologically important structures. However, because each atom in a metal is strongly bonded to surrounding atoms in all directions, thinning metal sheets to this degree has proved difficult. Indeed, many researchers thought it might be impossible.

Melting and squeezing pure metals

The technique developed by Guangyu Zhang, Luojun Du and colleagues involves heating powders of pure metals between two monolayer-MoS₂/sapphire vdW anvils. The team used MoS₂/sapphire because both materials are atomically flat and lack dangling bonds that could react with the metals. They also have high Young’s moduli, of 430 GPa and 300 GPa respectively, meaning they can withstand extremely high pressures.

Once the metal powders melted into a droplet, the researchers applied a pressure of 200 MPa. They then continued this “vdW squeezing” until the opposite sides of the anvils cooled to room temperature and 2D sheets of metal formed.

The team produced five atomically thin 2D metals using this technique. The thinnest, at around 6.3 Å, was bismuth, followed by tin (~5.8 Å), lead (~7.5 Å), indium (~8.4 Å) and gallium (~9.2 Å).

“Arduous explorations”

Zhang, Du and colleagues started this project around 10 years ago after they decided it would be interesting to work on 2D materials other than graphene and its layered vdW cousins. At first, they had little success. “Since 2015, we tried out a host of techniques, including using a hammer to thin a metal foil – a technique that we borrowed from gold foil production processes – all to no avail,” Du recalls. “We were not even able to make micron-thick foils using these techniques.”

After 10 years of what Du calls “arduous explorations”, the team finally moved a crucial step forward by developing the vdW squeezing method.

Writing in Nature, the researchers say that the five 2D metals they’ve realized so far are just the “tip of the iceberg” for their method. They now intend to increase this number. “In terms of novel properties, there is still a knowledge gap in the emerging electrical, optical, magnetic properties of 2D metals, so it would be nice to see how these materials behave physically as compared to their bulk counterparts thanks to 2D confinement effects,” says Zhang. “We would also like to investigate to what extent such 2D metals could be used for specific applications in various technological fields.”

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A proposed experiment that would involve trapping atoms on a two-layered laser grid could be used to study the mechanism behind high-temperature superconductivity. Developed by physicists in Germany and France led by Henning Schlömer the new techniques could revolutionize our understanding of high-temperature superconductivity.

Superconductivity is a phenomenon characterized by an abrupt drop to zero of electric resistance when certain materials are cooled below a critical temperature. It has remained in the physics zeitgeist for over a hundred years and continues to puzzle contemporary physicists. While scientists have a good understanding of “conventional” superconductors (which tend to have low critical temperatures), the physics of high-temperature superconductors remains poorly understood.  A deeper understanding of the mechanisms responsible for high-temperature superconductivity could unveil the secrets behind macroscopic quantum phenomena in many-body systems.

Mimicking real crystalline materials

Optical lattices have emerged as a powerful tool to study such many-body quantum systems. Here, two counter-propagating laser beams overlap to create a standing wave. Extending this into two dimensions creates a grid (or lattice) of potential-energy minima where atoms can be trapped (see figure). The interactions between these trapped atoms can then be tuned to mimic real crystalline materials giving us an unprecedented ability to study their properties.

Superconductivity is characterized by the formation of long-range correlations between electron pairs. While the electronic properties of high-temperature superconductors can be studied in the lab, it can be difficult to test hypotheses because the properties of each superconductor are fixed. In contrast, correlations between atoms in an optical lattice can be tuned, allowing different models and parameters to be explored.

This could be done by trapping fermionic atoms (analogous to electrons in a superconducting material) in an optical lattice and enabling them to form pair correlations. However, this has proved to be challenging because these correlations only occur at very low temperatures that are experimentally inaccessible. Measuring these correlations presents an additional challenge of adding or removing atoms at specific sites in the lattice without disturbing the overall lattice state. But now, Schlömer and colleagues propose a new protocol to overcome these challenges.

The proposal

The researchers propose trapping fermionic atoms on a two-layered lattice. By introducing a potential-energy offset between the two layers, they ensure that the atoms can only move within a layer and there is no hopping between layers. They enable magnetic interaction between the two layers, allowing the atoms to form spin-correlations such as singlets, where atoms always have opposing spins . The dynamics of such interlayer correlations will give rise to superconducting behaviour.

This system is modelled using a “mixed-dimensional bilayer” (MBD) model. It accounts for three phenomena: the hopping of atoms between lattice sites within a layer; the magnetic (spin) interaction between the atoms of the two layers; and the magnetic interactions within the atoms of a layer.

Numerical simulations of the MBD model suggest the occurrence of superconductor-like behaviour in optical lattices at critical temperatures much higher than traditional models. These temperatures are readily accessible in experiments.

To measure the correlations, one needs to track pair formation in the lattice. One way to track pairs is to add or remove atoms from the lattice without disturbing the overall lattice state. However, this is experimentally infeasible. Instead, the researchers propose doping the energetically higher layer with holes – that is the removal of atoms to create vacant sites. The energetically lower layer is doped with doublons, which are atom pairs that occupy just one lattice site. Then the potential offset between the two layers can be tuned to enable controlled interaction between the doublons and holes. This would allow researchers to study pair formation via this interaction rather than having to add or remove atoms from specific lattice sites.

Clever mathematical trick

To study superconducting correlations in the doped system, the researchers employ a clever mathematical trick. Using a mathematical transformation, they transform the model to an equivalent model described by only “hole-type” dopants without changing the underlying physics. This allows them to map superconducting correlations to density correlations, which can be routinely accessed is existing experiments.

With their proposal, Schlömer and colleagues are able to both prepare the optical lattice in a state, where superconducting behaviour occurs at experimentally accessible temperatures and study this behaviour by measuring pair formation.

When asked about possible experimental realizations, Schlömer is optimistic: “While certain subtleties remain to be addressed, the technology is already in place – we expect it will become experimental reality in the near future”.

The research is described in PRX Quantum

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Imagine, if you will, that you are a quantum system. Specifically, you are an unstable quantum system – one that would, if left to its own devices, rapidly decay from one state (let’s call it “awake”) into another (“asleep”). But whenever you start to drift into the “asleep” state, something gets in the way. Maybe it’s a message pinging on your phone. Maybe it’s a curious child peppering you with questions. Whatever it is, it jolts you out of your awake–asleep superposition and projects you back into wakefulness. And because it keeps happening faster than you can fall asleep, you remain awake, diverted from slumber by a stream of interruptions – or, in quantum terms, measurements.

This phenomenon of repeated measurements “freezing” an unstable quantum system into a particular state is known as the quantum Zeno effect (figure 1). Named after a paradox from ancient Greek philosophy, it was hinted at in the 1950s by the scientific polymaths Alan Turing and John von Neumann but only fully articulated in 1977 by the physicists Baidyanath Misra and George Sudarshan (J. Math. Phys. 18 756). Since then, researchers have observed it in dozens of quantum systems, including trapped ions, superconducting flux qubits and atoms in optical cavities. But the apparent ubiquitousness of the quantum Zeno effect cannot hide the strangeness at its heart. How does the simple act of measuring a quantum system have such a profound effect on its behaviour?

A watched quantum pot

“When you come across it for the first time, you think it’s actually quite amazing because it really shows that the measurement in quantum mechanics influences the system,” says Daniel Burgarth, a physicist at the Friedrich-Alexander-Universität in Erlangen-Nürnberg, Germany, who has done theoretical work on the quantum Zeno effect.

Giovanni Barontini, an experimentalist at the University of Birmingham, UK, who has studied the quantum Zeno effect in cold atoms, agrees. “It doesn’t have a classical analogue,” he says. “I can watch a classical system doing something forever and it will continue doing it. But a quantum system really cares if it’s watched.”

For the physicists who laid the foundations of quantum mechanics a century ago, any connection between measurement and outcome was a stumbling block. Several tried to find ways around it, for example by formalizing a role for observers in quantum wavefunction collapse (Niels Bohr and Werner Heisenberg); introducing new “hidden” variables (Louis de Broglie and David Bohm); and even hypothesizing the creation of new universes with each measurement (the “many worlds” theory of Hugh Everett).

But none of these solutions proved fully satisfactory. Indeed, the measurement problem seemed so intractable that most physicists in the next generation avoided it, preferring the approach sometimes described – not always pejoratively – as “shut up and calculate”.

Today’s quantum physicists are different. Rather than treating what Barontini calls “the apotheosis of the measurement effect” as a barrier to overcome or a triviality to ignore, they are doing something few of their forebears could have imagined. They are turning the quantum Zeno effect into something useful.

Noise management

To understand how freezing a quantum system by measuring it could be useful, consider a qubit in a quantum computer. Many quantum algorithms begin by initializing qubits into a desired state and keeping them there until they’re required to perform computations. The problem is that quantum systems seldom stay where they’re put. In fact, they’re famously prone to losing their quantum nature (decohering) at the slightest disturbance (noise) from their environment. “Whenever we build quantum computers, we have to embed them in the real world, unfortunately, and that real world causes nothing but trouble,” Burgarth says.

Quantum scientists have many strategies for dealing with environmental noise. Some of these strategies are passive, such as cooling superconducting qubits with dilution refrigerators and using electric and magnetic fields to suspend ionic and atomic qubits in a vacuum. Others, though, are active. They involve, in effect, tricking qubits into staying in the states they’re meant to be in, and out of the states they’re not.

The quantum Zeno effect is one such trick. “The way it works is that we apply a sequence of kicks to the system, and we are actually rotating the qubit with each kick,” Burgarth explains. “You’re rotating the system, and then effectively the environment wants to rotate it in the other direction.” Over time, he adds, these opposing rotations average out, protecting the system from noise by freezing it in place.

Quantum state engineering

While noise mitigation is useful, it’s not the quantum Zeno application that interests Burgarth and Barontini the most. The real prize, they agree, is something called quantum state engineering, which is much more complex than simply preventing a quantum system from decaying or rotating.

The source of this added complexity is that real quantum systems – much like real people – usually have more than two states available to them. For example, the set of permissible “awake” states for a person – the Hilbert space of wakefulness, let’s call it – might include states such as cooking dinner, washing dishes and cleaning the bathroom. The goal of quantum state engineering is to restrict this state-space so the system can only occupy the state(s) required for a particular application.

As for how the quantum Zeno effect does this, Barontini explains it by referring to Zeno’s original, classical paradox. In the fifth century BCE, the philosopher Zeno of Elea posed a conundrum based on an arrow flying through the air. If you look at this arrow at any possible moment during its flight, you will find that in that instant, it is motionless. Yet somehow, the arrow still moves. How?

In the quantum version, Barontini explains, looking at the arrow freezes it in place. But that isn’t the only thing that happens. “The funniest thing is that if I look somewhere, then the arrow cannot go where I’m looking,” he says. “It will have to go around it. It will have to modify its trajectory to go outside my field of view.”

By shaping this field of view, Barontini continues, physicists can shape the system’s behaviour. As an example, he cites work by Serge Haroche, who shared the 2012 Nobel Prize for Physics with another notable quantum Zeno experimentalist, David Wineland.

In 2014 Haroche and colleagues at the École Normale Supérieure (ENS) in Paris, France, sought to control the dynamics of an electron within a so-called Rydberg atom. In this type of atom, the outermost electron is very weakly bound to the nucleus and can occupy any of several highly excited states.

The researchers used a microwave field to divide 51 of these highly excited Rydberg states into two groups, before applying radio-frequency pulses to the system. Normally, these pulses would cause the electron to hop between states. However, the continual “measurement” supplied by the microwave field meant that although the electron could move within either group of states, it could not jump from one group to the other. It was stuck – or, more precisely, it was in a special type of quantum superposition known as a Schrödinger cat state.

Restricting the behaviour of an electron might not sound very exciting in itself. But in this and other experiments, Haroche and colleagues showed that imposing such restrictions brings forth a slew of unusual quantum states. It’s as if telling the system what it can’t do forces it to do a bunch of other things instead, like a procrastinator who cooks dinner and washes dishes to avoid cleaning the bathroom. “It really enriches your quantum toolbox,” explains Barontini. “You can generate an entangled state that is more entangled or methodologically more useful than other states you could generate with traditional means.”

Just what is a measurement, anyway?

As well as generating interesting quantum states, the quantum Zeno effect is also shedding new light on the nature of quantum measurements. The question of what constitutes a “measurement” for quantum Zeno purposes turns out to be surprisingly broad. This was elegantly demonstrated in 2014, when physicists led by Augusto Smerzi at the Università di Firenze, Italy, showed that simply shining a resonant laser at their quantum system (figure 2) produced the same quantum Zeno dynamics as more elaborate “projective” measurements – which in this case involved applying pairs of laser pulses to the system at frequencies tailored to specific atomic transitions. “It’s fair to say that almost anything causes a Zeno effect,” says Burgarth. “It’s a very universal and easy-to-trigger phenomenon.”

Other research has broadened our understanding of what measurement can do. While the quantum Zeno effect uses repeated measurements to freeze a quantum system in place (or at least slow its evolution from one state to another), it is also possible to do the opposite and use measurements to accelerate quantum transitions. This phenomenon is known as the quantum anti-Zeno effect, and it has applications of its own. It could, for example, speed up reactions in quantum chemistry.

Over the past 25 years or so, much work has gone into understanding where the ordinary quantum Zeno effect leaves off and the quantum anti-Zeno effect begins. Some systems can display both Zeno and anti-Zeno dynamics, depending on the frequency of the measurements and various environmental conditions. Others seem to favour one over the other.

But regardless of which version turns out to be the most important, quantum Zeno research is anything but frozen in place. Some 2500 years after Zeno posed his paradox, his intellectual descendants are still puzzling over it.

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With increased water scarcity and global warming looming, electrochemical technology offers low-energy mitigation pathways via desalination and carbon capture.  This webinar will demonstrate how the less than 5 molar solid-state concentration swings afforded by cation intercalation materials – used originally in rocking-chair batteries – can effect desalination using Faradaic deionization (FDI).  We show how the salt depletion/accumulation effect – that plagues Li-ion battery capacity under fast charging conditions – is exploited in a symmetric Na-ion battery to achieve seawater desalination, exceeding by an order of magnitude the limits of capacitive deionization with electric double layers.  While initial modeling that introduced such an architecture blazed the trail for the development of new and old intercalation materials in FDI, experimental demonstration of seawater-level desalination using Prussian blue analogs required cell engineering to overcome the performance-degrading processes that are unique to the cycling of intercalation electrodes in the presence of flow, leading to innovative embedded, micro-interdigitated flow fields with broader application toward fuel cells, flow batteries, and other flow-based electrochemical devices.  Similar symmetric FDI architectures using proton intercalation materials are also shown to facilitate direct-air capture of carbon dioxide with unprecedentedly low energy input by reversibly shifting pH within aqueous electrolyte.

Kyle C Smith joined the faculty of Mechanical Science and Engineering at the University of Illinois Urbana-Champaign (UIUC) in 2014 after completing his PhD in mechanical engineering (Purdue, 2012) and his post-doc in materials science and engineering (MIT, 2014).  His group uses understanding of flow, transport, and thermodynamics in electrochemical devices and materials to innovate toward separations, energy storage, and conversion.  For his research he was awarded the 2018 ISE-Elsevier Prize in Applied Electrochemistry of the International Society of Electrochemistry and the 2024 Dean’s Award for Early Innovation as an associate professor by UIUC’s Grainger College.  Among his 59 journal papers and 14 patents and patents pending, his work that introduced Na-ion battery-based desalination using porous electrode theory [Smith and Dmello, J. Electrochem. Soc., 163, p. A530 (2016)] was among the top ten most downloaded in the Journal of the Electrochemical Society for five months in 2016.  His group was also the first to experimentally demonstrate seawater-level salt removal using this approach [Do et al., Energy Environ. Sci., 16, p. 3025 (2023); Rahman et al., Electrochimica Acta, 514, p. 145632 (2025)], introducing flow fields embedded in electrodes to do so.

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A model that could help explain how heavy elements are forged within collapsing stars has been unveiled by Matthew Mumpower at Los Alamos National Laboratory and colleagues in the US. The team suggests that energetic photons generated by newly forming black holes or neutron stars transmute protons within ejected stellar material into neutrons, thereby providing ideal conditions for heavy elements to form.

