Physicists at CERN have completed a “test run” for taking antimatter out of the laboratory and transporting it across the site of the European particle-physics facility. Although the test was carried out with ordinary protons, the team that performed it says that antiprotons could soon get the same treatment. The goal, they add, is to study antimatter in places other than the labs that create it, as this would enable more precise measurements of the differences between matter and antimatter. It could even help solve one of the biggest mysteries in physics: why does our universe appear to be made up almost entirely of matter, with only tiny amounts of antimatter?

According to the Standard Model of particle physics, each of the matter particles we see around us – from baryons like protons to leptons such as electrons – should have a corresponding antiparticle that is identical in every way apart from its charge and magnetic properties (which are reversed). This might sound straightforward, but it leads to a peculiar prediction. Under the Standard Model, the Big Bang that formed our universe nearly 14 billion years ago should have generated equal amounts of antimatter and matter. But if that were the case, there shouldn’t be any matter left, because whenever pairs of antimatter and matter particles collide, they annihilate each other in a burst of energy.

Physicists therefore suspect that there are other, more subtle differences between matter particles and their antimatter counterparts – differences that could explain why the former prevailed while the latter all but disappeared. By searching for these differences, they hope to shed more light on antimatter-matter asymmetry – and perhaps even reveal physics beyond the Standard Model.

Extremely precise measurements

At CERN’s Baryon-Antibaryon Symmetry Experiment (BASE) experiment, the search for matter-antimatter differences focuses on measuring the magnetic moment (or charge-to-mass ratio) of protons and antiprotons. These measurements need to be extremely precise, but this is difficult at CERN’s “Antimatter Factory” (AMF), which manufactures the necessary low-energy antiprotons in profusion. This is because essential nearby equipment – including the Antiproton Decelerator and ELENA, which reduce the energy of incoming antiprotons from GeV to MeV – produces magnetic field fluctuations that blur the signal.

To carry out more precise measurements, the team therefore needs a way of transporting the antiprotons to other, better-shielded, laboratories. This is easier said than done, because antimatter needs to be carefully isolated from its environment to prevent it from annihilating with the walls of its container or with ambient gas molecules.

The BASE team’s solution was to develop a device that can transport trapped antiprotons on a truck for substantial distances. It is this device, known as BASE-STEP (for Symmetry Tests in Experiments with Portable Antiprotons), that has now been field-tested for the first time.

Protons on the go

During the test, the team successfully transported a cloud of about 105 trapped protons out of the AMF and across CERN’s Meyrin campus over a period of four hours. Although protons are not the same as antiprotons, BASE-STEP team leader Christian Smorra says they are just as sensitive to disturbances in their environment caused by, say, driving them around. “They are therefore ideal stand-ins for initial tests, because if we can transport protons, we should also be able to transport antiprotons,” he says.

The BASE-STEP device is mounted on an aluminium frame and measures 1.95 m x 0.85 m x 1.65 m. At 850‒900 kg, it is light enough to be transported using standard forklifts and cranes.

Like BASE, it traps particles in a Penning trap composed of gold-plated cylindrical electrode stacks made from oxygen-free copper. To further confine the protons and prevent them from colliding with the trap’s walls, this trap is surrounded by a superconducting magnet bore operated at cryogenic temperatures. The second electrode stack is also kept at ultralow pressures of 10^-19 bar, which Smorra says is low enough to keep antiparticles from annihilating with residual gas molecules. To transport antiprotons instead of protons, Smorra adds, they would just need to switch the polarity of the electrodes.

The transportable trap system, which is detailed in Nature, is designed to remain operational on the road. It uses a carbon-steel vacuum chamber to shield the particles from stray magnetic fields, and its frame can handle accelerations of up to 1g (9.81 m/s²) in all directions over and above the usual (vertical) force of gravity. This means it can travel up and down slopes with a gradient of up to 10%, or approximately 6°.

Once the BASE-STEP device is re-configured to transport antiprotons, the first destination on the team’s list is a new Penning-trap system currently being constructed at the Heinrich Heine University in Düsseldorf, Germany. Here, physicists hope to search for charge-parity-time (CPT) violations in protons and antiprotons with a precision at least 100 times higher than is possible at CERN’s AMF.

“At BASE, we are currently performing measurements with a precision of 16 parts in a trillion,” explains BASE spokesperson Stefan Ulmer, an experimental physicist at Heinrich Heine and a researcher at CERN and Japan’s RIKEN laboratory. “These experiments are the most precise tests of matter/antimatter symmetry in the baryon sector to date, but to make these experiments better, we have no choice but to transport the particles out of CERN’s antimatter factory,” he tells Physics World.

The post Protons take to the road appeared first on Physics World.

Many creative industries rely on cutting-edge digital technologies, so it is not surprising that this sector could easily become an early adopter of quantum computing.

In this episode of the Physics World Weekly podcast I am in conversation with James Wootton, who is chief scientific officer at Moth Quantum. Based in the UK and Switzerland, the company is developing quantum-software tools for the creative industries – focusing on artists, musicians and game developers.

Wootton joined Moth Quantum in September 2024 after working on quantum error correction at IBM. He also has long-standing interest in quantum gaming and creating tools that make quantum computing more accessible. If you enjoyed this interview with Wootton, check out this article that he wrote for Physics World in 2018: “Playing games with quantum computers“.

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Five-body recombination, in which five identical atoms form a tetramer molecule and a single free atom, could be the largest contributor to loss from ultracold atom traps at specific “Efimov resonances”, according to calculations done by physicists in the US. The process, which is less well understood than three- and four-body recombination, could be useful for building molecules, and potentially for modelling nuclear fusion.

A collision involving trapped atoms can be either elastic – in which the internal states of the atoms and their total kinetic energy remain unchanged – or inelastic, in which there is an interchange between the kinetic energy of the system and the internal energy states of the colliding atoms.

