German launch vehicle startup Rocket Factory Augsburg (RFA) has replaced its chief executive as it works towards a second chance for its first launch.
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Rep. Mike Rogers claims victory in long-running dispute over Space Command's home
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Astranis has signed a $115 million deal to deliver Taiwan’s first dedicated communications spacecraft, amid an issue with a separate small geostationary satellite launched late last year.
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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.
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.
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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Katalyst and LMO are planning an in-space demonstration in GEO orbit in 2026
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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.”
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.”
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.
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.”
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.
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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Members of Maryland’s congressional delegation expressed confidence that Congress will ultimately reject sharp cuts in NASA science programs proposed by the White House, citing competition with China as one factor.
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Tournear will return to the Space Development Agency on April 17 after a three-month administrative leave
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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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SpaceNews produced the official Show Daily for all three exhibit days of the 38th Space Symposium at the Broadmoor Hotel in Colorado Springs, April 17-20, 2023.
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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.
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).
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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The march toward single broadband terminals that can tap into multiple orbits promises greater resiliency and flexibility. It also centralizes risk in one device. “Single point failures are not ideal,” […]
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Blue Shepard launched six women, including a pop star and TV show host, on a suborbital flight of the company’s New Shepard vehicle April 14.
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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.
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 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.
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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On a clear evening this January, flights out of Miami, Orlando and Fort Lauderdale suddenly ground to a halt. The culprit wasn’t weather or a software glitch — it was […]
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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?
“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.”
Applying heat to a normal, classical pot of water will cause it to evolve from state 1 (not boiling) to state 2 (boiling) at the same rate regardless of whether anyone is watching it (even if it doesn’t seem like it). In the quantum world, however, a system that would normally evolve from one state to the other if left unobserved (blindfolded Zeno) can be “frozen” in place by repeated frequent measurements (eyes-open Zeno).
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.
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.
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.”
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.”
The energy level structure of a population of ultracold 87Rb atoms, evolving in a five-level Hilbert space given by the five spin orientations of the F=2 hyperfine ground state. An applied RF field (red arrows) couples neighbouring quantum states together and allows atoms to “hop” between states. Normally, atoms initially placed in the |F, mF> = |2,2> state would cycle between this state and the other four F=2 states in a process known as Rabi oscillation. However, by introducing a “measurement” – shown here as a laser beam (green arrow) resonant with the transition between the |1,0> state and the |2,0> state – Smerzi and colleagues drastically changed the system’s dynamics, forcing the atoms to oscillate between just the |2,2> and |2,1> states (represented by up and down arrows on the so-called Bloch sphere at right). An additional laser beam (orange arrow) and the detector D were used to monitor the system’s evolution over time.
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.
This article forms part of Physics World‘s contribution to the 2025 International Year of Quantum Science and Technology (IYQ), which aims to raise global awareness of quantum physics and its applications.
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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.
The post Intercalation-based desalination and carbon capture for water and climate sustainability appeared first on Physics World.
NASA and Roscosmos have extended a seat barter agreement for flights to the International Space Station into 2027 that will feature longer Soyuz missions to the station.
The post NASA extends seat barter agreement with Roscosmos into 2027 appeared first on SpaceNews.
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