Astrophysicists believe that elements heavier than iron are created in violent processes such as the explosions of massive stars and the mergers of neutron stars. One way that this is thought to occur is the rapid neutron-capture process (r-process), whereby lighter nuclei created in stars capture neutrons in rapid succession. However, exactly where the r-process occurs is not well understood.

As Mumpower explains, the r-process must be occurring in environments where free neutrons are available in abundance. “But there’s a catch,” he says. “Free neutrons are unstable and decay in about 15 min. Only a few places in the universe have the right conditions to create and use these neutrons quickly enough. Identifying those places has been one of the toughest open questions in physics.”

Intense flashes of light

In their study, Mumpower’s team – which included researchers from the Los Alamos and Argonne national laboratories – looked at how lots of neutrons could be created within massive stars that are collapsing to become neutron stars or black holes. Their idea focuses on the intense flashes of light that are known to be emitted from the cores of these objects.

This radiation is emitted at wavelengths across the electromagnetic spectrum – including highly energetic gamma rays. Furthermore, the light is emitted along a pair of narrow jets, which blast outward above each pole of the star’s collapsing core. As they form, these jets plough through the envelope of stellar material surrounding the core, which had been previously ejected by the star. This is believed to create a “cocoon” of hot, dense material surrounding each jet.

In this environment, Mumpower’s team suggest that energetic photons in a jet collide with protons to create a neutron and a pion. Since these neutrons are have no electrical charge, many of them could dissolve into the cocoon, providing ideal conditions for the r-process to occur.

To test their hypothesis, the researchers carried out detailed computer simulations to predict the number of free neutrons entering the cocoon due to this process.

Gold and platinum

“We found that this light-based process can create a large number of neutrons,” Mumpower says. “There may be enough neutrons produced this way to build heavy elements, from gold and platinum all the way up to the heaviest elements in the periodic table – and maybe even beyond.”

If their model is correct, suggests that the origin of some heavy elements involves processes that are associated with the high-energy particle physics that is studied at facilities like the Large Hadron Collider.

“This process connects high-energy physics – which usually focuses on particles like quarks, with low-energy astrophysics – which studies stars and galaxies,” Mumpower says. “These are two areas that rarely intersect in the context of forming heavy elements.”

Kilonova explosions

The team’s findings also shed new light on some other astrophysical phenomena. “Our study offers a new explanation for why certain cosmic events, like long gamma-ray bursts, are often followed by kilonova explosions – the glow from the radioactive decay of freshly made heavy elements,” Mumpower continues. “It also helps explain why the pattern of heavy elements in old stars across the galaxy looks surprisingly similar.”

The findings could also improve our understanding of the chemical makeup of deep-sea deposits on Earth. The presence of both iron and plutonium in this material suggests that both elements may have been created in the same type of event, before coalescing into the newly forming Earth.

For now, the team will aim to strengthen their model through further simulations – which could better reproduce the complex, dynamic processes taking place as massive stars collapse.

The research is described in The Astrophysical Journal.

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The US administration is carrying out “a wholesale assault on US science” that could hold back research in the country for several decades. That is the warning from more than 1900 members of the US National Academies of Sciences, Engineering, and Medicine, who have signed an open letter condemning the policies introduced by Donald Trump since he took up office on 20 January.

US universities are in the firing line of the Trump administration, which is seeking to revoke the visas of foreign students, threatening to withdraw grants and demanding control over academic syllabuses. “The voice of science must not be silenced,” the letter writers say. “We all benefit from science, and we all stand to lose if the nation’s research enterprise is destroyed.”

Particularly hard hit are the country’s eight Ivy League universities, which have been accused of downplaying antisemitism exhibited in campus demonstrations in support of Gaza. Columbia University in New York, for example, has been trying to regain $400m in federal funds that the Trump administration threatened to cancel.

Columbia initially reached an agreement with the government on issues such as banning facemasks on its campus and taking control of its department responsible for courses on the Middle East. But on 8 April, according to reports, the National Institutes of Health, under orders from the Department of Health and Human Services, blocked all of its grants to Columbia.

Harvard University, meanwhile, has announced plans to privately borrow $750m after the Trump administration announced that it would review $9bn in the university’s government funding. Brown University in Rhode Island faces a loss of $510m, while the government has suspended several dozen research grants for Princeton University.

The administration also continues to oppose the use of diversity, equity and inclusion (DEI) programmes in universities. The University of Pennsylvania, from which Donald Trump graduated, faces the suspension of $175m in grants for offences against the government’s DEI policy.

Brain drain

Researchers in medical and social sciences are bearing the brunt of government cuts, with physics departments seeing relatively little impact on staffing and recruitment so far. “Of course we are concerned,” Peter Littlewood, chair of the University of Chicago’s physics department, told Physics World. “Nonetheless, we have made a deliberate decision not to halt faculty recruiting and stand by all our PhD offers.”

David Hsieh, executive officer for physics at California Institute of Technology, told Physics World that his department has also not taken any action so far. “I am sure that each institution is preparing in ways that make the most sense for them,” he says. “But I am not aware of any collective response at the moment.”

Yet universities are already bracing themselves for a potential brain drain. “The faculty and postdoc market is international, and the current sentiment makes the US less attractive for reasons beyond just finance,” warns Littlewood at Chicago.

That sentiment is echoed by Maura Healey, governor of Massachusetts, who claims that Europe, the Middle East and China are already recruiting the state’s best and brightest. “[They’re saying] we’ll give you a lab; we’ll give you staff. We’re giving away assets to other countries instead of training them, growing them [and] supporting them here.”

Science agencies remain under pressure too. The Department of Government Efficiency, run by Elon Musk, has already  ended $420m in “unneeded” NASA contracts. The administration aims to cut the year’s National Science Foundation (NSF) construction budget, with data indicating that the agency has roughly halved its number of new grants since Trump became president.

Yet a threat to reduce the percentage of ancillary costs related to scientific grants appeared at least on hold, for now at least. “NSF awardees may continue to budget and charge indirect costs using either their federally negotiated indirect cost rate agreement or the “de minimis” rate of 15%, as authorized by the uniform guidance and other Federal regulations,” says an NSF spokesperson.

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Researchers at the SLAC National Accelerator Laboratory in the US have produced the world’s most powerful ultrashort electron beam to date, concentrating petawatt-level peak powers into femtosecond-long pulses at an energy of 10 GeV and a current of around 0.1 MA. According to officials at SLAC’s Facility for Advanced Accelerator Experimental Tests (FACET-II), the new beam could be used to study phenomena in materials science, quantum physics and even astrophysics that were not accessible before.

High-energy electron beams are routinely employed as powerful probes in several scientific fields. To produce them, accelerator facilities like SLAC use strong electric fields to accelerate, focus and compress bunches of electrons. This is not easy, because as electrons are accelerated and compressed, they emit radiation and lose energy, causing the beam’s quality to deteriorate.

An optimally compressed beam

To create their super-compressed ultrashort beam, researchers led by Claudio Emma at FACET-II used a laser to shape the electron bunch’s profile with millimetre-scale precision in the first 10 metres of the accelerator, when the beam’s energy is lowest. They then took this modulated electron beam and boosted its energy by a factor of 100 in a kilometre-long stretch of downstream accelerating cavities. The last step was to compress the beam by a factor of 1000 by using magnets to turn the beam’s millimetre-scale features into a micron-sized long current spike.

One of the biggest challenges, Emma says, was to optimise the laser-based modulation of the beam in tandem with the accelerating cavity and magnetic fields of the magnets to obtain the optimally compressed beam at the end of the accelerator. “This was a large parameter space to work in with lots of knobs to turn and it required careful iteration before an optimum was found,” Emma says.

Measuring the ultra-short electron bunches was also a challenge. “These are typically so intense that if you intercept them with, for example, scintillating screens (a typical technique used in accelerators to diagnose properties of the beam like its spot size or bunch length), the beam fields are so strong they can melt these screens,” Emma explains. “To overcome this, we had to use a series of indirect measurements (plasma ionisation and beam-based radiation) along with simulations to diagnose just how strongly compressed and powerful these beams were.”

Beam delivery

According to Emma, generating extremely compressed electron beams is one of the most important challenges facing accelerator and beam physicists today. “It was interesting for us to tackle this challenge at FACET-II, which is a facility designed specifically to do this kind of research on extreme beam manipulation,” he says.

The team has already delivered the new high-current beams to experimenters who work on probing and optimising the dynamics of plasma-based accelerators. Further down the line, they anticipate much wider applications. “In the future we imagine that we will attract interest from users in multiple fields, be they materials scientists, strong-field quantum physicists or astrophysicists, who want to use the beam as a strong relativistic ‘hammer’ to study and probe a variety of natural interactions with the unique tool that we can provide,” Emma tells Physics World.

The researchers’ next step will be to increase the beam’s current by another order of magnitude. “This additional leap will require the use of a different plasma-based compression technique, rather than the current laser-based approach, which we hope to demonstrate at FACET-II in the near future,” Emma reveals.

The present work is described in Physical Review Letters.

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Researchers from China, the UK and Singapore have demonstrated for the first time that choosing the right set of initial conditions can speed up the relaxation process in quantum systems. Their experiments using single trapped ions are a quantum analogue of the classical Mpemba effect, in which hot water can, under certain circumstances, cool faster than cold water. By showing that it is possible to exponentially accelerate the relaxation of a pure state into a stationary state – the hallmark of the so-called strong Mpemba effect – they also provide strategies for designing and analysing open quantum systems such as those used in quantum batteries.

In both the classical and the quantum worlds, the difference between the relaxation process of a system in a strong Mpemba effect (sME) state and any other state is that the decay rate of a sME state is greater than the others. This naturally leads to the conclusion that initial conditions influence the speed at which a system will reach equilibrium. However, the mathematics of the quantum and classical sME are different. While in the classical world an open system is described by the Fokker-Planck equation, with the temperature as the key variable, in the quantum world the Lindblad master equation applies, and the energy of the sME state is what matters.

Paths and overlap

To understand why a quantum system in a particular initial state reaches a steady state faster than any other, we should think about the possible paths that a system can take. One key path is known as the slowest decay mode (SDM), which is the path that takes the system the most time to decay. At the other extreme, the fastest relaxation path is the one taken by a system in the sME initial state. This relaxation path must avoid any overlap with the SDM’s path.

Hui Jing, a physicist at China’s Hunan Normal University who co-led the study, points out that a fundamental characteristic of the quantum sME is that its relaxation path includes the so-called Liouvillian exceptional point (LEP). At this point, an eigenvalue of the dynamical generator, which is the Liovillian superoperator that describes the time evolution of the open quantum system through the Lindblad master equation, changes from real to complex.  When the eigenvalue of the SDM is real, the system is successfully prepared in the sME. When the eigenvalue of the SDM acquires an imaginary part, the overlap between the prepared sME state and the SDM is no longer zero. The LEP therefore signals the transition from strong to weak Mpemba effect.

Experimental set-up

To create a pure state that presents zero overlap with the SDM in an open quantum system, Jing and colleagues trapped a ⁴⁰Ca⁺ ion and coupled three of its energy levels through laser interactions.  The first laser beam, with a wavelength of 729 nm, coupled the ground state with the two excited states with coupling strengths characterized by Rabi frequencies Ω₁ and Ω₂. A second, circularly polarized laser beam at 854 nm controlled the decay between the first excited state and the ground state.

By tuning the Rabi frequencies, researchers were able to explore different relaxation regimes of the system. When the ratio between the Rabi frequencies was much smaller or bigger than the LEP, they observed the sME and weak ME, respectively.  When the ratio equalled the LEP, the transition from sME to weak ME took place.

This work, which is described in Nature Communications, marks the first experimental realization of the quantum strong Mpemba effect. According to Jing, the team’s methods offer an experimental alternative to existing ways of increasing the ion cooling rate or enhancing the efficiency of quantum batteries. Now, the group plans to study how the quantum Mpemba effect behaves at the LEP, since this point could lead to faster decay rates.

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“Fusion is now within reach” and represents “one of the economic opportunities of the century”. Not the words of an optimistic fusion scientist but from Kerry McCarthy, parliamentary under-secretary of state at the UK’s Department for Energy Security and Net Zero.

She was speaking on Tuesday at the inaugural Fusion Fest by Economist Impact. Held in London, the day-long event featured 400 attendees and more than 60 speakers from around the world.

McCarthy outlined several initiatives to keep the UK at the “forefront of fusion”. That includes investing £20m into Starmaker One, a £100m endeavour announced in early April to kickstart UK investment fusion fund.

The usual cliché is that fusion is always being 20 years away, perhaps not helped by large international projects such as the ITER experimental fusion reactor that is currently being built in Cadarache, France, which has struggling with delays and cost hikes.

Yet many delegates at the meeting were optimistic that significant developments are within reach with private firms racing to demonstrate “breakeven” – generating more power out than needed to fuel the reaction. Some expect “a few” private firms to announce breakeven by 2030.

And these aren’t small ventures. Commonwealth Fusion Systems, based in Massachusetts, US, for example, has 1300 people. Yet large international companies are, for the moment, only dipping their toe into the fusion pool.

While some $8bn has already been spent by private firms on fusion, many expect the funding floodgates to open once breakeven has been achieved in a private lab.

Most stated that a figure of about $50-60bn, however, would be needed to make fusion a real endeavour in terms of delivering power to the grid, something that could happen in the 2040s. But it was reiterated throughout the day that fusion must provide energy at a price that consumers would be willing to pay.

On target

It is not only private firms that are making progress. Many will point out that ITER has laid much of the groundwork in terms of fostering a fusion “ecosystem” – a particular buzzword of the day – that was demonstrated, in part, by the significant attendence at the event.

And developments are not just being confined to magnetic fusion. Kim Budil, director of the Lawrence Livermore National Laboratory, which is home to the National Ignition Facility, noted that the machine had recently achieved a fusion gain for the eighth time.

In a recent shot, she said that the device had produced 7 MJ with about 2 MJ having been delivered to the small capsule target. This represents a gain of about 3.4 – much more than its previous record of 2.4.

NIF, which is based on inertial confinement fusion rather than magnetic confinement, is currently undergoing refurbishment and upgrades. It is hoped that this will increase the energy input to about 2.6 MJ but gains of between 10-15 will be demonstrated if the technique can go anywhere.

Despite the number of fusion firms ballooning from a handful in the early 2010s to some 30 today, the general feeling at the meeting was that only a few will likely go on to build power plants, with the remainder using fusion for other sectors.

The issue is that no-one knew what technology would likely succeed, so all to play for.

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This episode of the Physics World Weekly podcast features an interview with Panicos Kyriacou, who is chief scientist at the UK-based start-up Crainio. The company has developed a non-invasive way of using light to measure the pressure inside the skull. Knowing this intracranial pressure is crucial when diagnosing traumatic brain injury, which a leading cause of death and disability. Today, the only way to assess intracranial pressure is to insert a sensor into the patient’s brain, so Crainio’s non-invasive technique could revolutionize how brain injuries are diagnosed and treated.

Kyriacou tells Physics World’s Tami Freeman why it is important to assess a patient’s intracranial pressure as soon as possible after a head injury. He explains how Crainio’s optical sensor measures blood flow in the brain and then uses machine learning to deduce the intracranial pressure.

Kyriacou is also professor of engineering at City St George’s University of London, where the initial research for the sensor was done. He recalls how Crainio was spun out of the university and how it is currently in a second round of clinical trials.

As well as being non-invasive, Crainio’s technology could reduce the cost of determining intracranial pressure and make it possible to make measurements in the field, shortly after injuries occur.

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Andrew Martin, skills policy lead at the UK’s Department for Science, Innovation and Technology (DSIT), flashed up a slide. Speaking at the ninth Careers in Quantum event in Bristol last week, he listed the eight skills that the burgeoning quantum-technology sector wants. Five are various branches of engineering, including electrical and electronics, mechanical, software and systems. A sixth is materials science and chemistry, with a seventh being quality control.

Quantum companies, of course, do also want “quantum specialists”, which was the eighth skill identified by Martin. But it’s a sign of how mature the sector has become that being a hotshot quantum physicist is no longer the only route in. That point was underlined by Carlos Faurby, a hardware integration engineer at Sparrow Quantum in Denmark, which makes single-photon sources for quantum computers. “You don’t need a PhD in physics to work at Sparrow,” Faurby declared.