Most collisions in a dilute quantum gas involve only two atoms, and when physicists were first studying Bose-Einstein condensates (the ultralow-temperature state of some atomic gases), they suppressed inelastic two-body collisions, keeping the atoms in the desired state and preserving the condensate. A relatively small number of collisions, however, involve three or more bodies colliding simultaneously.

“They couldn’t turn off three body [inelastic collisions], and that turned out to be the main reason atoms leaked out of the condensate,” says theoretical physicist Chris Greene of Purdue University in the US.

Something remarkable

While attempting to understand inelastic three-body collisions, Greene and colleagues made the connection to work done in the 1970s by the Soviet theoretician Vitaly Efimov. He showed that at specific “resonances” of the scattering length, quantum mechanics allowed two colliding particles that could otherwise not form a bound state to do so in the presence of a third particle. While Efimov first considered the scattering of nucleons (protons and neutrons) or alpha particles, the effect applies to atoms and other quantum particles.

In the case of trapped atoms, the bound dimer and free atom are then ejected from the trap by the energy released from the binding event. “There were signatures of this famous Efimov effect that had never been seen experimentally,” Greene says. This was confirmed in 2005 by experiments from Rudolf Grimm’s group at the University of Innsbruck in Austria.

Hundreds of scientific papers have now been written about three-body recombination. Greene and colleagues subsequently predicted resonances at which four-body Efimov recombination could occur, producing a trimer. These were observed almost immediately by Grimm and colleagues. “Five was just too hard for us to do at the time, and only now are we able to go that next step,” says Greene.

Principal loss channel

In the new work, Greene and colleague Michael Higgins modelled collisions between identical caesium atoms in an optical trap. At specific resonances, five-body recombination – in which four atoms combine to produce a tetramer and a free particle – is not only enhanced but becomes the principal loss channel. The researchers believe these resonances should be experimentally observable using today’s laser box traps, which hold atomic gases in a square-well potential.

“For most ultracold experiments, researchers will be avoiding loss as much as possible – they would stay away from these resonances,” says Greene; “But for those of us in the few-body community interested in how atoms bind and resonate and how to describe complicated rearrangement, it’s really interesting to look at these points where the loss becomes resonant and very strong.” This is one technique that can be used to create new molecules, for example.

In future, Greene hopes to apply the model to nucleons themselves. “There have been very few people in the few-body theory community willing to tackle a five-particle collision – the Schrödinger equation has so many dimensions,” he says.

Fusion reactions

He hopes it may be possible to apply the researchers’ toolkit to nuclear reactions. “The famous one is the deuterium/tritium fusion reaction. When they collide they can form an alpha particle and a neutron and release a ton of energy, and that’s the basis of fusion reactors…There’s only one theory in the world from the nuclear community, and it’s such an important reaction I think it needs to be checked,” he says.

The researchers also wish to study the possibility of even larger bound states. However, they foresee a problem because the scattering length of the ground state resonance gets shorter and shorter with each additional particle. “Eventually the scattering length will no longer be the dominant length scale in the problem, and we think between five and six is about where that border line occurs,” Greene says. Nevertheless, higher-lying, more loosely-bound six-body Efimov resonances could potentially be visible at longer scattering lengths.

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

Theoretical physicist Ravi Rau of Louisiana State University in the US is impressed by Greene and Higgins’ work. “For quite some time Chris Greene and a succession of his students and post-docs have been extending the three-body work that they did, using the same techniques, to four and now five particles,” he says. “Each step is much more complicated, and that he could use this technique to extend it to five bosons is what I see as significant.” Rau says, however, that “there is a vast gulf” between five atoms and the number treated by statistical mechanics, so new theoretical approaches may be required to bridge the gap.

The post Five-body recombination could cause significant loss from atom traps appeared first on Physics World.

The Mars rover Perseverance has captured the first image of an aurora as seen from the surface of another planet. The visible-light image, which was taken during a solar storm on 18 March 2024, is not as detailed or as colourful as the high-resolution photos of green swirls, blue shadows and pink whorls familiar to aurora aficionados on Earth. Nevertheless, it shows the Martian sky with a distinctly greenish tinge, and the scientists who obtained it say that similar aurorae would likely be visible to future human explorers.

“Kind of like with aurora here on Earth, we need a good solar storm to induce a bright green colour, otherwise our eyes mostly pick up on a faint grey-ish light,” explains Elise Wright Knutsen, a postdoctoral researcher in the Centre for Space Sensors and Systems at the University of Oslo, Norway. The storm Knutsen and her colleagues captured was, she adds, “rather moderate”, and the aurora it produced was probably too faint to see with the naked eye. “But with a camera, or if the event had been more intense, the aurora will appear as a soft green glow covering more or less the whole sky.”

The role of planetary magnetic fields

Aurorae happen when charged particles from the Sun – the solar wind – interact with the magnetic field around a planet. On Earth, this magnetic field is the product of an internal, planetary-scale magnetic dynamo. Mars, however, lost its dynamo (and, with it, its oceans and its thick protective atmosphere) around four billion years ago, so its magnetic field is much weaker. Nevertheless, it retains some residual magnetization in its southern highlands, and its conductive ionosphere affects the shape of the nearby interplanetary magnetic field. Together, these two phenomena give Mars a hybrid magnetosphere too feeble to protect its surface from cosmic rays, but strong enough to generate an aurora.

Scientists had previously identified various types of aurorae on Mars (and every other planet with an atmosphere in our solar system) in data from orbiting spacecraft. However, no Mars rover had ever observed an aurora before, and all the orbital aurora observations, from Mars and elsewhere, were at ultraviolet wavelengths.

How to spot an aurora on Mars

According to Knutsen, the lack of visible-light, surface-based aurora observations has several causes. First, the visible-wavelength instruments on Mars rovers are generally designed to observe the planet’s bright “dayside”, not to detect faint emissions on its nightside. Second, rover missions focus primarily on geology, not astronomy. Finally, aurorae are fleeting, and there is too much demand for Perseverance’s instruments to leave them pointing at the sky just in case something interesting happens up there.

“We’ve spent a significant amount of time and effort improving our aurora forecasting abilities,” Knutsen says.

Getting the timing of observations right was the most challenging part, she adds. The clock started whenever solar satellites detected events called coronal mass ejections (CMEs) that create unusually strong pulses of solar wind. Next, researchers at the NASA Community Coordinated Modeling Center simulated how these pulses would propagate through the solar system. Once they posted the simulation results online, Knutsen and her colleagues – an international consortium of scientists in Belgium, France, Germany, the Netherlands, Spain, the UK and the US as well as Norway – had a decision to make. Was this CME likely to trigger an aurora bright enough for Perseverance to detect?

If the answer was “yes”, their next step was to request observation time on Perseverance’s SuperCam and Mastcam-Z instruments. Then they had to wait, knowing that although CMEs typically take three days to reach Mars, the simulations are only accurate to within a few hours and the forecast could change at any moment. Even if they got the timing right, the CME might be too weak to trigger an aurora.

“We have to pick the exact time to observe, the whole observation only lasts a few minutes, and we only get one chance to get it right per solar storm,” Knutsen says. “It took three unsuccessful attempts before we got everything right, but when we did, it appeared exactly as we had imagined it: as a diffuse green haze, uniform in all directions.”

Future observations

Writing in Science Advances, Knutsen and colleagues say it should now be possible to investigate how Martian aurorae vary in time and space – information which, they note, is “not easily obtained from orbit with current instrumentation”. They also point out that the visible-light instruments they used tend to be simpler and cheaper than UV ones.

“This discovery will open up new avenues for studying processes of particle transport and magnetosphere dynamics,” Knutsen tells Physics World. “So far we have only reported our very first detection of this green emission, but observations of aurora can tell us a lot about how the Sun’s particles are interacting with Mars’s magnetosphere and upper atmosphere.”

The post This is what an aurora looks like on Mars appeared first on Physics World.

Late on Friday 18 April, the provost of Stony Brook University, where I teach, received a standard letter from the National Science Foundation (NSF), the body that funds much academic research in the US. “Termination of certain awards is necessary,” the e-mail ran, “because they are not in alignment with current NSF priorities”. The e-mail mentioned “NSF Award Id 2318247”. Mine.

The termination notice, forwarded to me a few minutes later, was the same one that 400 other researchers all over the US received the same day, in which the agency, following a directive from the Trump administration, grabbed back $233m in grant money. According to the NSF website, projects terminated were “including but not limited to those on diversity, equity, and inclusion (DEI) and misinformation/disinformation”.

Losing grant money is disastrous for research and for the faculty, postdocs, graduate students and support staff who depend on that support. A friend of mine tried to console me by saying that I had earned a badge of honour for being among the 400 people who threatened the Trump Administration so much that it set out to stop their work. Still, I was baffled. Did I really deserve the axe?

My award, entitled “Social and political dynamics of lab-community relations”, was small potatoes. As the sole principal investigator, I’d hired no postdocs or grad students. I’d also finished most of the research and been given a “no-cost extension” to write it up that was due to expire in a few months. In fact, I’d spent all but $21,432 of the $263,266 of cash.

That may sound like a lot for a humanities researcher, but it barely covered a year of my salary and included indirect costs (to which my grant was subject like any other), along with travel and so on. What’s more, my project’s stated aim was to “enhance the effectiveness of national scientific facilities”, which was clearly within the NSF’s mission.

Such facilities, I had pointed out in my official proposal, are vital if the US is to fulfil its national scientific, technological, medical and educational goals. But friction between a facility and the surrounding community can hamper its work, particularly if the lab’s research is seen as threatening – for example, involving chemical, radiological or biological hazards. Some labs, in fact, have had important, yet perfectly safe, facilities permanently closed out of such fear.

“In an age of Big Science,” I argued, “understanding the dynamics of lab-community interaction is crucial to advancing national, scientific, and public interests.” What’s so contentious about that?

“New bad words”

Maybe I had been careless. After all, Ted Cruz, who chairs the Senate’s commerce committee, had claimed in February that 3400 NSF awards worth over $2 billion made during the Biden–Harris administration had promoted DEI and advanced “neo-Marxist class warfare propaganda”. I wondered if I might have inadvertently used some trigger word that outed me as an enemy of the state.

I knew, for instance, that the Trump Administration had marked for deletion photos of the Enola Gay aircraft, which had dropped an atomic bomb on Hiroshima, in a Defense Department database because officials had not realized that “Gay” was part of the name of the pilot’s mother. Administration officials had made similar misinterpretations in scientific proposals that included the words “biodiversity” and “transgenic”.

Had I used one of those “new bad words”? I ran a search on my proposal. Did it mention “equity”? No. “Inclusion”? Also no. The word “diversity” appeared only once, in the subtitle of an article in the bibliography about radiation fallout. “Neo-Marxist”? Again, no. Sure, I’d read Marx’s original texts during my graduate training in philosophy, but my NSF documents hadn’t tapped him or his followers as essential to my project.

Then I remembered a sentence in my proposal. “Well-established scientific findings,” I wrote, “have been rejected by activists and politicians, distorted by lurid headlines, and fuelled partisan agendas.” These lead in turn to “conspiracy theories, fake facts, science denial and charges of corruption”.

Was that it, I wondered? Had the NSF officials thought that I had meant to refer to the administration’s attacks on climate change science, vaccines, green energy and other issues? If so, that was outrageous! There was not a shred of truth to it – no truth at all!

Ructions and retractions

On 23 April – five days after the NSF termination notice – two researchers at Harvard University put together an online “Terminated NSF grant tracker”, which contained information based on what they found in the NSF database. Curious, I scrolled down to SUNY at Stony Brook and found mine: “Social and political dynamics of lab-community relations”.

I was shocked to discover that almost everything about it in the NSF database was wrong, including the abstract

I was shocked to discover that almost everything about it in the NSF database was wrong, including the abstract. The abstract given for my grant was apparently that of another NSF award, for a study that touched on DEI themes – a legitimate and useful thing to study under any normal regime, but not this one. At last, I had the reason for my grant termination: an NSF error.