Quantum tech certainly has a plethora of career options, with the Bristol event featuring a selection of firms from across the quantum ecosystem. Some are making prototype quantum computers (Quantum Motion, Quantinuum, Oxford Ionics) or writing the algorithms to run on quantum computers (Phasecraft). Others are building quantum networks (BT, Toshiba), working on quantum error correction (Riverlane) or developing quantum cryptography (KETS Quantum). Businesses building hardware such as controllers and modems were present too.

With the 2025 International Year of Quantum Science and Technology (IYQ) now in full swing, the event underlined just how thriving the sector is, with lots of career choices for physicists – whether you have a PhD or not. But competition to break in is intense. Phasecraft says it gets 50–100 applicants for each student internship it offers, with Riverlane receiving almost 200 applications for two summer placements.

That’s why it’s vital for physics students to develop their “soft skills” – or “professional skills” as several speakers preferred to call them. Team working, project management, collaboration and communication are all essential for jobs in the quantum industry, as indeed they are for all careers. Sadly, many physicists don’t realize soon enough just how crucial soft skills are.

Reflecting on his time at Light Trace Photonics, which he co-founded in 2021, Dominic Sulway joked in a panel discussion that he’d “enjoyed developing all the skills people told me I’d need for my PhD”. Of course, if you really want to break into the sector, why not follow his lead and start a business yourself? It’s a rewarding experience, I was told, and there doesn’t seem to be any slow-down in the number of quantum firms starting up.

• For more information on career options for physicists, check out the free-to-read 2025 Physics World Careers guide

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A quantum computer has been used for the first time to generate strings of certifiably random numbers. The protocol for doing this, which was developed by a team that included researchers at JPMorganChase and the quantum computing firm Quantinuum, could have applications in areas ranging from lotteries to cryptography – leading Quantinuum to claim it as quantum computing’s first commercial application, though other firms have made similar assertions. Separately, Quantinuum and its academic collaborators used the same trapped-ion quantum computer to explore problems in quantum magnetism and knot theory.

Genuinely random numbers are important in several fields, but classical computers cannot create them. The best they can do is to generate apparently random or “pseudorandom” numbers. Randomness is inherent in the laws of quantum mechanics, however, so quantum computers are naturally suited to random number generation. In fact, random circuit sampling – in which all qubits are initialized in a given state and allowed to evolve via quantum gates before having their states measured at the output – is often used to benchmark their power.

Of course, not everyone who wants to produce random numbers will have their own quantum computer. However, in 2023 Scott Aaronson of the University of Texas at Austin, US and his then-PhD student Shi-Han Hung suggested that a client could send a series of pseudorandomly chosen “challenge” circuits to a central server. There, a quantum computer could perform random circuit sampling before sending the readouts to the client.

If these readouts are truly the product of random circuit sampling measurements performed on a quantum computer, they will be truly random numbers. “Certifying the ‘quantumness’ of the output guarantees its randomness,” says Marco Pistoia, JPMorganChase’s head of global technology applied research.

Importantly, this certification is something a classical computer can do. The way this works is that the client samples a subset of the bit strings in the readouts and performs a test called cross-entropy benchmarking. This test measures the probability that the numbers could have come from a non-quantum source. If the client is satisfied with this measurement, they can trust that the samples were genuinely the result of random circuit sampling. Otherwise, they may conclude that the data could have been generated by “spoofing” – that is, using a classical algorithm to mimic a quantum computer. The degree of confidence in this test, and the number of bits they are willing to settle for to achieve this confidence, is up to the client.

High-fidelity quantum computing

In the new work, Pistoia, Aaronson, Hung and colleagues sent challenge circuits to the 56-qubit Quantinuum H2-1 quantum computer over the Internet. The attraction of the Quantinuum H2-1, Pistoia explains, is its high fidelity: “Somebody could say ‘Well, when it comes to randomness, why would you care about accuracy – it’s random anyway’,” he says. “But we want to measure whether the number that we get from Quantinuum really came from a quantum computer, and a low-fidelity quantum computer makes it more difficult to ascertain that with confidence… That’s why we needed to wait all these years, because a low-fidelity quantum computer wouldn’t have given us the certification part.”

The team then certified the randomness of the bits they got back by performing cross-entropy benchmarking using four of the world’s most powerful supercomputers, including Frontier at the US Department of Energy’s Oak Ridge National Laboratory. The results showed that it would have been impossible for a dishonest adversary with similar classical computing power to spoof a quantum computer – provided the client set a short enough time limit.

One drawback is that at present, the computational cost of verifying that random numbers have not been spoofed is similar to the computational cost of spoofing them. “New work is needed to develop approaches for which the certification process can run on a regular computer,” Pistoia says. “I think this will remain an active area of research in the future.”

Studying other problems

Quantinuum has also released the results of two scientific studies performed using the Quantinuum H2-1. The first examines a well-known problem in knot theory involving the Jones polynomial. The second explores quantum magnetism, which was also the subject of quantum computing work by groups at Harvard University, Google Quantum AI and, most recently, D-Wave Systems. Michael Foss-Feig, a quantum computing theorist at Quantinuum who led the quantum magnetism study, explains that the groups focused on different problems, with Quantinuum and its American and European academic collaborators studying thermalization rather than quantum phase transitions.

A more important difference, Foss-Feig argues, is that whereas the other groups used a partly analogue approach to simulating their quantum magnetic system, with all quantum gates activated simultaneously, Quantinuum’s approach divided time into a series of discrete steps, with operations following in a sequence similar to that of a classical computer. This digitization meant the researchers could perform a discrete gate operation as required, between any of the ionic qubits in their lattice. “This digital architecture is an extremely convenient way to compile a very wide range of physical problems,” Foss-Feig says. “You might think, for example, of simulating not just spins, for example, but also fermions or bosons.”

While the researchers say it would be just possible to reproduce these simulations using classical computers, they plan to study larger models soon. A 96-qubit version of their device, called Helios, is slated for launch later in 2025.

“We’ve gone through a shift”

Quantum information scientist Barry Sanders of the University of Calgary, Canada is impressed by all three works. “The real game changer here is Quantinuum’s really nice 56-qubit quantum computer,” he says. “Instead of just being bigger in its number of qubits, it’s hit multiple important targets.”

In Sanders’ view, the computer’s fully digital architecture is important for scalability, although he notes that many in the field would dispute that. The most important development, he adds, is that the research frames the value of a quantum computer in terms of its accomplishments.

“We’ve gone through a shift: when you buy a normal computer, you want to know what that computer can do for you, not how good is the transistor,” he says. “In the old days, we used to say ‘I made a quantum computer and my components are better than your components – my two-qubit gate is better’… Now we say, ‘I made a quantum computer and I’m going to brag about the problem I solved’.”

The random number generation paper is published in Nature. The others are available on the arXiv pre-print server.

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A team of researchers in Switzerland, Germany and the US has observed clear evidence of quantum mechanical interference behaviour in collisions between a methane molecule and a gold surface. As well as extending the boundaries of quantum effects further into the classical world, the team say the work has implications for surface chemistry, which is important for many industrial processes.

The effects of interference in light are generally easy to observe. Whenever a beam of light passes through closely-spaced slits or bounces off an etched grating, an alternating pattern of bright and dark intensity modulations appears, corresponding to locations of constructive and destructive interference, respectively. This was the outcome of Thomas Young’s original double-slit experiment, which was carried out in the 1800s and showed that light behaves like a wave.

For molecules and other massive objects, observing interference is trickier. Though quantum mechanics decrees that these also interfere when they scatter off surfaces, and a 1920s version of Young’s double-slit experiment showed that this was true for electrons, the larger the objects are, the more difficult it is to observe interference effects. Indeed, the disappearance of such effects is a sign that the object’s wavefunction has “decohered” – that is, the object has stopped behaving like a wave and started obeying the laws of classical physics.

Similar to the double-slit experiment

In the new work, researchers led by Rainer Beck of the EPFL developed a way to observe interference in complex polyatomic molecules. They did this by using an infrared laser to push methane (CH₄) molecules into specific rovibrational states before scattering the molecules off an atomically smooth and chemically inert Au(111) surface. They then detected the molecules’ final states using a second laser and an instrument called a bolometer that measures the tiny temperature change as molecules absorb the laser’s energy.

Using this technique, Beck and colleagues identified a pattern in the quantum states of the methane molecules after they collided with the surface. When two states had different symmetries, the quantum mechanical amplitudes for the different pathways taken during the transition between them cancelled out. In states with the same symmetry, however, the pathways reinforced each other, leading to an intense, clearly visible signal.

The researchers say that this effect is similar to the destructive and constructive interference of the double-slit experiment, but not quite the same. The difference is that interference in the double-slit experiment stems from diffraction, whereas the phenomenon Beck and colleagues observed relates to the rotational and vibrational states of the methane molecules.

A rule to explain the patterns

The researchers had seen hints of such behaviour in experiments a few years ago, when they scattered methane from a nickel surface. “We saw that some rotational quantum states were somewhat weakly populated by the collisions while other states that were superficially very similar (that is, with the same energy and same angular momentum) were more strongly populated,” explains Christopher Reilly, a postdoctoral researcher at EPFL and the lead author of a paper in Science on the work. “When we moved on to collisions with a gold surface, we discovered that these population imbalances were now very pronounced.”

This discovery spurred them to find an explanation. “We concluded that we might be observing a conservation of the reflection parity of the methane molecule’s wavefunction,” Reilly says. “We then set out to test it for molecules prepared in vibrationally excited states and our results confirmed our hypothesis spectacularly.”

Because the team’s technique for detecting quantum states relies on spectroscopy, Reilly says the “intimidating complexity” of the spectrum of quantum states in a medium-sized molecule like methane was a challenge. “While our narrow-bandwidth lasers allowed us to probe the population in individual quantum states, we still needed to know exactly which wavelength we need to tune the laser wavelength to in order to address a given state,” he explains.

This, in turn, meant knowing the molecule’s energy levels very precisely, as they were trying to compare populations of states with only marginally different energies. “It is only just in the last couple years that modelling of methane’s spectrum has become accurate enough to permit a reliable assignment of the quantum states involved in a given infrared transition,” Reilly says, adding that the HITEMP project of the HITRAN spectroscopic database was a big help.

Rethinking molecule-surface dynamics

According to Reilly, the team’s results show that classical models cannot fully capture molecule-surface dynamics. “This has implications for our general understanding of chemistry at surfaces, which is where in fact the majority of chemistry relevant to industry (think catalysts) and technology (think semiconductors) occurs,” he says. “The first step of any surface reaction is the adsorption of the reactants onto the surface and this step often requires the overcoming of some energetic barrier. Whether an incoming molecule will adsorb depends not only on the molecule’s total energy but on whether this energy can be effectively channelled into overcoming the barrier.

“Our scattering experiments directly probe these dynamics and show that, to really understand the different fundamental steps of surface chemistry, quantum mechanics is needed,” he tells Physics World.

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Physicists at the Georgia Institute of Technology, US have introduced a novel way to generate entanglement between photons – an essential step in building scalable quantum computers that use photons as quantum bits (qubits). Their research, published in Physical Review Letters, leverages a mathematical concept called non-Abelian quantum holonomy to entangle photons in a deterministic way without relying on strong nonlinear interactions or irrevocably probabilistic quantum measurements.

Entanglement is fundamental to quantum information science, distinguishing quantum mechanics from classical theories and serving as a pivotal resource for quantum technologies. Existing methods for entangling photons often suffer from inefficiencies, however, requiring additional particles such as atoms or quantum dots and additional steps such as post-selection that eliminate all outcomes of a quantum measurement in which a desired event does not occur.

While post-selection is a common strategy for entangling non-interacting quantum particles, protocols for entangled state preparation that use post-selection are non-deterministic. This is because they rely upon making measurements, and the result of obtaining a certain state of the system after a measurement is associated with a probability, making it inevitably non-deterministic.

Non-Abelian holonomy

The new approach provides a direct and deterministic alternative. In it, the entangled photons occupy distinguishable spatial modes of optical waveguides, making entanglement more practical for real-world applications. To develop it, Georgia Tech’s Aniruddha Bhattacharya and Chandra Raman took inspiration from a 2023 experiment by physicists at Universität Rostock, Germany, that involved coupled photonic waveguides on a fused silica chip. Both works exploit a property known as non-Abelian holonomy, which is essentially a geometric effect that occurs when a quantum system evolves along a closed path in parameter space (more precisely, it is a matrix-valued generalization of a pure geometric phase).

In Bhattacharya and Raman’s approach, photons evolve in a waveguide system where their quantum states undergo a controlled transformation that leads to entanglement. The pair derive an analytical expression for the holonomic transformation matrix, showing that the entangling operation corresponds to a unitary rotation within an effective pseudo-angular momentum space. Because this process is fully unitary, it does not require measurement or external interventions, making it inherently robust.

Beyond the Hong-Ou-Mandel effect

A classic example of photon entanglement is the Hong–Ou–Mandel (HOM) effect, where two identical photons interfere at a beam splitter, leading to quantum correlations between them. The new method extends such interference effects beyond two photons, allowing deterministic entanglement of multiple photons and even higher-dimensional quantum states known as qudits (d-level systems) instead of qubits (two-level systems). This could significantly improve the efficiency of quantum information protocols.

Because state preparation and measurement are relatively straightforward in this approach, Bhattacharya and Raman say it is well-suited for quantum computing. Since the method relies on geometric principles, it naturally protects against certain types of noise, making it more robust than traditional approaches. They add that their technique could even be used to construct an almost universal set of near-deterministic entangling gates for quantum computation with light. “This innovative use of non-Abelian holonomy could shift the way we think about photonic quantum computing,” they say.

By providing a deterministic and scalable entanglement mechanism, Bhattacharya and Raman add that their method opens the door to more efficient and reliable photonic quantum technologies. The next steps will be to validate the approach experimentally and explore practical implementations in quantum communication and computation. Further in the future, it will be necessary to find ways of integrating this approach with other quantum systems, such as matter-based qubits, to enable large-scale quantum networks.

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Water molecules on the surface of an electrode flip just before they give up electrons to form oxygen – a feat of nanoscale gymnastics that explains why the reaction takes more energy than it theoretically should. After observing this flipping in individual water molecules for the first time, scientists at Northwestern University in the US say that the next step is to find ways of controlling it. Doing so could improve the efficiency of the reaction, making it easier to produce both oxygen and hydrogen fuel from water.

The water splitting process takes place in an electrochemical cell containing water and a metallic electrode. When a voltage is applied to the electrode, the water splits into oxygen and hydrogen via two separate half-reactions.

The problem is that the half-reaction that produces oxygen, known as the oxygen evolution reaction (OER), is difficult and inefficient and takes more energy than predicted by theory. “It should require 1.23 V,” says Franz Geiger, the Northwestern physical chemist who led the new study, “but in reality, it requires more like 1.5 or 1.8 V.” This extra energy cost is one of the reasons why water splitting has not been implemented on a large scale, he explains.

Determining how water molecules arrange themselves

In the new work, Geiger and colleagues wanted to test whether the orientation of the water’s oxygen atoms affects the kinetics of the OER. To do this, they directed an 80-femtosecond pulse of infrared (1034 nm) laser light onto the surface of the electrode, which was in this case made of nickel. They then measured the intensity of the reflected light at half the incident wavelength.

This method, which is known as second harmonic and vibrational sum-frequency generation spectroscopy, revealed that the water molecules’ alignment on the surface of the electrode depended on the applied voltage. By analysing the amplitude and phase of the signal photons as this voltage was cycled, the researchers were able to pin down how the water molecules arranged themselves.

They found that before the voltage was applied, the water molecules were randomly oriented. At a specific applied voltage, however, they began to reorient. “We also detected water dipole flipping just before cleavage and electron transfer,” Geiger adds. “This allowed us to distinguish flipping from subsequent reaction steps.”

An unexplored idea

The researchers’ explanation for this flipping is that at high pH levels, the surface of the electrode is negatively charged due to the presence of nickel hydroxide groups that have lost their protons. The water molecules therefore align with their most positively charged ends facing the electrode. However, this means that the ends containing the electrons needed for the OER (which reside in the oxygen atoms) are pointing away from the electrode. “We hypothesized that water molecules must flip to align their oxygen atoms with electrochemically active nickel oxo species at high applied potential,” Geiger says.

This idea had not been explored until now, he says, because water absorbs strongly in the infrared range, making it appear opaque at the relevant frequencies. The electrodes typically employed are also too thick for infrared light to pass through. “We overcame these challenges by making the electrode thin enough for near-infrared transmission and by using wavelengths where water’s absorbance is low (the so-called ‘water window’),” he says.