The next day, 24 April, I managed to speak to the beleaguered NSF programme director, who was kind and understanding and said there’d been a mistake in the database. When I asked her if it could be fixed she said, “I don’t know”. When I asked her if the termination can be reversed, she said, “I don’t know”. I alerted Stony Brook’s grants-management office, which began to press the NSF to reverse its decision. A few hours later I learned that NSF director Sethuraman Panchanathan had resigned.

I briefly wondered if Panchanathan had been fired because my grant had been bungled. No such luck; he was probably disgusted with the administration’s treatment of the agency. But while the mistake over my abstract evidently wasn’t deliberate, the malice behind my grant’s termination certainly was. Further, doesn’t one routinely double-check before taking such an unprecedented and monumental step as terminating a grant by a major scientific agency?

I then felt guilty about my anger; who was I to complain? After all, some US agencies have been shockingly incompetent lately

I then felt guilty about my anger; who was I to complain? After all, some US agencies have been shockingly incompetent lately. A man was mistakenly sent by the Department of Homeland Security to a dangerous prison in El Salvador and they couldn’t (or wouldn’t) get him back. The Department of Health and Human Services has downplayed the value of vaccines, fuelling a measles epidemic in Texas, while defence secretary Pete Hegseth used the Signal messaging app to release classified military secrets regarding a war in progress to a journalist.

How narcissistic of me to become livid only when personally affected by termination of an award that’s almost over anyway.

A few days later, on 28 April, Stony Brook’s provost received another e-mail about my grant from the NSF. Forwarded to me, it said: “the termination notice is retracted; NSF terminated this project in error”. Since then, the online documents at the NSF, and the information about my grant in the tracker, have thankfully been corrected.

The critical point

In a few years’ time, I’ll put together another proposal to study the difference between the way that US government handles science and the needs of its citizens. I’ll certainly have a lot more material to draw on. Meanwhile, I’ll reluctantly wear my badge of honour. For I deserve it – though not, as I initially thought, because I had threatened the Trump Administration enough that they tried to halt my research.

I got it simply because I’m yet another victim of the Trump Administration’s incompetence.

The post Robert P Crease: ‘I’m yet another victim of the Trump administration’s incompetence’ appeared first on Physics World.

Physicists have set a new upper bound on the interaction strength of dark matter by simulating the collision of two clouds of interstellar plasma. The result, from researchers at Ruhr University Bochum in Germany, CINECA in Italy and the Instituto Superior Tecnico in Portugal, could force a rethink on theories describing this mysterious substance, which is thought to make up more than 85% of the mass in the universe.

Since dark matter has only ever been observed through its effect on gravity, we know very little about what it’s made of. Indeed, various theories predict that dark matter particles could have masses ranging from around 10⁻²² eV to around 10¹⁹ GeV — a staggering 50 orders of magnitude.

Another major unknown about dark matter is whether it interacts via forces other than gravity, either with itself or with other particles. Some physicists have hypothesized that dark matter particles might possess positive and negative “dark charges” that interact with each other via “dark electromagnetic forces”. According to this supposition, dark matter could behave like a cold plasma of self-interacting particles.

Bullet Cluster experiment

In the new study, the team searched for evidence of dark interactions in a cluster of galaxies located several billion light years from Earth. This galactic grouping is known as the Bullet Cluster, and it contains a subcluster that is moving away from the main body after passing through it at high speed.

Since the most basic model of dark-matter interactions relies on the same equations as ordinary electromagnetism, the researchers chose to simulate these interactions in the Bullet Cluster system using the same computational tools they would use to describe electromagnetic interactions in a standard plasma. They then compared their results with real observations of the Bullet Cluster galaxy.

The new work builds on a previous study in which members of the same team simulated the collision of two clouds of standard plasma passing through one another. This study found that as the clouds merged, electromagnetic instabilities developed. These instabilities had the effect of redistributing energy from the opposing flows of the clouds, slowing them down while also broadening the temperature range within them.

Ruling out many of the simplest dark matter theories

The latest study showed that, as expected, the plasma components of the subcluster and main body slowed down thanks to ordinary electromagnetic interactions. That, however, appeared to be all that happened, as the data contained no sign of additional dark interactions. While the team’s finding doesn’t rule out dark electromagnetic interactions entirely, team member Kevin Schoeffler explains that it does mean that these interactions, which are characterized by a parameter known as 𝛼𝐷, must be far weaker than their ordinary-matter counterpart. “We can thus calculate an upper limit for the strength of this interaction,” he says.

This limit, which the team calculated as 𝛼𝐷 < 4 x 10^-25 for a dark matter particle with a mass of 1 TeV, rules out many of the simplest dark matter theories and will require them to be rethought, Schoeffler says. “The calculations were made possible thanks to detailed discussions with scientists working outside of our speciality of physics, namely plasma physicists,” he tells Physics World. “Throughout this work, we had to overcome the challenge of connecting with very different fields and interacting with communities that speak an entirely different language to ours.”

As for future work, the physicists plan to compare the results of their simulations with other astronomical observations, with the aim of constraining the upper limit of the dark electromagnetic interaction even further. More advanced calculations, such as those that include finer details of the cloud models, would also help refine the limit. “These more realistic setups would include other plasma-like electromagnetic scenarios and ‘slowdown’ mechanisms, leading to potentially stronger limits,” Schoeffler says.

The present study is detailed in Physical Review D.

The post Plasma physics sets upper limit on the strength of ‘dark electromagnetism’ appeared first on Physics World.

In the quantum world, observing a particle is not a passive act. If you shine light on a quantum object to measure its position, photons scatter off it and disturb its motion. This disturbance is known as quantum backaction noise, and it limits how precisely physicists can observe or control delicate quantum systems.

Physicists at Swansea University have now proposed a technique that could eliminate quantum backaction noise in optical traps, allowing a particle to remain suspended in space undisturbed. This would bring substantial benefits for quantum sensors, as the amount of noise in a system determines how precisely a sensor can measure forces such as gravity; detect as-yet-unseen interactions between gravity and quantum mechanics; and perhaps even search for evidence of dark matter.