Other challenges for the team included designing a spectrometer that could measure the second harmonic generation amplitude and phase and developing an optical model to extract the number of net-aligned water molecules and their flipping energy. “The full process – from concept to publication – took three years,” Geiger tells Physics World.

The team’s findings, which are detailed in Science Advances, suggest that controlling the orientation of water at the interface with the electrode could improve OER catalyst performance. For example, surfaces engineered to pre-align water molecules might lower the kinetic barriers to water splitting. “The results could also refine electrochemical models by incorporating structural water energetics,” Geiger says. “And beyond the OER, water alignment may also influence other reactions such as the hydrogen evolution reaction and CO₂ reduction to liquid fuels, potentially impacting multiple energy-related technologies.”

The researchers are now exploring alternative electrode materials, including NiFe and multi-element catalysts. Some of the latter can outperform iridium, which has traditionally been the best-performing electrocatalyst, but is very rare (it comes from meteorites) and therefore expensive. “We have also shown in a related publication (in press) that water flipping occurs on an earth-abundant semiconductor, suggesting broader applicability beyond metals,” Geiger reveals.

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Complex hydrogel structures created using 3D printing are increasingly employed in fields including flexible electronics, soft robotics and regenerative medicine. Currently, however, such hydrogels are often soft and fragile, limiting their practical utility. Researchers at Zhejiang University in China have now fabricated 3D-printed hydrogels that can be easily, and repeatably, switched between soft and hard states, enabling novel applications such as smart medical bandages or information encryption.

“Our primary motivation was to overcome the inherent limitations of 3D-printed hydrogels, particularly their soft, weak and fragile mechanical properties, to broaden their application potential,” says co-senior author Yong He.

The research team created the hard/soft switchable composite by infusing supersaturated salt solution (sodium acetate, NAAC) into 3D-printed polyacrylamide (PAAM)-based hydrogel structures. The hardness switching is enabled by the liquid/solid transition of the salt solution within the hydrogel.

Initially, the salt molecules are arranged randomly within the hydrogel and the PAAM/NAAC composite is soft and flexible. The energy barrier separating the soft and hard states prevents spontaneous crystallization, but can be overcome by artificially seeding a crystal nucleus (via exposure to a salt crystal or contact with a sharp object). This seed promotes a phase transition to a hard state, with numerous rigid, rod-like nanoscale crystals forming within the hydrogel matrix.

Superior mechanical parameters

The researchers created a series of PAAM/NAAC structures, using projection-based 3D printing to print hydrogel shapes and then soaking them in NAAC solution. Upon seeding, the structures rapidly transformed from transparent to opaque as the crystallization spread through the sample at speeds of up to 4.5 mm/s.

The crystallization dramatically changed the material’s mechanical performance. For example, a soft cylinder of PAAM/1.5NAAC (containing 150 wt% salt) could be easily compressed by hand, returning to its original shape after release. After crystallization, four 9x9x12 mm cylinders could support an adult’s weight without deforming.

For this composite, just 1 min of crystallization dramatically increased the compression Young’s modulus compared with the soft state. And after 24 h, the Young’s modulus grew from 110 kPa to 871.88 MPa. Importantly, the hydrogel could be easily returned to its soft state by heating and then cooling, a process that could be repeated many times.

The team also performed Shore hardness testing on various composites, observing that hardness values increased with increasing NAAC concentration. In PAAM/1.7NAAC composites (170 wt% salt), the Shore D value reached 86.5, comparable to that of hard plastic materials.

The hydrogel’s crosslinking density also impacted its mechanical performance. For PAAM/1.5NAAC composites, increasing the mass percentage of polymer crosslinker from 0.02 to 0.16 wt% increased the compression Young’s modulus to 1.2 GPa and the compression strength to 81.7 MPa. The team note that these parameters far exceed those of any existing 3D-printed hydrogels.

Smart plaster cast

He and colleagues demonstrated how the hard/soft switching and robust mechanical properties of PAAM/NAAC can create medical fixation devices, such as a smart plaster cast. The idea here is that the soft hydrogel can be moulded around the injured bone, and then rapidly frozen in shape by crystallization to support the injury and promote healing.

The researchers tested the smart plaster cast on an injured forearm. After applying a layer of soft cotton padding, they carefully wrapped around layers of the smart plaster bandage (packed within a polyethylene film to prevent accidental seeding). The flexible hydrogel could be conformed to the curved surface of limbs and then induced to crystallize.

After just 10 min of crystallization, the smart plaster cast reached a yield strength of 8.7 MPa, rapidly providing support for the injured arm. In comparison, a traditional plaster cast (as currently used to treat bone fractures) took about 24 h to fully harden, reaching a maximum yield strength of 3.9 MPa

To determine the safety of the exothermic crystallization process, the team monitored temperature changes in the plaster cast nearest to the skin. The temperature peaked at 41.5 °C after 25 min of crystallization, below the ISO-recommended maximum safe temperature of 50 °C.

The researchers suggest that the ease of use, portability and fast response of the smart plaster cast could provide a simple and effective solution for emergency and first aid situations. Another benefit is that, in contrast to traditional plaster casts that obstruct X-rays and hinder imaging, X-rays easily penetrate through the smart plaster cast to enable high-quality imaging during the healing process.

While the composites exhibit high strength and Young’s modulus, they are not as tough as ideally desired. “For example, the elongation at break was less than 10% in tensile testing for the PAAM/1.5NAAC and PAAM/1.7NAAC samples, highlighting the challenge of balancing toughness with strength and modulus,” He tells Physics World. “Therefore, our current research focuses on enhancing the toughness of these composite materials without compromising their modulus, with the goal of developing strong, tough and mechanically switchable materials.”

The hydrogel is described in the International Journal of Extreme Manufacturing.

The post Hydrogels rapidly switch from soft to hard to create smart medical bandage appeared first on Physics World.

In 2014 the American mathematical physicist S James Gates Jr shared his “theorist’s bucket list” of physics discoveries he would like to see happen before, as he puts it, he “shuffles off this mortal coil”. A decade later, Physics World’s Margaret Harris caught up once more with Gates, who is now at the University of Maryland, US, to see what discoveries he can check off his list; what he would still like to see discovered, proven or explored; and what more he might add to the list, as of 2025.

The first thing on your list 10 years ago was the discovery of the Higgs boson, which had happened. The next thing on your list was gravitational waves.

The initial successful detection of gravity waves [in 2015] was a spectacular day for a lot of us. I had been following the development of that detector [the Laser Interferometer Gravitational-wave Observatory, or LIGO] almost from its birth. The first time I heard about detecting gravity waves was around 1985. I was a new associate professor at Maryland, and a gentleman by the name of [Richard] Rick Isaacson, who was a programme officer at the National Science Foundation (NSF), called me one day into his office to show me a proposal from a Caltech-MIT collaboration to fund a detector. I read it and I said this will never work. Fortunately, Isaacson is a superhero and made this happen because for decades he was the person in the NSF with the faith that this could happen; so when it did, it was just an amazing day.

Why is the discovery of these gravitational waves so exciting for physicists?

Albert Einstein’s final big prediction was that there would be observable gravitational waves in the universe. It’s very funny – if you go back into the literature, he first says yes this is possible, but at some point he changes his mind again. It’s very interesting to think about how human it is to bounce back and forth, and then to have Mother Nature say look, you got it right the first time. So such a sharp confirmation of the theory of general relativity was unlike anything I could imagine happening in my lifetime, quite frankly, even though it was on my bucket list.

The other thing is that our species knows about the heavens mostly because there have been “entities” that are similar to Mercury, the Greek god who carried messages from Mount Olympus. In our version of the story, Mercury is replaced by photons. It’s light that has been telling us for hundreds of thousands of years, maybe a million years, that there’s something out there and this drove the development of science for several hundred years. With the detection of gravitational waves, there’s a new kid on the block to deliver the message, and that’s the graviton. Just like light, it has both particle and wave aspects, so now we have detected gravitational waves, the next big thing is to be able to detect gravitons.

We are not completely clear on exactly how to see gravitons, but once we have that knowledge, we will be able to do something that we’ve never been able to do as a species in this universe. After the initial moments of the Big Bang, there was a period of darkness, when matter was far too hot to form neutral atoms, and light could not travel through the dense plasma. It took 380,000 years for electrons to be trapped in orbits around nuclei, forming the first atoms.

Eventually, the universe had expanded so much that the average temperature and density of particles had dropped enough for light to travel. Now what’s really interesting is if you look at the universe via photons, you can only look so far back up to that point when light was first able to travel through the universe, often referred to as the “first dawn”. We detected this light in the 1960s, and it’s called the cosmic microwave background. If you want to peer further back in time beyond this period, you can’t use light but you can use gravitational waves. We will be able as a species eventually to look maybe all the way back to the Big Bang, and that’s remarkable.

What’s the path to seeing gravitons experimentally?

At the time that gravitational waves were detected by LIGO there were three different detectors, two in the US and one on the border of France and Italy called Virgo. There is a new LIGO site coming online in India now, and so what’s going to happen, provided there continues to be a global consensus on continuing to do this science, is that more sites like this are going to come online, which will give us higher-fidelity pictures. It’s going to be a difference akin to going from black and white TV to colour.

In the universe now, the pathway to detecting gravitons involves two steps. First, you probably want to measure the polarization of gravitons, and Fabry–Pérot interferometers, such as LIGO, have that capacity. If it’s a polarized graviton wave, the bending of space-time has a certain signature, whether it’s left or right-handed. If we are lucky enough we will actually see that polarization, I would guess within the next 10 years.

The second step is quantization, which is going to be a challenge. Back in the 1960s a physicist at the University of Maryland named Joseph Weber developed what are now called Weber bars. They’re big metal bars and the idea was you cool them down and then if a graviton impinges on these bars, it would induce lattice vibrations in the metal, and you would detect those. I suspect there’s going to be a big push in going back and upgrading that technology. One of the most exciting things about that is they might be quantum Weber bars. That’s the road that I could see to actually nailing down the existence of the graviton.

Number three on your bucket list from a decade ago was supersymmetry. How have its prospects developed in the past 10 years?

At the end of the Second World War, in an address to the Japanese people after the atomic bombing of Hiroshima and Nagasaki, the Japanese emperor [known as Showa in Japan, Hirohito in the West] used the phrase “The situation has developed not necessarily to our advantage”, and I believe we can apply that to supersymmetry. In 2006 I published a paper where I said explicitly I did not expect the Large Hadron Collider (LHC) to detect supersymmetry. It was a back-of-the-envelope calculation, where I was looking at the issue of anomalous magnetic moments. Because the magnetic moments can be sensitive to particles you can’t actually detect, by looking at the anomalous magnetic moment and then comparing the measured value to what is predicted by all the particles that you know, you can put lower bounds on the particles that you don’t know, and that’s what I did to come up with this number.

It looked to me like the lightest “superpartner” was probably going to be in the range of 30 Tev. The LHC’s initial operations were at 7 TeV and it’s currently at 14 TeV, so I’m feeling comfortable about this issue. If it’s not found by the time we reach 100 Tev, well, I’m likely going to kick the bucket by the time we get that technology. But I am confident that SUSY is out there in nature for reasons of quantum stability.

Also, observations of particle physics – particularly high-precision observations, magnetic moments, branching ratios, decay rates – are not the only way to think about finding supersymmetry. In particular, one could imagine that within string theory, there might be cosmological implications (arXiv:1907.05829), which are mostly limited to the question of dark matter and dark energy. When it comes to the dark-matter contribution in the universe, if you look at the mathematics of supersymmetry, you can easily find that there are particles that we haven’t observed yet and these might be the lightest supersymmetric particle.

And the final thing in your bucket list, which you’ve touched on, was superstring theory. When we last spoke, you said that you did not expect to see it. How has that changed, if at all?

Unless I’m blessed with a life as long as Methuselah, I don’t expect to see that. I think that for superstring theory to win observational acceptance, it will likely come about not from a single experiment, but from a confluence of observations of the cosmology and astrophysics type, and maybe then the lightest super symmetric particle will be found. By the way, I don’t expect extra dimensions ever to be found. But if I did have several hundred years to live, those are the kinds of likely expectations I would have.

And have you added anything new to your bucket list over the past 10 years?

Yes, but I don’t quite know how to verbalize it. It has to do with a confluence of things around quantum mechanics and information. In my own research, one of the striking things about the graphs that we developed to understand the representation theory of supersymmetry –we call them “adinkras” – is that error-correcting codes are part of these constructs. In fact, for me this is the proudest piece of research I’ve ever enabled – to discover a kind of physics law, or at least the possibility of a physics law, that includes error-correcting codes. I know of no previous example in history where a law of physics includes error-correcting codes, but we can clearly see it in the mathematics around these graphs (arXiv:1108.4124).

That had a profound impact on the way I think about information theory. In the 1980s, John Wheeler came up with this very interesting way to think about quantum mechanics (“Information, physics, quantum: the search for links” Proc. 3rd Int. Symp. Foundations of Quantum Mechanics, Tokyo, 1989, pp354–368). A shorthand phrase to describe it is “it from bit” – meaning that the information that we see in the universe is somehow connected to bits. As a young person, I thought that was the craziest thing I had ever heard. But in my own research I saw that it’s possible for the laws of physics to contain bits in the form of error-correcting codes, so I had to then rethink my rejection of what I thought was a wild idea.

In fact, now that I’m old, I’ve concluded that if you do theoretical physics long enough, you too can become crazy – because that’s what sort of happened to me! In the mathematics of supersymmetry, there is no way to avoid the presence of error-correcting codes and therefore bits. And because of that my new item for the bucket list is an actual observational demonstration that the laws of quantum mechanics entail the use of information in bits.

In terms of when we might see that, it will be long after I’ve gone. Unless I somehow get another 150 years of life. Intellectually, that’s how long I would estimate it will take as of now, because the hints are so stark, they suggest something is definitely going on.

We’ve talked a little bit about how science has changed in the past 10 years. Of course, science is not unconnected with the rest of the world. There have been some changes in other things that impinge on science, particularly those recently developing in the US. What’s your take on that?

Unfortunately, it’s been very predictable. Two years ago I wrote an essay called “Expelled from the mountain top?” (Science 380 993). I took that title from a statement by Martin Luther King Jr where he says “I’ve been to the mountaintop”, and the part about being “expelled” refers to closing down opportunities for people of colour. In my essay I talked about the fact that it looked to me like the US was moving in a direction where it would be less likely that people like me – a man of colour, an African American, a scientist – would continue to have access to the kind of educational training that it takes to do this [science].

I’m still of the opinion that the 2023 decision the Supreme Court made [about affirmative action] doesn’t make sense. What it is saying is that diversity has no role in driving innovation. But there’s lots of evidence that that’s not right. How do you think cities came into existence? They are places where innovation occurs because you have diverse people coming to cities.

You add to that the presence of a new medium – the Internet – and the fact that with this new medium, anyone can reach millions of people. Why is this a little bit frightening? Well, fake news. Misinformation.

I ran into a philosopher about a year ago, and he made a statement that I found very profound. He said think of the printing press. It allowed books to disseminate through Western European society in a way that had never happened before, and therefore it drove literacy. How long did it take for literacy levels to increase? 50 to 100 years. Then he said, now let’s think about the Internet. What’s different about it? The difference is that anyone can say anything and reach millions of people. And so the challenge is how long it will take for our species to learn to write the Internet without misinformation or fake news. And if he’s right, that’s 100, 150 years. That’s part of the challenge that the US is facing. It’s not just a challenge for my country, but somehow it seems to be particularly critical in my country.

So what does this have to do with science? In 2005 I was invited to deliver a plenary address to the American Association for the Advancement of Science annual meeting. In that address, I made statements about science being turned off because it was clear to me, even back then in my country, that there were elements in our society that would be perfectly happy to deny evidence brought forth by scientists, and that these elements were becoming stronger.

You put this all together and it’s going to be an extraordinarily important, challenging time for the continuation of science because, certainly at the level of fundamental science, this is something that the public generally has to say “Yes, we want to invest in this”. If you have agencies and agents in society denying vaccines, for example, or denying the scientific evidence around evolution or climate change, if this is going to be something that the public buys into, then science itself potentially can be turned off, and that’s the thing I was warning about in 2005.

What are some practical things that members of the scientific community can do to help prevent that from happening?