There’s just one catch: for the technique to work, the particle needs to become invisible.

Levitating nanoparticles

Backaction noise is a particular challenge in the field of levitated optomechanics, where physicists seek to trap nanoparticles using light from lasers. “When you levitate an object, the whole thing moves in space and there’s no bending or stress, and the motion is very pure,” explains James Millen, a quantum physicist who studies levitated nanoparticles at Kings College, London, UK. “That’s why we are using them to detect crazy stuff like dark matter.”

While some noise is generally unavoidable, Millen adds that there is a “sweet spot” called the Heisenberg limit. “This is where you have exactly the right amount of measurement power to measure the position optimally while causing the least noise,” he explains.

The problem is that laser beams powerful enough to suspend a nanoparticle tend to push the system away from the Heisenberg limit, producing an increase in backaction noise.

Blocking information flow

The Swansea team’s method avoids this problem by, in effect, blocking the flow of information from the trapped nanoparticle. Its proposed setup uses a standing-wave laser to trap a nanoparticle in space with a hemispherical mirror placed around it. When the mirror has a specific radius, the scattered light from the particle and its reflection interfere so that the outgoing field no longer encodes any information about the particle’s position.

At this point, the particle is effectively invisible to the observer, with an interesting consequence: because the scattered light carries no usable information about the particle’s location, quantum backaction disappears. “I was initially convinced that we wanted to suppress the scatter,” team leader James Bateman tells Physics World. “After rigorous calculation, we arrived at the correct and surprising answer: we need to enhance the scatter.”

In fact, when scattering radiation is at its highest, the team calculated that the noise should disappear entirely. “Even though the particle shines brighter than it would in free space, we cannot tell in which direction it moves,” says Rafał Gajewski, a postdoctoral researcher at Swansea and Bateman’s co-author on a paper in Physical Review Research describing the technique.

Gajewski and Bateman’s result flips a core principle of quantum mechanics on its head. While it’s well known that measuring a quantum system disturbs it, the reverse is also true: if no information can be extracted, then no disturbance occurs, even when photons continuously bombard the particle. If physicists do need to gain information about the trapped nanoparticle, they can use a different, lower-energy laser to make their measurements, allowing experiments to be conducted at the Heisenberg limit with minimal noise.

Putting it into practice

For the method to work experimentally, the team say the mirror needs a high-quality surface and a radius that is stable with temperature changes. “Both requirements are challenging, but this level of control has been demonstrated and is achievable,” Gajewski says.

Positioning the particle precisely at the center of the hemisphere will be a further challenge, he adds, while the “disappearing” effect depends on the mirror’s reflectivity at the laser wavelength. The team is currently investigating potential solutions to both issues.

If demonstrated experimentally, the team says the technique could pave the way for quieter, more precise experiments and unlock a new generation of ultra-sensitive quantum sensors. Millen, who was not involved in the work, agrees. “I think the method used in this paper could possibly preserve quantum states in these particles, which would be very interesting,” he says.

Because nanoparticles are far more massive than atoms, Millen adds, they interact more strongly with gravity, making them ideal candidates for testing whether gravity follows the strange rules of quantum theory.  “Quantum gravity – that’s like the holy grail in physics!” he says.

The post Quantum effect could tame noisy nanoparticles by rendering them invisible appeared first on Physics World.

The UK-based company Delta.g has bagged the 2025 qBIG prize, which is awarded by the Institute of Physics (IOP). Initiated in 2023, qBIG celebrates and promotes the innovation and commercialization of quantum technologies in the UK and Ireland.

Based in Birmingham, Delta.g makes quantum sensors that measure the local gravity gradient. This is done using atom interferometry, whereby laser pulses are fired at a cloud of cold atoms that is freefalling under gravity.

On the Earth’s surface, this gradient is sensitive to the presence of buildings and underground voids such as tunnels. The technology was developed by physicists at the University of Birmingham and in 2022 they showed how it could be used to map out a tunnel below a road on campus. The system has also been deployed in a cave and on a ship to test its suitability for use in navigation.

Challenging to measure

“Gravity is a fundamental force, yet its full potential remains largely untapped because it is so challenging to measure,” explains Andrew Lamb who is co-founder and chief technology officer at Delta.g. “As the first to take quantum technology gravity gradiometry from the lab to the field, we have set a new benchmark for high-integrity, noise-resistant data transforming how we understand and navigate the subsurface.”

Awarded by the IOP, the qBIG prize is sponsored by Quantum Exponential, which is the UK’s first enterprise venture capital fund focused on quantum technology. The winner was announced today at the Economist’s Commercialising Quantum Global 2025 event in London. Delta.g receives a £10,000 unrestricted cash prize; 10 months of mentoring from Quantum Exponential; and business support from the IOP.

Louis Barson, the IOP’s director of science, innovation and skills says, “The IOP’s role as UK and Ireland coordinator of the International Year of Quantum 2025 gives us a unique opportunity to showcase the exciting developments in the quantum sector. Huge congratulations must go to the Delta.g team, whose incredible work stood out in a diverse and fast-moving field.”

Two runners-up were commended by the IOP. One is Glasgow-based  Neuranics, which makes quantum sensors that detect tiny magnetic signals from the human body. This other is Southampton’s Smith Optical, which makes an augmented-reality display based on quantum technology.

The post Delta.g wins IOP’s qBIG prize for its gravity sensors appeared first on Physics World.

The electrochemical reduction of carbon dioxide is used to produce a range of chemical and energy feedstocks including syngas (hydrogen and carbon monoxide), formic acid, methane and ethylene. As well as being an important industrial process, the large-scale reduction of carbon dioxide by electrolysis offers a practical way to capture and utilize carbon dioxide.

As a result, developing new and improved electrochemical processes for carbon-dioxide reduction is an important R&D activity. This work involves identifying which catalyst and electrolyte materials are optimal for efficient production. And when a promising electrochemical system is identified in the lab, the work is not over because the design must be then scaled up to create an efficient and practical industrial process.

Such R&D activities must overcome several challenges in operating and characterizing potential electrochemical systems. These include maintaining the correct humidification of carbon-dioxide gas during the electrolysis process and minimizing the production of carbonates – which can clog membranes and disrupt electrolysis.

While these challenges can be daunting, they can be overcome using the 670 Electrolysis Workstation from US-based Scribner. This is a general-purpose electrolysis system designed to test the materials used in the conversion of electrical energy to fuels and chemical feedstocks – and it is ideal for developing systems for carbon-dioxide reduction.

Turn-key and customizable

The workstation is a flexible system that is both turn-key and customizable. Liquid and gas reactants can be used on one or both of the workstation’s electrodes. Scribner has equipped the 670 Electrolysis Workstation with cells that feature gas diffusion electrodes and membranes from US-based Dioxide Materials. The company specializes in the development of technologies for converting carbon dioxide into fuels and chemicals, and it was chosen by Scribner because Dioxide Materials’ products are well documented in the scientific literature.

The gas diffusion electrodes are porous graphite cathodes through which carbon-dioxide gas flows between input and output ports. The gas can migrate from the graphite into a layer containing a metal catalyst. Membranes are used in electrolysis cells to ensure that only the desired ions are able to migrate across the cell, while blocking the movement of gases.

The system employs a multi-range  ±20 A and 5 V potentiostat for high-accuracy operation over a wide range of reaction rates and cell sizes. The workstation is controlled by Scribner’s FlowCell™ software, which provides full control and monitoring of test cells and comes pre-loaded with a wide range of experimental protocols. This includes electrochemical impedance spectroscopy (EIS) capabilities up to 20 KHz and cyclic voltammetry protocols – both of which are used to characterize the health and performance of electrochemical systems. FlowCell™ also allows users to set up long duration experiments while providing safety monitoring with alarm settings for the purging of gases.

Humidified gas

The 670 Electrolysis Workstation features a gas handling unit that can supply humidified gas to test cells. Adding water vapour to the carbon-dioxide reactant is crucial because the water provides the protons that are needed to convert carbon dioxide to products such as methane and syngas. Humidifying gas is very difficult and getting it wrong leads to unwanted condensation in the system. The 670 Electrolysis Workstation uses temperature control to minimize condensation. The same degree of control can be difficult to achieve in homemade systems, leading to failure.

The workstation offers electrochemical cells with 5 cm² and 25 cm² active areas. These can be used to build carbon-dioxide reduction cells using a range of materials, catalysts and membranes – allowing the performance of these prototype cells to be thoroughly evaluated. By studying cells at these two different sizes, researchers can scale up their electrochemical systems from a preliminary experiment to something that is closer in size to an industrial system. This makes the 670 Electrolysis Workstation ideal for use across university labs, start-up companies and corporate R&D labs.

The workstation can handle, acids, bases and organic solutions. For carbon-dioxide reduction, the cell is operated with a liquid electrolyte on the positive electrode (anode) and gaseous carbon dioxide at the negative electrode (cathode). An electric potential is applied across the electrodes and the product gas comes off the cathode side.

The specific product is largely dependent on the catalyst used at the cathode. If a silver catalyst is used for example, the cell is likely to produce the syngas. If a tin catalyst is used, the product is more likely to be formic acid.

Mass spectrometry

The best way to ensure that the desired products are being made in the cell is to connect the gas output to a mass spectrometer. As a result, Scribner has joined forces with Hiden Analytical to integrate the UK-based company’s HPR-20 mass spectrometer for gas analysis. The Hiden system is specifically configured to perform continuous analysis of evolved gases and vapours from the 670 Electrolysis Workstation.

If a cell is designed to create syngas, for example, the mass spectrometer will determine exactly how much carbon monoxide is being produced and how much hydrogen is being produced. At the same time, researchers can monitor the electrochemical properties of the cell. This allows researchers to study relationships between a system’s electrical performance and the chemical species that it produces.

Monitoring gas output is crucial for optimizing electrochemical processes that minimize negative effects such as the production of carbonates, which is a significant problem when doing carbon dioxide reduction.

In electrochemical cells, carbon dioxide is dissolved in a basic solution. This results in the precipitation of carbonate salts that clog up the membranes in cells, greatly reducing performance. This is a significant problem when scaling up cell designs for industrial use because commercial cells must be very long-lived.

Pulsed-mode operation

One strategy for dealing with carbonates is to operate electrochemical cells in pulsed mode, rather than in a steady state. The off time allows the carbonates to migrate away from electrodes, which minimizes clogging. The 670 Electrolysis Workstation allows users to explore the use of short, second-scale pulses. Another option that researchers can explore is the use of pulses of fresh water to flush carbonates away from the cathode area. These and other options are available in a set of pre-programmed experiments that allow users to explore the mitigation of salt formation in their electrochemical cells.

The gaseous products of these carbonate-mitigation modes can be monitored in real time using Hiden’s mass spectrometer. This allows researchers to identify any changes in cell performance that are related to pulsed operation. Currently, electrochemical and product characteristics can be observed on time scales as short as 100 ms. This allows researchers to fine-tune how pulses are applied to minimize carbonate production and maximize the production of desired gases.

Real-time monitoring of product gases is also important when using EIS to observe the degradation of the electrochemical performance of a cell over time. This provides researchers with a fuller picture of what is happening in a cell as it ages.

The integration of Hiden’s mass spectrometer to the 670 Electrolysis Workstation is the latest innovation from Scribner. Now, the company is working on improving the time resolution of the system so that even shorter pulse durations can be studied by users. The company is also working on boosting the maximum current of the 670 to 100 A.

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As we celebrate the International Year of Quantum Science and Technology, the quantum technology landscape is a swiftly evolving place. From developments in error correction and progress in hybrid classical-quantum architectures all the way to the commercialization of quantum sensors, there is much to celebrate.