First of all, come down from the ivory tower. I’ve been a part of some activities, and they normally are under the rubric of restoring the public’s trust in science, and I think that’s the wrong framing. It’s the public faith in science that’s under attack. So from my perspective, that’s what I’d much rather have people really thinking about.

What would you say the difference is between having trust in science and having faith in science?

In my mind, if I trust something, I will listen. If I have faith in something, I will listen and I will act. To me, this is a sharp distinction.

Personally, even though I expect that it’s going to be really hard going forward, I am hopeful. And I would urge young people never to lose that hope. If you lose hope, there is no hope. It’s just that simple. And so I am hopeful. Even though people may take my comments as “oh, he’s just depressed” – no, I’m not. Because I’m a scientist, I believe that one must, in a clear-eyed, hard-headed manner, look at the evidence that’s in front of us and not sentimentally try to dodge what you see, and that’s who I am. So I am hopeful in spite of all the things that I’ve just said to you.

The post A theoretical physicist’s bucket list, 10 years later: Jim Gates on the graviton, quantum information and the scientific climate in the US appeared first on Physics World.

If a water droplet flowing over a surface gets stuck, and then unsticks itself, it generates an electric charge. The discoverers of this so-called depinning phenomenon are researchers at RMIT University and the University of Melbourne, both in Australia, and they say that boosting it could make energy-harvesting devices more efficient.

The newly observed charging mechanism is conceptually similar to slide electrification, which occurs when a liquid leaves a surface – that is, when the surface goes from wet to dry. However, the idea that the opposite process can also generate a charge is new, says Peter Sherrell, who co-led the study. “We have found that going from dry to wet matters as well and may even be (in some cases) more important,” says Sherrell, an interdisciplinary research fellow at RMIT. “Our results show how something as simple as water moving on a surface still shows basic phenomena that have not been understood yet.”

Co-team leader Joe Berry, a fluid dynamics expert at Melbourne, notes that the charging mechanism only occurs when the water droplet gets temporarily stuck on the surface. “This suggests that we could design surfaces with specific structure and/or chemistry to control this charging,” he says. “We could reduce this charge for applications where it is a problem – for example in fuel handling – or, conversely, enhance it for applications where it is a benefit. These include increasing the speed of chemical reactions on catalyst surfaces to make next-generation batteries more efficient.”

More than 500 experiments

To observe depinning, the researchers built an experimental apparatus that enabled them to control the sticking and slipping motion of a water droplet on a Teflon surface while measuring the corresponding change in electrical charge. They also controlled the size of the droplet, making it big enough to wet the surface all at once, or smaller to de-wet it. This allowed them to distinguish between multiple mechanisms at play as they sequentially wetted and dried the same region of the surface.

Their study, which is published in Physical Review Letters, is based on more than 500 wetting and de-wetting experiments performed by PhD student Shuaijia Chen, Sherrell says. These experiments showed that the largest change in charge – from 0 to 4.1 nanocoulombs (nC) – occurred the first time the water contacted the surface. The amount of charge then oscillated between about 3.2 and 4.1 nC as the system alternated between wet and dry phases. “Importantly, this charge does not disappear,” Sherrell says. “It is likely generated at the interface and probably retained in the droplet as it moves over the surface.”

The motivation for the experiment came when Berry asked Sherrell a deceptively simple question: was it possible to harvest electricity from raindrops? To find out, they decided to supervise a semester-long research project for a master’s student in the chemical engineering degree programme at Melbourne. “The project grew from there, first with two more research project students [before] Chen then took over to build the final experimental platform and take the measurements,” Berry recalls.

The main challenge, he adds, was that they did not initially understand the phenomenon they were measuring. “Another obstacle was to design the exact protocol required to repeatedly produce the charging effect we observed,” he says.

Potential applications

Understanding how and why electric charge is generated as liquids flow during over surfaces is important, Berry says, especially with new, flammable types of renewable fuels such as hydrogen and ammonia seen as part of the transition to net zero. “At present, with existing fuels, charge build-up is reduced by restricting flow using additives or other measures, which may not be effective in newer fuels,” he explains. “This knowledge may help us to engineer coatings that could mitigate charge in new fuels.”

The RMIT/Melbourne researchers now plan to investigate the stick-slip phenomenon with other types of liquids and surfaces and are keen to partner with industries to target applications that can make a real-world impact. “At this stage, we have simply reported that this phenomenon occurs,” Sherrell says. “We now want to show that we can control when and where these charging events happen – either to maximize them or eliminate them. We are still a long way off from using our discovery for chemical and energy applications – but it’s a big step in the right direction.”

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An international team led by chemists at the University of British Columbia (UBC), Canada, has reported strong experimental evidence for a superfluid phase in molecular hydrogen at 0.4 K. This phase, theoretically predicted in 1972, had only been observed in helium and ultracold atomic gases until now, and never in molecules. The work could give scientists a better understanding of quantum phase transitions and collective phenomena. More speculatively, it could advance the field of hydrogen storage and transportation.

Superfluidity is a quantum mechanical effect that occurs at temperatures near absolute zero. As the temperatures of certain fluids approach this value, they undergo a transition to a zero-viscosity state and begin to flow without resistance – behaviour that is fundamentally different to that of ordinary liquids.

Previously, superfluidity had been observed in helium (³He and ⁴He) and in clusters of ultracold atoms known as Bose-Einstein condensates. In principle, molecular hydrogen (H₂), which is the simplest and lightest of all molecules, should also become superfluid at ultracold temperatures. Like ⁴He, H₂ is a boson, so it is theoretically capable of condensing into a superfluid phase. The problem is that it is only predicted to enter this superfluid state at a temperature between 1 and 2 K, which is lower than its freezing point of 13.8 K.

A new twist on a spinning experiment

To keep their molecular hydrogen liquid below its freezing point, team leader Takamasa Momose and colleagues at UBC confined small clusters of hydrogen molecules inside helium nanodroplets at 0.4 K. They then embedded a methane molecule in the hydrogen cluster and observed its rotation with laser spectroscopy.

Momose describes this set-up as a miniature version of an experiment performed by the Georgian physicist Elephter Andronikashvili in 1946, which showed that disks inside superfluid helium could rotate without resistance. They chose methane as their “disk”, Momose explains, because it rotates quickly and interacts only very weakly with H₂, meaning it does not disturb the behaviour of the medium in which it spins.

Onset of superfluidity

In clusters containing less than six hydrogen molecules, they observed some evidence of friction affecting the methane’s rotation. As the clusters grew to 10 molecules, this friction began to disappear and the spinning methane molecule rotated faster, without resistance. This implies that most of the hydrogen molecules around it are behaving as a single quantum entity, which is a signature of superfluidity. “For clusters larger than N = 10, the hydrogen acted like a perfect superfluid, confirming that it flows with zero resistance,” Momose tells Physics World.

The researchers, who have been working on this project for nearly 20 years, say they took it on because detecting superfluidity in H₂ is “one of the most intriguing unanswered questions in physics – debated for 50 years”. As well as working out how to keep hydrogen in a liquid state at extremely low temperatures, they also had to find a way to detect the onset of superfluidity with high enough precision. “By using methane as a probe, we were finally able to measure how hydrogen affects its motion,” Momose says.

A deeper understanding

The team say the discovery opens new avenues for exploring quantum fluids beyond helium. This could lead scientists to a deeper understanding of quantum phase transitions and collective quantum phenomena, Momose adds.

The researchers now plan to study larger hydrogen clusters (ranging from N = 20 to over a million) to understand how superfluidity evolves with size and whether the clusters eventually freeze or remain fluid. “This will help us explore the boundary between quantum and classical matter,” Momose explains.

They also want to test how superfluid hydrogen responds to external stimuli such as electric and magnetic fields. Such experiments could reveal even more fascinating quantum behaviours and deepen our understanding of molecular superfluidity, Momose says. They could also have practical applications, he adds.

“From a practical standpoint, hydrogen is a crucial element in clean energy technologies, and understanding its quantum properties could inspire new approaches for hydrogen storage and transportation,” he says. “The results from these [experiments] may also provide critical insights into achieving superfluidity in bulk liquid hydrogen – an essential step toward harnessing frictionless flow for more efficient energy transport systems.”

The researchers report their work in Science Advances.

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I recently met an old friend from the time when we both worked in the light-emitting diode (LED) industry. We started discussing how every technology has its day – a window of opportunity – but also how hard it is to know which companies will succeed long-term. As we got talking, I was reminded of a very painful product launch by an LED lighting firm that I was running at the time.

The incident occurred in 2014 when my company had a technology division that was developing wirelessly connected lighting. Our plan was to unveil our new Bluetooth control system at a trade show, but everything that could go wrong for us on the day pretty much did. However, the problems with our product weren’t down to any
particular flaws in our technology.

Instead, they were triggered by issues with a technology from a rival lighting firm that was also exhibiting at the event. We ended up in a rather ugly confrontation with our competitors, who seemed in denial about their difficulties. I realized there was a fundamental problem with their technology – even if they couldn’t see it – and predicted that, for them, the writing was on the wall.

Bother at the booth

Our plan was to put microprocessors and radios into lighting to make it smart, more energy efficient and with integrated sensors and Bluetooth controls. There were no fundamental physics barriers – it just needed some simple thermal management (the LEDs and particularly the radios had to be kept below 70 ºC), some electronics and lots of software.

Back then, the LED lighting industry was following a technology roadmap that envisaged these solid-state devices eventually generating 320 lumens per watt, compared to about 10 lumens per watt from conventional incandescent lamps. As the road map progressed, there’d be ever fewer thermal challenges.

With more and more countries phasing out conventional bulbs, LEDs are continuing their march along the roadmap. Almost every bulb sold these days is an LED and the overall global lighting market was worth $140bn in 2023, according to Fortune Business Insights. Lighting accounts for 15–18% of all electricity consumption in the European Union alone.

Back at that 2014 trade show, called LuxLive, all initially seemed to be going well as we set up our display. There was the odd software bug, but were able to work around that and happily control our LED lights with a smart phone connected via WiFi to a low-cost lighting server (a bit like a Raspberry Pi), with the smart LED fixtures and sensors connected via Bluetooth.

With final preparations over, the trade show opened and our first customer came up to the stand. We started giving them a demo but nothing seemed to be working – to our surprise, we simply could not get our lights to respond. A flurry of behind-the-scenes activity ensured (mostly us switching everything off and on again) but nothing made a difference.

Strangely, my phone call appeared to go dead just as I passed another booth from a rival firm

To try to get to the bottom of things, I stepped a decent distance away from our booth and rang one of our technical team up in London for support. I explained our problem but, strangely, as I walked back towards the booth, I got cut off. My call appeared to have gone dead just as I passed another booth from a rival firm called Ceravision.

It was developing high-efficiency plasma (HEP) lamps that could generate up to 100 lumens per watt – roughly where LEDs were at the time. Its lamps used radio-frequency waves to heat a plasma without needing any electrodes. Designed for sports stadia and warehouses, Ceravision’s bulbs were super bright. In fact, I was almost blinded by its products, which were pointing into the aisle, presumably to attract attention.

Back at base, our technical team frantically tried to figure out why our products weren’t working. But they were stuck and I spent the rest of the day unable to demonstrate our products to potential customers. Then, as if by magic, our system started working again – just as someone noticed we weren’t being blinded by Ceravision’s light any more.

I walked over to Ceravision’s booth as its team was packing up and had a chat with a sales guy, who I asked how the system worked. He told me it was a microwave waveguide light source but didn’t appear to know much more. So I asked him if he wouldn’t mind turning on the light again to demonstrate its output, which he did.

I glanced back at my team, who a few moments earlier had been all smiles that our system was now working, even if they were confused as to why. Suddenly, as the Ceravision light was turned on, our system broke down again. I requested to speak to one of Ceravision’s technical team but was told they wouldn’t be back until the following day.

Lighting the way

I left for the show’s awards dinner, where my firm won an innovation award for the wireless lighting system we’d been trying – unsuccessfully – to demonstrate all day. Later that night, I started looking into Ceravision in more detail. Based in Milton Keynes, UK, its idea of an electrodeless lamp wasn’t new – Nikola Tesla had filed a patent for such a device back in 1894.

Tesla realized that this type of lamp would benefit from a long life and little discolouration as there are no electrodes to degrade or break. In fact, Tesla knew how to get around the bulbs’ technical drawbacks, which involved constraining the radio waves and minimizing their power. Eventually, in the late 1990s, as radio-frequency sources became available,  a US company called Fusion Lighting got this technology to market.

Its lamps consisted of a golf ball-sized fused-quartz bulb containing several milligrams of sulphur powder and argon gas at the end of a thin glass spindle. Enclosed in a microwave-resonant wire-mesh cage, the bulb was bombarded by 2.45 GHz microwaves from a magnetron of the kind you get in a microwave oven. The bulb had a design lifetime of about 60,000 hours and emitted 100 lumens per watt.

Unfortunately, its efficiency was poor as 80–85% of the light generated was trapped inside the opaque ceramic waveguide. Worse still, various satellite companies petitioned the US authorities to force Fusion Lighting to cut its electromagnetic emissions by 99.9%. They feared that otherwise its bulbs would interfere with WiFi, cordless phones and satellite radio services in North America, which also operate at 2.4 GHz.

In 2001 Fusion Lighting agreed to install a perforated metal shield around its lamps to reduce electromagnetic emissions by 95%. However, this decision only reduced the light output, making the bulbs even more inefficient. Ceravision’s solution was an optically clear quartz waveguide and integrated lamp that yielded 100–5000 watts of power without any damage to the lamps.

The company claimed its technology was ideal for growing plants – delivering blue and ultraviolet light missing from other sources – along with everything from sterilizing water to illuminating TV studios. And whereas most magnetrons break down after about 2000 hours, Ceravision’s magnetrons lasted for more than 40,000 hours. It had even signed an agreement with Toshiba to build high-efficient magnetrons.

What could possibly go wrong?

The truth hurts

Back at the trade show, I arrived the following morning determined to get a resolution with the Ceravision technical team. Casually, I asked one of them, who had turned up early, to come over to our booth to see our system. It was working – until the rest of Ceravision arrived and switched their lights on. Once again, our award-winning system gave up the ghost.

Ceravision refused to accept there was a correlation between their lights going on and our system breaking down

Things then got a little ugly. Ceravision staff refused to accept there was a correlation between their lights going on and our system breaking down. Our product must be rubbish, they said. If so, I asked, how come my mobile phone had stopped working too? Silence. I went to talk to the show organizers – all they could do was tell Ceravision to point its lights down, rather than into the aisle.

This actually worked for us as it seemed the “blocking signal” was reasonably directional. It became obvious from Ceravision’s defensive response that this WiFi blocking problem must have come up before – its staff had some over-elaborate and clearly rehearsed responses. As for us, we simply couldn’t show our product in its best light to customers, who just felt it wasn’t ready for market.

In the intervening years, I’ve talked to several ex-employees of Ceravision, who’ve all told me it trialled lots of different systems for different markets. But its products always proved to be too expensive and too complex – and eventually LEDs caught up with them. When I asked them about lights disrupting WiFi, most either didn’t seem aware of the issue or, if they did, knew it couldn’t be fixed without slashing the light output and efficiency of the bulbs.

That in turn forced Ceravision to look for ever more niche applications with ever-tinier markets. Many staff left, realizing the emperor had no clothes. Eventually, market forces took their toll on the company, which put its lighting business into receivership in 2020. Its parent company with all the patents and intellectual property suffered a similar fate in 2023.

I suspect (but don’t know for sure) that the window of opportunity closed due to high system costs, overly complex manufacturing and low volumes, coupled with LEDs becoming cheaper and more efficient. Looking back on 2014, the writing was really on the wall for the technology, even if no-one wanted to read the warning signs. A product that disrupts your mobile or WiFi signal was simply never going to succeed.

It was a classic case of a company having a small window of opportunity before better solutions came along and it missed the proverbial boat. Of course, hindsight is a wonderful thing. Clearly the staff could see what was wrong, but it took a long time for managers and investors to see or tackle the issues too. Perhaps when you are trying to deliver on promises you end up focusing on the wrong things.

The moral of the story is straightforward: constantly review your customers’ feedback and re-evaluate your products as the market develops. In business, it really is that simple if you want to succeed.

The post James McKenzie: how I knew the writing was on the wall for our rival’s lighting technology appeared first on Physics World.

A ground-breaking method to create “audible enclaves” – localized zones where sound is perceptible while remaining completely unheard outside – has been unveiled by researchers at Pennsylvania State University and Lawrence Livermore National Laboratory. Their innovation could transform personal audio experiences in public spaces and improve secure communications.

“One of the biggest challenges in sound engineering is delivering audio to specific listeners without disturbing others,” explains Penn State’s Jiaxin Zhong. “Traditional speakers broadcast sound in all directions, and even directional sound technologies still generate audible sound along their entire path. We aimed to develop a method that allows sound to be generated only at a specific location, without any leakage along the way. This would enable applications such as private speech zones, immersive audio experiences, and spatially controlled sound environments.”

To achieve precise audio targeting, the researchers used a phenomenon known as difference-frequency wave generation. This process involves emitting two ultrasonic beams – sound waves with frequencies beyond the range of human hearing – that intersect at a chosen point. At their intersection, these beams interact to produce a lower-frequency sound wave within the audible range. In their experiments, the team used ultrasonic waves at frequencies of 40 kHz and 39.5 kHz. When these waves converge, they generated an audible sound at 500 Hz, which falls within the typical human hearing range of approximately 20 Hz–20 kHz.

To prevent obstacles like human bodies from blocking the sound beams, the researchers used self-bending beams that follow curved paths instead of travelling in straight lines. They did this by passing ultrasound waves through specially designed metasurfaces, which redirected the waves along controlled trajectories, allowing them to meet at a specific point where the sound is generated.

Manipulative metasurfaces

“Metasurfaces are engineered materials that manipulate wave behaviour in ways that natural materials cannot,” said Zhong. “In our study, we use metasurfaces to precisely control the phase of ultrasonic waves, shaping them into self-bending beams. This is similar to how an optical lens bends light.”

The researchers began with computer simulations to model how ultrasonic waves would travel around obstacles, such as a human head, to determine the optimal design for the sound sources and metasurfaces. These simulations confirmed the feasibility of creating an audible enclave at the intersection of the curved beams. Subsequently, the team constructed a physical setup in a room-sized environment to validate their findings experimentally. The results closely matched their simulations, demonstrating the practical viability of their approach.​

“Our method allows sound to be produced only in an intended area while remaining completely silent everywhere else,” says Zhong. “By using acoustic metasurfaces, we direct ultrasound along curved paths, making it possible to ‘place’ sound behind objects without a direct line of sight. A person standing inside the enclave can hear the sound, but someone just a few centimetres away will hear almost nothing.”

Initially, the team produced a steady 500 Hz sound within the enclave. By allowing the frequencies of the two ultrasonic sources to vary, they generated a broader range of audible sounds, covering the frequencies from 125 Hz–4 kHz. This expanded range includes much of the human auditory spectrum, increasing the potential applications of the technique.

The ability to generate sound in a confined space without any audible leakage opens up many possible applications. Museums and exhibitions could provide visitors with personalized audio experiences without the need for headphones, allowing individuals to hear different information depending on their location. In cars, drivers could receive navigation instructions without disturbing passengers, who could simultaneously listen to music or other content. Virtual and augmented reality applications could benefit from more immersive soundscapes that do not require bulky headsets.

The technology could also enhance secure communications, creating localized zones where sensitive conversations remain private even in shared spaces. In noisy environments, future adaptations of this method might allow for targeted noise cancellation, reducing unwanted sound in specific areas while preserving important auditory information elsewhere.

Future challenges

While their results are promising, the researchers acknowledge several challenges that must be addressed before the technology can be widely implemented. One concern is the intensity of the ultrasonic beams required to generate audible sound at a practical volume. Currently, achieving sufficient sound levels necessitates ultrasonic intensities that may have unknown effects on human health.​

Another challenge is ensuring high-quality sound reproduction. The relationship between the ultrasonic beam parameters and the resulting audible sound is complex, making it difficult to produce clear audio across a wide range of frequencies and volumes.

“We are currently working on improving sound quality and efficiency,” Zhong said. “We are exploring deep learning and advanced nonlinear signal processing methods to optimize sound clarity. Another area of development is power efficiency — ensuring that the ultrasound-to-audio conversion is both effective and safe for practical use. In the long run, we hope to collaborate with industry partners to bring this technology to consumer electronics, automotive audio, and immersive media applications.”

The research is reported in Proceedings of the National Academy of Sciences.

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Join us for an insightful webinar highlighting cutting-edge research in 2D transition-metal dichalcogenides (TMDs) and their applications in quantum optics.

This session will showcase multimodal imaging techniques, including reflection and time-resolved photoluminescence (TRPL), performed with our high-performance MicroTime 100 microscope. Complementary spectroscopic insights are provided through photoluminescence emission measurements using the FluoTime 300 spectrometer, highlighting the unique characteristics of these advanced materials and their potential in next-generation photonic devices.

Whether you’re a researcher, engineer, or enthusiast in nanophotonics and quantum materials, this webinar will offer valuable insights into the characterization and design of van der Waals materials for quantum optical applications. Don’t miss this opportunity to explore the forefront of 2D material spectroscopy and imaging with a leading expert in the field.

Shengxi Huang is an associate professor in the Department of Electrical and Computer Engineering at Rice University. Huang earned her PhD in electrical engineering and computer science at MIT in 2017, under the supervision of Professors Mildred Dresselhaus and Jing Kong. Following that, she did postdoctoral research at Stanford University with Professors Tony Heinz and Jonathan Fan. She obtained her bachelor’s degree with the highest honors at Tsinghua University, China. Before joining Rice, she was an assistant professor in the Department of Electrical Engineering, Department of Biomedical Engineering, and Materials Research Institute at The Pennsylvania State University.

Huang’s research interests involve light-matter interactions of quantum materials and nanostructures, and the development of new quantum optical platforms and biochemical sensing technologies. In particular, her research focuses on (1) understanding optical and electronic properties of new materials such as 2D materials and Weyl semimetals, (2) developing new biochemical sensing techniques with applications in medical diagnosis, and (3) exploring new quantum optical effects and quantum sensing. She is leading the SCOPE (Sensing, Characterization, and OPtoElectronics) Laboratory.

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Multiphoton microscopy is a nonlinear optical imaging technique that enables label-free, damage-free biological imaging. Performed using femtosecond laser pulses to generate two- and three-photon processes, multiphoton imaging techniques could prove invaluable for rapid cancer diagnosis or personalized medicine.

Imaging biological samples with traditional confocal microscopy requires sample slicing and staining to create contrast in the tissue. The nonlinear mechanisms generated by femtosecond laser pulses, however, eliminate the need for labelling or sample preparation, revealing molecular and structural details within tissue and cells while leaving the sample intact.

Looking to bring these benefits to cancer diagnostics, Netherlands-based start-up Flash Pathology is developing a compact, portable multiphoton microscope that creates pathology-quality images in real time, without the need for sample fixation or staining.

Fast and accurate cancer diagnosis with higher harmonic imaging

The inspiration for Flash Pathology came from Marloes Groot of Vrije Universiteit (VU) Amsterdam. While studying multiphoton microscopy of brain tumours, Groot recognized the need for a portable microscope for clinical settings. “This is a really powerful technique,” she says. “I was working on my large laboratory setup and I thought if we start a company, we could transform this into a mobile device.”

Groot teamed up with Frank van Mourik, now Flash Pathology’s CTO, to shrink the imaging device into a compact 60 x 80 x 115 cm system. “Frank made a device that can be transported, in a truck, wheeled through corridors, and still when you plug it in, it’s on and it produces images – for a nonlinear microscope, this is pretty special,” she explains.

Van Mourik has now built several multiphoton microscopes for Flash Pathology, with one of the main achievements the ability to measure samples with extremely low power levels. “When I started in my lab, I used 200 mW of power, but we’ve been able to reduce that to 5 mW,” Groot notes. “We have performed extensive studies to show that our imaging does not affect the tissue.”

Flash Pathology’s multiphoton microscope is designed to provide rapid on-site histologic feedback on excised tissue, such as diagnostic biopsies or tissue from surgical resections. One key application is lung cancer diagnosis, where there is a clinical need for rapid intraoperative feedback on biopsies. The standard histopathological analysis requires extensive sample preparation and can take several days to provide results.

“With lung biopsies, it’s challenging to obtain good diagnostic material,” explains Sylvia Spies, a PhD student at VU Amsterdam. “The lesions can be quite small and it can be difficult to get to the right position and take a good sample, so they use several techniques (fluoroscopy/CT or ultrasound) to find the right position and take multiple biopsies from the lesion. Despite these techniques, the diagnostic yield is still around 70%, so 30% of cases still don’t get a diagnosis and patients might have to come back for a repeat biopsy procedure.”

Multiphoton imaging, on the other hand, can rapidly visualize unprocessed tissue samples, enabling diagnosis in situ. A recent study using Flash Pathology’s microscope to analyse lung biopsies demonstrated that it could image a biopsy sample and provide feedback just 6 min after excision, with an accuracy of 87% – enabling immediate decisions as to whether a further biopsy is required.

“Also, many clinical fields are now focusing on a one-stop-shop with diagnosis and treatment in one procedure,” adds Spies. “Here, you really need a technique that can rapidly determine whether a lesion is benign or malignant.”

The microscope’s impressive diagnostic performance is partly due to its ability to generate four nonlinear signals simultaneously using a single ultrafast femtosecond laser: second- and third-harmonic generation plus two- and three-photon fluorescence. The system then uses filters to spectrally separate these signals, which provide complementary diagnostic information. Second-harmonic generation, for example, is sensitive to non-centrosymmetric structures such as collagen, while third-harmonic generation only occurs at interfaces with differing refractive indices, such as cell membranes or boundaries between the nucleus and cytoplasm.

“What I like about this technique is that you can see similar features as in conventional histology,” says Spies. “You can see structures such as collagen fibres, elastin fibres and cellular patterns, but also cellular details such as the cytoplasm, the nucleus (and its size), nucleoli and cilia. All these tiny details are the same features that the pathologists look at in conventional histology.”

Applying femtosecond lasers for 3D-in-depth visualization

The femtosecond laser plays a key role in enabling multiphoton microscopy. To excite two- and three-photon processes, you need to have two or more photons in the same place at exactly the same time. And the likelihood of this happening increases rapidly when using ultrashort laser pulses.

“The shorter the pulses are in the time domain, the higher the probability that you have an overlap of two pulses in a focal point,” explains Oliver Prochnow, CEO of VALO Innovations, a part of HÜBNER Photonics. “Therefore you need to have a very high-intensity, extremely short laser pulse. The shorter the better.”

The VALO Femtosecond Series of ultrafast fibre lasers can deliver pulses as short as 30 fs, which is achieved by exploiting nonlinear mechanisms to broaden the spectral bandwidth to more than 100 nm. As the optical spectrum and pulse duration are inherently related by Fourier transformation, a broadband spectrum will result in a very short pulse. And the shorter the pulse, at the same average power, the higher its peak power – and the higher the probability of producing multiphoton processes.

“If you decrease the pulse duration by a factor of five, this gives roughly a five times higher signal from two-photon absorption,” says Prochnow. “In contrast, a three-photon process scales with the third power of the intensity and with the inverse of the pulse duration squared. So you have a roughly 25 times higher signal, if you decrease the pulse duration by a factor of five at the same average power.” Crucially, the shorter pulses deliver this high peak power while maintaining a low average power, reducing sample heating and minimizing photobleaching.

The broadband optical spectrum is particularly important for enabling practical three-photon microscopy. The challenge here is that traditional ytterbium-based lasers with a wavelength of around 1030 nm produce a three-photon signal in the UV range, which is too short to be transmitted through standard optics.

The VALO Femtosecond Series overcomes this problem by having a broadband spectrum that extends up to 1140 nm. Frequency tripling then generates a signal with a long enough wavelength to pass through a standard microscope objective, enabling the VALO lasers to excite both two-photon and three-photon processes. “Our lasers provide the opportunity to perform simultaneous three-photon microscopy and two-photon microscopy using a simple fibre laser solution,” says Prochnow.

The lasers include an integrated dispersion pre-compensation unit to compensate for the dispersion of a microscope objective and provide the shortest pulses at the sample. Additionally, the lasers do not require water cooling, making them easy to use or integrate.

Towards future clinical applications

Flash Pathology is currently testing its microscope in several hospitals in the Netherlands, including Amsterdam UMC, as well as the Princess Maxima Center for paediatric oncology. “Sylvia performed a study in their pathology department and for a year measured all kinds of tissue samples that came through,” says Groot. “We also recently installed a device at the Queen Elizabeth Hospital in Glasgow, for a study on mesothelioma.”

With prototypes now available for research use, the company also plans to develop a fully certified multiphoton microscopy system. “Our ultimate goal is to sell a certified medical diagnostic device that will take a biopsy and produce images, but also contain artificial intelligence to help to interpret the images and give diagnostic conclusions about the nature of the illness,” says van Mourik.

Once fully realised in the clinic, the multiphoton microscopy system will provide an invaluable tool for rapid, in situ tissue analysis during bronchoscopy procedures or other operations. The unique combination of four nonlinear imaging modalities, made possible with a single compact femtosecond laser, delivers complementary diagnostic information. “This will be the big gain, to be able to provide a diagnosis bedside during a procedure,” van Mourik concludes.

 

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This episode of the Physics World Weekly podcast features William Phillips, who shared the 1997 Nobel Prize for Physics for his work on cooling and trapping atoms using laser light.

In a wide-ranging conversation with Physics World’s Margaret Harris, Phillips talks about his long-time fascination with quantum physics – which began with an undergraduate project on electron spin resonance. Phillips chats about quirky quantum phenomena such as entanglement and superposition and explains how they are exploited in atomic clocks and quantum computing. He also looks to the future of quantum technologies and stresses the importance of curiosity-led research.

Phillips has spent much of his career at US’s National Institute for Standards and Technology (NIST) in Maryland and he also a professor of physics at the University of Maryland.

 

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Scientists in the US have developed a new type of photovoltaic battery that runs on the energy given off by nuclear waste. The battery uses a scintillator crystal to transform the intense gamma rays from radioisotopes into electricity and can produce more than a microwatt of power. According to its developers at Ohio State University and the University of Toledo, it could be used to power microelectronic devices such as microchips.

The idea of a nuclear waste battery is not new. Indeed, Raymond Cao, the Ohio State nuclear engineer who led the new research effort, points out that the first experiments in this field date back to the early 1950s. These studies, he explains, used a 50 milli-Curie ⁹⁰Sr-⁹⁰Y source to produce electricity via the electron-voltaic effect in p-n junction devices.

However, the maximum power output of these devices was just 0.8 μW, and their power conversion efficiency (PCE) was an abysmal 0.4 %. Since then, the PCE of nuclear voltaic batteries has remained low, typically in the 1–3% range, and even the most promising devices have produced, at best, a few hundred nanowatts of power.

Exploiting the nuclear photovoltaic effect

Cao is confident that his team’s work will change this. “Our yet-to-be-optimized battery has already produced 1.5 μW,” he says, “and there is much room for improvement.”

To achieve this benchmark, Cao and colleagues focused on a different physical process called the nuclear photovoltaic effect. This effect captures the energy from highly-penetrating gamma rays indirectly, by coupling a photovoltaic solar cell to a scintillator crystal that emits visible light when it absorbs radiation. This radiation can come from several possible sources, including nuclear power plants, storage facilities for spent nuclear fuel, space- and submarine-based nuclear reactors or, really, anyplace that happens to have large amounts of gamma ray-producing radioisotopes on hand.

The scintillator crystal Cao and colleagues used is gadolinium aluminium garnet (GAGG), and they attached it to a solar cell made from polycrystalline CdTe. The resulting device measures around 2 x 2 x 1 cm, and they tested it using intense gamma rays emitted by two different radioactive sources, ¹³⁷Cs and ⁶⁰Co, that produced 1.5 kRad/h and 10 kRad/h, respectively. ¹³⁷Cs is the most common fission product found in spent nuclear fuel, while ⁶⁰Co is an activation product.

Enough power for a microsensor

The Ohio-Toledo team found that the maximum power output of their battery was around 288 nW with the ¹³⁷Cs source. Using the ⁶⁰Co irradiator boosted this to 1.5 μW. “The greater the radiation intensity, the more light is produced, resulting in increased electricity generation,” Cao explains.