An expert in quantum information processing and quantum technology, physicist Mauro Paternostro is based at the University of Palermo and Queen’s University Belfast. He is also editor in chief of the IOP Publishing journal Quantum Science and Technology, which celebrates its 10^th anniversary this year. Paternostro talks to Tushna Commissariat about the most exciting recent developments in the filed, his call for a Quantum Erasmus programme and his plans for the future of the journal.

What’s been the most interesting development in quantum technologies over the last year or so?

I have a straightforward answer as well as a more controversial one. First, the simpler point: the advances in quantum error correction for large-scale quantum registers are genuinely exciting. I’m specifically referring to the work conducted by Mikhail Lukin, Dolev Bluvstein and colleagues at Harvard University, and at the Massachusetts Institute of Technology and QuEra Computing, who built a quantum processor with 48 logical qubits that can execute algorithms while correcting errors in real time. In my opinion, this marks a significant step forward in developing computational platforms with embedded robustness. Error correction plays a vital role in the development of practical quantum computers, and Lukin and colleagues won Physics World’s 2024 Breakthrough of the Year award for their work.

You can listen to Mikhail Lukin and Dolev Bluvstein explain how they used trapped atoms to create 48 logical qubits on the Physics World Weekly podcast.

Now, for the more complex perspective. Aside from ongoing debate about whether Microsoft’s much-discussed eight-qubit topological quantum processor – Majorana 1 – is genuinely using topological qubits, I believe the device will help to catalyze progress in integrated quantum chips. While it may not qualify as a genuine breakthrough in the long run, this moment could be the pivotal turning-point in the evolution of quantum computational platforms. All the major players will likely feel compelled to accelerate their efforts toward the unequivocal demonstration of “quantum chip” capabilities, and such a competitive drive is just want both industry and government need right now.

How do you think quantum technologies will scale up as they emerge from the lab and into real-world applications?

I am optimistic in this regard. In fact, progress is already underway, with quantum-sensing devices and atomic quantum clocks are achieving the levels of technological readiness necessary for practical, real-world applications. In the future, hybrid quantum-high-performance computing (HPC) architectures will play crucial roles in bridging classical data-analysis with whatever the field evolves into, once quantum computers can offer genuine “quantum advantage” over classical machines.

Regarding communication, the substantial push toward networked, large-scale communication structures is noteworthy. The availability of the first operating system for programmable quantum networks opens “highways” toward constructing a large-scale “quantum internet”. This development promises to transform the landscape of communication, enabling new possibilities that we are just beginning to explore.

What needs to be done to ensure that the quantum sector can deliver on its promises in Europe and the rest of the world?

We must prioritize continuity and stability to maintain momentum. The national and supranational funding programmes that have supported developments and achievements over the past few years should not only continue, but be enhanced. I am concerned, however, that the current geopolitical climate, which is undoubtedly challenging, may divert attention and funding away from quantum technologies. Additionally, I worry that some researchers might feel compelled to shift their focus toward areas that align more closely with present priorities, such as military applications. While such shifts are understandable, they may not help us keep pace with the remarkable progress the field has made since governments in Europe and beyond began to invest substantially.

On a related note, we must take education seriously. It would be fantastic to establish a Quantum Erasmus programme that allows bachelor’s, master’s and PhD students in quantum technology to move freely across Europe so that they can acquire knowledge and expertise. We need coordinated national and supranational initiatives to build a pipeline of specialists in this field. Such efforts would provide the significant boost that quantum technology needs to continue thriving.

How can the overlap between quantum technology and artificial intelligence (AI) help each other develop?

The intersection and overlap between AI, high-performance computing, and quantum technologies are significant, and their interplay is, in my opinion, one of the most promising areas of exploration. While we are still in the early stages, we have only just started to tap into the potential of AI-based tools for tackling quantum tasks. We are already witnessing the emergence of the first quantum experiments supported by this hybrid approach to information processing.

The convergence of AI, HPC, and quantum computing would revolutionize how we conceive data processing, analysis, forecasting and many other such tasks. As we continue to explore and refine these technologies, the possibilities for innovation and advancement are vast, paving the way for transformations in various fields.

What do you hope the International Year of Quantum Science and Technology (IYQ) will have achieved, going forward?

The IYQ represents a global acknowledgment, at the highest levels, of the immense potential within this field. It presents a genuine opportunity to raise awareness worldwide about what a quantum paradigm for technological development can mean for humankind. It serves as a keyhole into the future, and IYQ could enable an unprecedented number of individuals – governments, leaders and policymakers alike – to peek though it and glimpse at this potential.

All stakeholders in the field should contribute to making this a memorable year. With IYQ, 2025 might even be considered as “year zero” of the quantum technology era.

As we mark its 10th anniversary, how have you enjoyed your time over the last year as editor-in-chief of the journal Quantum Science and Technology (QST)?

Time flies when you have fun, and this is a good time for me to reflect on the past year. Firstly, I want to express my heartfelt gratitude to Rob Thew, the founding editor-in-chief of QST, for his remarkable leadership during the journal’s early years. With unwavering dedication, he and the rest of the entire editorial board, has established QST as an authoritative and selective reference point for the community engaged in the broad field of quantum science and technology. The journal is now firmly recognized as a leading platform for timely and significant research outcomes. A 94% increase in submissions since our fifth anniversary has led to an impressive 747 submissions from 62 countries in 2024 alone, revealing the growing recognition and popularity of QST among scholars. Our acceptance rate of 27% further demonstrates our commitment to publishing only the highest calibre research.

QST has, over the last 10 years, sought to feature research covering the breadth of the field within our curated focus issues covering topics such as: Quantum optomechanics, Quantum photonics: chips and dots; Quantum software, Perspectives on societal aspects and impacts of quantum technologies and Cold atoms in space.