The higher figure is already enough to power a microsensor, he says, and he and his colleagues aim to scale the system up to milliwatts in future efforts. However, they acknowledge that doing so presents several challenges. Scaling up the technology will be expensive, and gamma radiation gradually damages both the scintillator and the solar cell. To overcome the latter problem, Cao says they will need to replace the materials in their battery with new ones. “We are interested in finding alternative scintillator and solar cell materials that are more radiation-hard,” he tells Physics World.

The researchers are optimistic, though, arguing that optimized nuclear photovoltaic batteries could be a viable option for harvesting ambient radiation that would otherwise be wasted. They report their work in Optical Materials X.

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Researchers in the Netherlands, Austria, and France have created what they describe as the first operating system for networking quantum computers. Called QNodeOS, the system was developed by a team led by Stephanie Wehner at Delft University of Technology. The system has been tested using several different types of quantum processor and it could help boost the accessibility of quantum computing for people without an expert knowledge of the field.

In the 1960s, the development of early operating systems such as OS/360 and UNIX  represented a major leap forward in computing. By providing a level of abstraction in its user interface, an operating system enables users to program and run applications, without having to worry about how to reconfigure the transistors in the computer processors. This advance laid the groundwork for the many of the digital technologies that have revolutionized our lives.

“If you needed to directly program the chip installed in your computer in order to use it, modern information technologies would not exist,” Wehner explains. “As such, the ability to program and run applications without needing to know what the chip even is has been key in making networks like the Internet actually useful.”

Quantum and classical

The users of nascent quantum computers would also benefit from an operating system that allows quantum (and classical) computers to be connected in networks. Not least because most people are not familiar with the intricacies of quantum information processing.

However, quantum computers are fundamentally different from their classical counterparts, and this means a host of new challenges faces those developing network operating systems.

“These include the need to execute hybrid classical–quantum programs, merging high-level classical processing (such as sending messages over a network) with quantum operations (such as executing gates or generating entanglement),” Wehner explains.

Within these hybrid programs, quantum computing resources would only be used when specifically required. Otherwise, routine computations would be offloaded to classical systems, making it significantly easier for developers to program and run their applications.

No standardized architecture

In addition, Wehner’s team considered that, unlike the transistor circuits used in classical systems, quantum operations currently lack a standardized architecture – and can be carried out using many different types of qubits.

Wehner’s team addressed these design challenges by creating a QNodeOS, which is a hybridized network operating system. It combines classical and quantum “blocks”, that provide users with a platform for performing quantum operations.

“We implemented this architecture in a software system, and demonstrated that it can work with different types of quantum hardware,” Wehner explains. The qubit-types used by the team included the electronic spin states of nitrogen–vacancy defects in diamond and the energy levels of individual trapped ions.

Multi-tasking operation

“We also showed how QNodeOS can perform advanced functions such as multi-tasking. This involved the concurrent execution of several programs at once, including compilers and scheduling algorithms.”

QNodeOS is still a long way from having the same impact as UNIX and other early operating systems. However, Wehner’s team is confident that QNodeOS will accelerate the development of future quantum networks.

“It will allow for easier software development, including the ability to develop new applications for a quantum Internet,” she says. “This could open the door to a new area of quantum computer science research.”

The research is described in Nature.

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The nervous system is often considered the body’s wiring, sending electrical signals to communicate needs and hazards between different parts of the body. However, researchers at the University of Massachusetts at Amherst have now also measured bioelectronic signals propagating from cultured epithelial cells, as they respond to a critical injury.

“Cells are pretty amazing in terms of how they are making collective decisions, because it seems like there is no centre, like a brain,” says researcher Sunmin Yu, who likens epithelial cells to ants in the way that they gather information and solve problems. Alongside lab leader Steve Granick, Yu reports this latest finding in Proceedings of the National Academy of Sciences, suggesting a means for the communication between cells that enables them to coordinate with each other.

While neurons function by bioelectric signals, and punctuated rhythmic bioelectrical signals allow heart muscle cells to keep the heart pumping blood throughout our body, when it comes to intercell signals for any other type of cell, the most common hypothesis is the exchange of chemical cues. Yu, however, had noted from previous work by other groups that the process of “extruding” wounded epithelial cells to get rid of them involved increased expression of the relevant proteins at some distance from the wound itself.

“Our thought process was to inquire about the mechanism by which information could be transmitted over the necessary long distance,” says Yu. She realised that common molecular signalling mechanisms, such as extracellular signal-regulated kinase 1/2 (ERK), which has a speed of around 1 mm/s, would be rather slow as a potential conduit.

Epithelial signals measure up

Yu and Granick grew a layer of epithelial cells on a microelectrode array (MEA). While other approaches to measuring electrical activity in cultured cells exist, an MEA has the advantage of combining electrical sensitivity with a long range, enabling the researchers to collect both temporal and spatial information on electrical activity. They then “wounded” the cells by exposing them to an intense focused laser beam.

Following the wound, the researchers observed electrical potential changes with comparable amplitudes and similar shapes to those observed in neurons, but over much longer periods of time. “The signal propagation speed we measured is about 1000 times slower than neurons and 10 times faster than ERK,” says Yu, expressing great interest in whether the “high-pitch speaking” neurons and heart tissue cells communicate with these “low-pitch speaking” epithelial cells, and if so, how.

The researchers noted an apparent threshold in the amplitude of the generated signal required for it to propagate. But for those that met this threshold, propagation of the electric signals spanned regions up to 600 µm for as long as measurements could be recorded, which was 5 h. Given the mechanical forces generated during “cell extrusion”, the researchers hypothesized the likely role of mechanosensitive proteins in generating the signals. Sure enough, inhibiting the mechanosensitive ion channels shut down the generation of electrical signals.

Yu and Granick highlight previous suggestions that electrical potentials in epithelial cells may be important for regulating the coordinated changes that take place during embryogenesis and regeneration, as well as being implicated in cancer. However, this is the first observation of such electrical potentials being generated and propagating across epithelial tissue.

“Yu and Granick have discovered a remarkable new form of electrical signalling emitted by wounded epithelial cells – cells traditionally viewed as electrically passive,” says Seth Fraden, whose lab at Brandeis University in Massachusetts in the US investigates a range of soft matter topics but was not involved in this research.

Fraden adds that it raises an “intriguing” question: “What is the signal’s target? In light of recent findings by Nathan Belliveau and colleagues, identifying the protein Galvanin as a specific electric-field sensor in immune cells, a compelling hypothesis emerges: epithelial cells send these electric signals as distress calls and immune cells – nature’s healers – receive them to rapidly locate and respond to tissue injuries. Such insights may have profound implications for developing novel regenerative therapies and bioelectric devices aimed at accelerating wound healing.”

Adam Ezra Cohen, whose team at Harvard University in the US focuses on innovative technology for probing molecules and cells, and who was not directly involved in this research, also finds the research “intriguing” but raises numerous questions: “What are the underlying membrane voltage dynamics?  What are the molecular mechanisms that drive these spikes? Do similar things happen in intact tissues or live animals?” he asks, adding that techniques such as patch clamp electrophysiology and voltage imaging could address these questions.

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A new technique could reduce the risk of blood clots associated with medical implants, making them safer for patients. The technique, which was developed by researchers at the University of Sydney, Australia, involves coating the implants with highly hydrophilic molecules known as zwitterions, thereby inhibiting the build-up of clot-triggering proteins.

Proteins in blood can stick to the surfaces of medical implants such as heart valves and vascular stents. When this happens, it produces a cascade effect in which multiple mechanisms lead to the formation of extensive clots and fibrous networks. These clots and networks can impair the function of implanted medical devices so much that invasive surgery may be required to remove or replace the implant.

To prevent this from happening, the surfaces of implants are often treated with polymeric coatings that resist biofouling. Hydrophilic polymeric coatings such as polyethylene glycol are especially useful, as their water-loving nature allows a thin layer of water to form between them and the surface of the implants, held in place via hydrogen and/or electrostatic bonds. This water layer forms a barrier that prevents proteins from sticking, or adsorbing, to the implant.

An extra layer of zwitterions

Recently, researchers discovered that polymers coated with an extra layer of small molecules called zwitterions provided even more protection against protein adsorption. “Zwitter” means “hybrid” in German; hence, zwitterions are molecules that carry both positive and negative charge, making them neutrally charged overall. These molecules are also very hydrophilic and easily form tight bonds with water molecules. The resulting layer of water has a structure that is similar to that of bulk water, which is energetically stable.

A further attraction of zwitterionic coatings for medical implants is that zwitterions are naturally present in our bodies. In fact, they make up the hydrophilic phospholipid heads of mammalian cell membranes, which play a vital role in regulating interactions between biological cells and the extracellular environment.

Plasma functionalization

In the new work, researchers led by Sina Naficy grafted nanometre-thick zwitterionic coatings onto the surfaces of implant materials using a technique called plasma functionalization. They found that the resulting structures reduce the amount of fibrinogen proteins that adsorb onto the implants by roughly nine-fold and decrease blood clot formation (thrombosis) by almost 75%.

Naficy and colleagues achieved their results by optimizing the density, coverage and thickness of the coating. This was critical for realizing the full potential of these materials, they say, because a coating that is not fully optimized would not reduce clotting.

Naficy tells Physics World that the team’s main goal is to enhance the surface properties of medical devices. “These devices when implanted are in contact with blood and can readily cause thrombosis or infection if the surface initiates certain biological cascade reactions,” he explains. “Most such reactions begin when specific proteins adsorb on the surface and activate the next stage of cascade. Optimizing surface properties with the aid of zwitterions can control / inhibit protein adsorption, hence reducing the severity of adverse body reactions.”

The researchers say they will now be evaluating the long-term stability of the zwitterion-polymer coatings and trying to scale up their grafting process. They report their work in Communications Materials and Cell Biomaterials.

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The CERN particle-physics lab near Geneva has released plans for the 15bn SwFr (£13bn) Future Circular Collider (FCC) – a huge 91 km circumference machine. The three-volume feasibility study, released on 31 March, calls for the giant accelerator to collide electrons with positrons to study the Higgs boson in unprecedented detail. If built, the FCC would replace the 27 km Large Hadron Collider (LHC), which will come to an end in the early 2040s.

Work on the FCC feasibility study began in 2020 and the report examines the physics objectives, geology, civil engineering, technical infrastructure and territorial and environmental impact. It also looks at the R&D needed for the accelerators and detectors as well as the socioeconomic benefits and cost.

The study, involving some 150 institutes in over 30 countries, took into account some 100 different scenarios for the collider before landing on a ring circumference of 90.7 km that would be built underground at a depth of about 200 m, on average.

The FCC would also contain eight surface sites to access the tunnel with seven in France and one in Switzerland, and four main detectors. “The design is such that there is minimal impact on the surface, but with the best possible physics output,” says FCC study leader Michael Benedikt.

The funding model for the FCC is still a work in progress, but it is estimated that at least two-thirds of the cost of building the FCC-ee will come from CERN’s 24 member states.

Four committees will now review the feasibility study, beginning with CERN’s scientific committee in July. It will then go to a cost-review panel before being reviewed by the CERN council’s scientific and finance committees. In November, the CERN council will then examine the proposal with a decision to go ahead taken in 2028.

If given the green light, construction on the FCC electron-positron machine, dubbed FCC-ee, would begin in 2030 and it would start operations in 2047, a few years after the High Luminosity LHC (HL-LHC) closes down, and run for about 15 years.  It’s main aim would be to study the Higgs boson with a much better precision that the LHC.

The FCC feasibility study then calls for a hadron machine, dubbed FCC-hh, to replace the FCC-ee in the existing 91 km tunnel. It would be a “discovery machine”, smashing together protons at high energy with the aim of creating new particles. If built, the FCC-hh will begin operation in 2073 and run to the end of the century.

The original design energy for the FCC-hh was to reach 100 TeV but that has now been reduced to 85 TeV.  That is mostly due to the uncertainty in magnet technology. The HL-LHC will use 12 T superconducting quadrupole magnets made from niobium-tin (Nb₃Sn) to squeeze the beams to boost the luminosity.

CERN engineers think it is possible to increase that to 14 T and if this was used for the FCC it would result in a collision centre-of-mass energy of about 85 TeV. “It’s a prudent approach at this stage,” noted Fabiola Gianotti, current CERN director-general, adding that the FCC would be “the most extraordinary instrument ever built.”

The original design called for high-temperature superconducting magnets, such as so-called ReBCO tapes, and CERN is looking into such technology. If it came to fruition in the necessary timescales and was implemented in the FCC-hh then it could push the energy to 120 TeV.

China plans

One potential spanner in the works is China’s plans for a very similar machine called the Circular Election-Positron Collider (CEPC). A decision on the CEPC could come this year with construction beginning in 2027.

Yet officials at CERN are not concerned. They point to the fact that many different colliders have been built by CERN, which has the expertise as well as infrastructure to build such a huge collider.  “Even if China goes ahead, I hope the decision is to compete,” says CERN council president Costas Fountas. “Just like Europe did with the LHC when the US started to build the [cancelled] Superconducting Super Collider.”

If the CERN council decides, however, not to go ahead with the FCC, then Gianotti says that other designs to replace the LHC are still on the table such as a linear machine or a demonstrator muon collider.

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I was unprepared for the Roger Penrose that I met in The Impossible Man. As a PhD student training in relativity and quantum gravity at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, I once got to sit next to Penrose. Unsure of what to say to the man whose ideas about black-hole singularities are arguably why I took an interest in becoming a physicist, I asked him how he had come up with the idea for the space-time diagrams now known as “Penrose diagrams”.

Penrose explained to me that he simply couldn’t make sense of space-time without them, that was all. He spoke in kind terms, something I wasn’t quite used to. I was more familiar with people reacting as if my questions were stupid or impertinent. What I felt from Penrose – who eventually shared the 2020 Nobel Prize for Physics with Reinhard Genzel and Andrea Ghez for his work on singularities – was humility and generosity.

The Penrose of The Impossible Man isn’t so much humble as oblivious and, in my reading, quite spoiled

In hindsight, I wonder if I overread him, or if, having been around too many brusque theoretical physicists, my bar as a PhD student was simply too low. The Penrose of The Impossible Man isn’t so much humble as oblivious and, in my reading, quite spoiled. As a teenager he was especially good at taking care of his sister and her friends, generous with his time and thoughtfulness. But it ends there.

As we learn in this biography – written by the Canadian journalist Patchen Barss – one of those young friends, Judith Daniels, later became the object of Penrose’s affection when he was a distinguished faculty member at the University of Oxford in his 40s. A significant fraction of the book is centred on Penrose’s relationship with Daniels, whom he became reacquainted with in the early 1970s when she was an undergraduate studying mathematics at John Cass College in London.

At the time Penrose was unhappily married to Joan, an American he’d met in 1958 when he was a postdoc at the University of Cambridge. In Barss’s telling, Penrose essentially forces Daniels into the position of muse. He writes her copious letters explaining his intellectual ideas and communicating his inability to get his work done without replies from her, which he expects to contain critical analyses of his scientific proposals.

The letters are numerous and obsessive, even when her replies are thin and distant. Eventually, Penrose also begins to request something more – affection and even love. He wants a relationship with her. Barss never exactly states that this was against Daniels’s will, but he offers readers sufficient details of her letters to Penrose that it’s hard to draw another conclusion.

Unanswered questions

Barss was able to read her letters because they had been returned to Penrose after Daniels’s death in 2005. Penrose, however, never re-examined any of them until Barss interviewed him for this biography. This raises a lot of questions that remain unanswered by the end of the book. In particular, why did Daniels continue to participate in a correspondence that was eventually thousands of pages long on Penrose’s side?

Judith Daniels was a significant figure in Penrose’s life, yet her death and memory seem to have been unremarkable to him for much of his later life

My theory is that Daniels felt she owed it to this great man of science. She also confesses at one point that she had a childhood crush on him. Her affection was real, even if not romantic; it is as if she was trapped in the dynamic. Penrose’s lack of curiosity about the letters after her death is also strange to me. Daniels was a significant figure in his life, yet her death and memory seem to have been unremarkable to him for much of his later life.

By the mid-1970s, when Daniels was finally able to separate herself from what was – on Penrose’s side – an extramarital emotional affair, Penrose went seeking new muses. They were always female students of mathematics and physics.

Just when it seems like we’ve met the worst of Penrose’s treatment of women, we’re told about his “physical aggression” toward his eventual ex-wife Joan and his partial abandonment of the three sons they had together. This is glossed over very quickly. And it turns out there is even more.

Penrose, like many of his contemporaries, primarily trained male students. Eventually he did take on one woman, Vanessa Thomas, who was a PhD student in his group at Oxford’s Mathematical Institute, where he’d moved in 1972.

Thomas never finished her PhD; Penrose pursued her romantically and that was the end of her doctorate. As scandalous as this is, I didn’t find the fact of the romance especially shocking because it is common enough in physics, even if it is increasingly frowned upon and, in my opinion, generally inappropriate. For better or worse, I can think of other examples of men in physics who fell in love with women advisees.

But in all the cases I know of, the woman has gone on to complete her degree either under his or someone else’s supervision. In these same cases, the age difference was usually about a decade. What happened with Thomas – who married Penrose in 1988 – seems like the worst-case scenario: a 40-year age difference and a budding star of mathematics, reduced to serving her husband’s career. Professional boundaries were not just transgressed, but obliterated.

Barss chooses not to offer much in the way of judgement about the impact that Penrose had on the women in science whom he made into muses and objects of romantic affection. The only exception is Ivette Fuentes, who was already a star theoretical physicist in her own right when Penrose first met her in 2012. Interview snippets with Fuentes reveal that the one time Penrose spoke of her as a muse, she rejected him and their friendship until he apologized.

No woman, it seems, had ever been able to hold him to the fire before. Fuentes does, however, describe how Penrose gave her an intellectual companion, something she’d previously been denied by the way the physics community is structured around insider “families” and pedigrees. It is interesting to read this in the context of Penrose’s own upbringing as landed gentry.

Gilded childhood

An intellectually precocious child growing up in 1930s England, Penrose is handed every resource for his intellectual potential to blossom. When he notices a specific pattern linking addition and multiplication, an older sibling is on hand to show him there’s a general rule from number theory that explains the pattern. The family at this point, we’re told, has a cook and a maid who doubles as a nanny. Even in a community of people from well-resourced backgrounds, Penrose stands out as an especially privileged example.

When the Second World War starts, his family readily secures safe passage to a comfortable home in Canada – a privilege related to their status as welcomed members of Britain’s upper class and one that was not afforded to many continental European Jewish families at the time (Penrose’s mother and therefore Penrose was Jewish by descent). Indeed, Canada admitted the fewest Jewish refugees of any Allied nation and famously denied entry to the St Louis, which was sent back to Europe, where a third of its 937 Jewish passengers were murdered in the Holocaust.

In Ontario, the Penrose children have a relatively idyllic experience. Throughout the rest of his childhood and his adult life, the path has been continuously smoothed for Penrose, either by his parents (who bought him multiple homes) or mentors and colleagues who believed in his genius. One is left wondering how many other people might have such a distinguished career if, from birth, they are handed everything on a silver platter and never required to take responsibility for anything.

To tell these and later stories, Barss relies heavily on interviews with Penrose. Access to their subject for any biographer is tricky. While it creates a real opportunity for the author, there is also the challenge of having a relationship with someone whose memories you need to question. Barss doesn’t really interrogate Penrose’s memory but seems to take them as gospel.

During the first half of the book, I wondered repeatedly if The Impossible Man is effectively a memoir told in the third person. Eventually, Barss does allow other voices to tell the story. Ultimately, though, this is firmly a book told from Penrose’s point of view. Even the inclusion of Daniels’s story was at least in part at Penrose’s behest.

I found myself wanting to hear more from the women in Penrose’s life. Penrose often saw himself following a current determined by these women. He came, for example, to believe his first wife had essentially trapped him in their relationship by falling for him.

Penrose never takes responsibility for any of his own actions towards the women in his life. So I wondered: how did they see it? What were their lives like? His ex-wife Joan (who died in 2019) and estranged wife Vanessa, who later became a mathematics teacher, both gave interviews for the book. But we learn little about their perspective on the man whose proclivities and career dominated their own lives.

One day there will be another biography of Penrose that will necessarily have distance from its subject because he will no longer be with us. The Impossible Man will be an important document for any future biographer, containing as it does such a close rendering of Penrose’s perspective on his own life.

The cost of genius

When it comes to describing Penrose’s contributions to mathematics and physics, the science writing, especially in the early pages, sings. Barss has a knack for writing up difficult ideas – whether it’s Penrose’s Nobel-prize-winning work on singularities or his attempt at quantum gravity, twistor theory. Overall, the luxurious prose makes the book highly readable.

Sometimes Barss indulges cosmic flourishes in a way that appears to reinforce Penrose’s perspective that the universe is happening to him rather than one over which he has any influence. In the end, I don’t know if we learn the cost of genius, but we certainly learn the cost of not recognizing that we are a part of the universe that has agency.

The final chapter is really Barss writing about himself and Penrose, and the conversations they have together. Penrose has macular degeneration now, so while both are on a visit to Perimeter in 2019, Barss reads some of his letters to Judith back to Penrose. Apparently, Penrose becomes quite emotional in a way that it seems no-one had ever seen – he weeps.

After that, he asks Barss to include the story about Judith. So, on some level, he knows he has erred.

The end of The Impossible Man is devastating. Barss describes how he eventually gains access to two of Penrose’s sons (three with Joan and one with Vanessa). In those interviews, he hears from children who have been traumatized by witnessing what they call “physical aggression” toward their mother. Even so, they both say they’d like to improve their relationship with their father.

Barss then asks a 92-year-old Penrose if he wants to patch things up with his family. His reply: “I feel my life is busy enough and if I get involved with them, it just distracts from other things.” As Barss concludes, Penrose is persistently unwilling to accept that in his life, he has been in the driver’s seat. He has had choices and doesn’t want to take responsibility for that. This, as much as Penrose’s intellectual interests and achievements, is the throughline of the text.

Penrose has shown that he doesn’t really care what others think, as long as he gets what he wants scientifically

The Penrose we meet at the end of The Impossible Man has shown that he doesn’t really care what others think, as long as he gets what he wants scientifically. It’s clear that Barss has a real affection for him, which makes his honesty about the Penrose he finds in the archives all the more remarkable. Perhaps motivated by generosity toward Penrose, Barss also lets the reader do a lot of the analysis.

I wonder, though, how many physicists who are steeped in this culture, and don’t concern themselves with gender equity issues, will miss how bad some of Penrose’s behaviour has been, as his colleagues at the time clearly did. The only documented objections to his behaviour seem more about him going off the deep end with his research into consciousness, cyclic theory and attacks on cosmic inflation.

As I worked on this review, I considered whether a different reviewer would have simply complained that the book has lots of stuff about Penrose’s personal messes that we don’t need to know. Maybe, to other readers, Penrose doesn’t come off quite as badly. For me, I prefer the hero I met in person rather than in the pages of this book. The Impossible Man is an important text, but it’s heartbreaking in the end.

• 2024 Basic Books (US)/Atlantic Books (UK) 352pp $32/£25hb
• In 2015 Physics World’s Tushna Commissariat interviewed Roger Penrose about his career. You can watch the video below

 

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Agrivoltaics is an interdisciplinary research area that lies at the intersection of photovoltaics (PVs) and agriculture. Traditional PV systems used in agricultural settings are made from silicon materials and are opaque. The opaque nature of these solar cells can block sunlight reaching plants and hinder their growth. As such, there’s a need for advanced semi-transparent solar cells that can provide sufficient power but still enable plants to grow instead of casting a shadow over them.

In a recent study headed up at the Institute for Microelectronics and Microsystems (IMM) in Italy, Alessandra Alberti and colleagues investigated the potential of semi-transparent perovskite solar cells as coatings on the roof of a greenhouse housing radicchio seedlings.

Solar cell shading an issue for plant growth

Opaque solar cells are known to induce shade avoidance syndrome in plants. This can cause morphological adaptations, including changes in chlorophyll content and an increased leaf area, as well as a change in the metabolite profile of the plant. Lower UV exposure can also reduce polyphenol content – antioxidant and anti-inflammatory molecules that humans get from plants.

Addressing these issues requires the development of semi-transparent PV panels with high enough efficiencies to be commercially feasible. Some common panels that can be made thin enough to be semi-transparent include organic and dye-sensitized solar cells (DSSCs). While these have been used to provide power while growing tomatoes and lettuces, they typically only have a power conversion efficiency (PCE) of a few percent – a more efficient energy harvester is still required.

A semi-transparent perovskite solar cell greenhouse

Perovskite PVs are seen as the future of the solar cell industry and show a lot of promise in terms of PCE, even if they are not yet up to the level of silicon. However, perovskite PVs can also be made semi-transparent.

In this latest study, the researchers designed a laboratory-scale greenhouse using a semi-transparent europium (Eu)-enriched CsPbI₃ perovskite-coated rooftop and investigated how radicchio seeds grew in the greenhouse for 15 days. They chose this Eu-enriched perovskite composition because CsPbI₃ has superior thermal stability compared with other perovskites, making it ideal for long exposures to the Sun’s rays. The addition of Eu into the CsPbI₃ structure improved the perovskite stability by minimizing the number of intrinsic defects and increasing the surface-to-volume ratio of perovskite grains.

Alongside this stability, this perovskite also has no volatile components that could potentially effuse under high surface temperatures. It also typically possesses a high PCE – the record for this composition is 21.15%, which is significantly higher and much more commercially feasible than previously possible with organic PVs and DSSCs. This perovskite, therefore, provides a good trade-off between the PCE that can be achieved while transmitting enough light to allow the seedlings to grow.

Low light conditions promote seedling growth

Even though the seedlings were exposed to lower light conditions than natural light, the team found that they grew more quickly, and with bigger leaves, than those under glass panels. This is attributed to the perovskite acting as a filter for only red light to pass through. And red light is known to improve the photosynthetic efficiency and light absorption capabilities of plants, as well as increase the levels of sucrose and hexose within the plant.

The researchers also found that seedlings grown under these conditions had different gene expression patterns compared with those grown under glass. These expression patterns were associated with environmental stress responses, growth regulation, metabolism and light perception, suggesting that the seedlings naturally adapted to different light conditions – although further research is needed to see whether these adaptations will improve the crop yield.

Overall, the use of perovskite PVs strikes a good balance between being able to provide enough power to cover the annual energy needs for irrigation, lighting and air conditioning, while still allowing the seedlings to grow – and grow much quicker and faster. The team suggest that the perovskite solar cells could help with indoor food production operations in the agricultural sector as a potentially affordable solution, although more work now needs to be done on much larger scales to test the technology’s commercial feasibility.

The research is published in Nature Communications.

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The first results from the Dark Energy Spectroscopic Instrument (DESI) are a cosmological bombshell, suggesting that the strength of dark energy has not remained constant throughout history. Instead, it appears to be weakening at the moment, and in the past it seems to have existed in an extreme form known as “phantom” dark energy.

The new findings have the potential to change everything we thought we knew about dark energy, a hypothetical entity that is used to explain the accelerating expansion of the universe.

“The subject needed a bit of a shake-up, and we’re now right on the boundary of seeing a whole new paradigm,” says Ofer Lahav, a cosmologist from University College London and a member of the DESI team.

DESI is mounted on the Nicholas U Mayall four-metre telescope at Kitt Peak National Observatory in Arizona, and has the primary goal of shedding light on the “dark universe”.  The term dark universe reflects our ignorance of the nature of about 95% of the mass–energy of the cosmos.

Intrinsic energy density

Today’s favoured Standard Model of cosmology is the lambda–cold dark matter (CDM) model. Lambda refers to a cosmological constant, which was first introduced by Albert Einstein in 1917 to keep the universe in a steady state by counteracting the effect of gravity. We now know that universe is expanding at an accelerating rate, so lambda is used to quantify this acceleration. It can be interpreted as an intrinsic energy density that is driving expansion. Now, DESI’s findings imply that this energy density is erratic and even more mysterious than previously thought.

DESI is creating a humungous 3D map of the universe. Its first full data release comprise 270 terabytes of data and was made public in March. The data include distance and spectral information about 18.7 million objects including 12.1 million galaxies and 1.6 million quasars. The spectral details of about four million nearby stars nearby are also included.

This is the largest 3D map of the universe ever made, bigger even than all the previous spectroscopic surveys combined. DESI scientists are already working with even more data that will be part of a second public release.

DESI can observe patterns in the cosmos called baryonic acoustic oscillations (BAOs). These were created after the Big Bang, when the universe was filled with a hot plasma of atomic nuclei and electrons. Density waves associated with quantum fluctuations in the Big Bang rippled through this plasma, until about 379,000 years after the Big Bang. Then, the temperature dropped sufficiently to allow the atomic nuclei to sweep up all the electrons. This froze the plasma density waves into regions of high mass density (where galaxies formed) and low density (intergalactic space). These density fluctuations are the BAOs; and they can be mapped by doing statistical analyses of the separation between pairs of galaxies and quasars.

The BAOs grow as the universe expands, and therefore they provide a “standard ruler” that allows cosmologists to study the expansion of the universe. DESI has observed galaxies and quasars going back 11 billion years in cosmic history.

“What DESI has measured is that the distance [between pairs of galaxies] is smaller than what is predicted,” says team member Willem Elbers of the UK’s University of Durham. “We’re finding that dark energy is weakening, so the acceleration of the expansion of the universe is decreasing.”

As co-chair of DESI’s Cosmological Parameter Estimation Working Group, it is Elbers’ job to test different models of cosmology against the data. The results point to a bizarre form of “phantom” dark energy that boosted the expansion acceleration in the past, but is not present today.

The puzzle is related to dark energy’s equation of state, which describes the ratio of pressure of the universe to its energy density. In a universe with an accelerating expansion, the equation of state will have value that is less than about –1/3. A value of –1 characterizes the lambda–CDM model.

However, some alternative cosmological models allow the equation of state to be lower than –1. This means that the universe would expand faster than the cosmological constant would have it do. This points to a “phantom” dark energy that grew in strength as the universe expanded, but then petered out.

“It’s seems that dark energy was ‘phantom’ in the past, but it’s no longer phantom today,” says Elbers. “And that’s interesting because the simplest theories about what dark energy could be do not allow for that kind of behaviour.”

Dark energy takes over

The universe began expanding because of the energy of the Big Bang. We already know that for the first few billion years of cosmic history this expansion was slowing because the universe was smaller, meaning that the gravity of all the matter it contains was strong enough to put the brakes on the expansion. As the density decreased as the universe expanded, gravity’s influence waned and dark energy was able to take over. What DESI is telling us is that at the point that dark energy became more influential than matter, it was in its phantom guise.

“This is really weird,” says Lahav; and it gets weirder. The energy density of dark energy reached a peak at a redshift of 0.4, which equates to about 4.5 billion years ago. At that point, dark energy ceased its phantom behaviour and since then the strength of dark energy has been decreasing. The expansion of the universe is still accelerating, but not as rapidly. “Creating a universe that does that, which gets to a peak density and then declines, well, someone’s going to have to work out that model,” says Lahav.

Scalar quantum field

Unlike the unchanging dark-energy density described by the cosmological constant, a alternative concept called quintessence describes dark energy as a scalar quantum field that can have different values at different times and locations.

However, Elbers explains that a single field such as quintessence is incompatible with phantom dark energy. Instead, he says that “there might be multiple fields interacting, which on their own are not phantom but together produce this phantom equation of state,” adding that “the data seem to suggest that it is something more complicated.”

Before cosmology is overturned, however, more data are needed. On its own, the DESI data’s departure from the Standard Model of cosmology has a statistical significance 1.7σ. This is well below 5σ, which is considered a discovery in cosmology. However, when combined with independent observations of the cosmic microwave background and type Ia supernovae the significance jumps 4.2σ.

“Big rip” avoided

Confirmation of a phantom era and a current weakening would be mean that dark energy is far more complex than previously thought – deepening the mystery surrounding the expansion of the universe. Indeed, had dark energy continued on its phantom course, it would have caused a “big rip” in which cosmic expansion is so extreme that space itself is torn apart.

“Even if dark energy is weakening, the universe will probably keep expanding, but not at an accelerated rate,” says Elbers. “Or it could settle down in a quiescent state, or if it continues to weaken in the future we could get a collapse,” into a big crunch. With a form of dark energy that seems to do what it wants as its equation of state changes with time, it’s impossible to say what it will do in the future until cosmologists have more data.

Lahav, however, will wait until 5σ before changing his views on dark energy. “Some of my colleagues have already sold their shares in lambda,” he says. “But I’m not selling them just yet. I’m too cautious.”

The observations are reported in a series of papers on the arXiv server. Links to the papers can be found here.

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