As we celebrate IYQ, QST will lead the way with several exciting editorial initiatives aimed at disseminating the latest achievements in addressing the essential “pillars” of quantum technologies – computing, communication, sensing, and simulation – while also providing authoritative perspectives and visions for the future. Our focus collections seek research within Quantum technologies for quantum gravity & Focus on perspectives on the future of variational quantum computing.

What are your goals with QST, looking ahead?

As quantum technologies advance into an inter- and multi-disciplinary realm, merging fundamental quantum-science with technological applications, QST is evolving as well. We have an increasing number of submissions addressing the burgeoning area of machine learning-enhanced quantum information processing, alongside pioneering studies exploring the application of quantum computing in fields such as chemistry, materials science and quantitative finance. All of this illustrates how QST is proactive in seizing opportunities to advance knowledge from our community of scholars and authors.

This dynamic growth is a fantastic way to celebrate the journal’s 10th anniversary, especially with the added significant milestone of IYQ. Finally, I want to highlight a matter that is very close to my heart, reflecting a much-needed “duty of care” for our readership. As editor-in-chief, I am honoured to support a journal that is part of the ‘Purpose-Led Publishing’ initiative. I view this as a significant commitment to integrity, ethics, high standards, and transparency, which should be the foundation of any scientific endeavour.

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Researchers in Germany report that they have directly measured a superconducting gap in a hydride sulphide material for the first time. The new finding represents “smoking gun” evidence for superconductivity in these materials, while also confirming that the electron pairing that causes it is mediated by phonons.

Superconductors are materials that conduct electricity without resistance. Many materials behave this way when cooled below a certain transition temperature T_c, but in most cases this temperature is very low. For example, solid mercury, the first superconductor to be discovered, has a T_c of 4.2 K. Superconductors that operate at higher temperatures – perhaps even at room temperature – are thus highly desirable, as an ambient-temperature superconductor would dramatically increase the efficiency of electrical generators and transmission lines.

The rise of the superhydrides

The 1980s and 1990s saw considerable progress towards this goal thanks to the discovery of high-temperature copper oxide superconductors, which have T_cs between 30–133 K. Then, in 2015, the maximum known critical temperature rose even higher thanks to the discovery that a sulphide material, H₃S, has a T_c of 203 K when compressed to pressures of 150 GPa.

This result sparked a flurry of interest in solid materials containing hydrogen atoms bonded to other elements. In 2019, the record was broken again, this time by lanthanum decahydride (LaH₁₀), which was found to have a T_c of 250–260 K, again at very high pressures.

A further advance occurred in 2021 with the discovery of high-temperature superconductivity in cerium hydrides. These novel phases of CeH₉ and another newly-synthesized material, CeH₁₀, are remarkable in that they are stable and display high-temperature superconductivity at lower pressures (about 80 GPa, or 0.8 million atmospheres) than the other so-called “superhydrides”.

But how does it work?

One question left unanswered amid these advances concerned the mechanism for superhydride superconductivity. According to the Bardeen–Cooper–Schrieffer (BCS) theory of “conventional” superconductivity, superconductivity occurs when electrons overcome their mutual electrical repulsion to form pairs. These electron pairs, which are known as Cooper pairs, can then travel unhindered through the material as a supercurrent without scattering off phonons (quasiparticles arising from vibrations of the material’s crystal lattice) or other impurities.

Cooper pairing is characterized by a tell-tale energy gap near what’s known as the Fermi level, which is the highest energy level that electrons can occupy in a solid at a temperature of absolute zero. This gap is equivalent to the maximum energy required to break up a Cooper pair of electrons, and spotting it is regarded as unambiguous proof of that material’s superconducting nature.

For the superhydrides, however, this is easier said than done, because measuring such a gap requires instruments that can withstand the extremely high pressures required for superhydrides to exist and behave as superconductors. Traditional techniques such as scanning tunnelling spectroscopy or angle-resolved photoemission spectroscopy do not work, and there was little consensus on what might take their place.

Planar electron tunnelling spectroscopy

A team led by researchers at Germany’s Max Planck Institute for Chemistry has now stepped in by developing a form of spectroscopy that can operate under extreme pressures. The technique, known as planar electron tunnelling spectroscopy, required the researchers to synthesize highly pure planar tunnel junctions of H₃S and its deuterated equivalent D₃S under pressures of over 100 GPa. Using a technique called laser heating, they created junctions with three parts: a metal, tantalum; a barrier made of tantalum pentoxide, Ta₂O₅; and the H₃S or D₃S superconductors. By measuring the differential conductance across the junctions, they determined the density of electron states in H₃S and D₃S near the Fermi level.

These tunnelling spectra revealed that both H₃S and D₃S have fully open superconducting gaps of 60 meV and 44 meV respectively. According to team member Feng Du, the smaller gap in D₃S confirms that the superconductivity in H₃S comes about thanks to interactions between electrons and phonons – a finding that backs up long-standing predictions.

The researchers hope their work, which they report on in Nature, will inspire more detailed studies of superhydrides. They now plan to measure the superconducting gap of other metal superhydrides and compare them with the covalent superhydrides they studied in this work. “The results from such experiments could help us understand the origin of the high T_c in these superconductors,” Du tells Physics World.

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Researchers on the AEgIS collaboration at CERN have designed an experiment that could soon boost our understanding of how antimatter falls under gravity. Created by a team led by Francesco Guatieri at the Technical University of Munich, the scheme uses modified smartphone camera sensors to improve the spatial resolution of measurements of antimatter annihilations. This approach could be used in rigorous tests of the weak equivalence principle (WEP).

The WEP is a key concept of Albert Einstein’s general theory of relativity, which underpins our understanding of gravity. It suggests that within a gravitational field, all objects of should be accelerated at the same rate, regardless of their mass or whether they are matter or antimatter. Therefore, if matter and antimatter accelerate at different rates in freefall, it would reveal serious problems with the WEP.

In 2023 the ALPHA-g experiment at CERN was the first to observe how antimatter responds to gravity. They found that it falls down, with the tantalizing possibility that antimatter’s gravitational response is weaker than matter’s. Today, there are several experiments that are seeking to improve on this observation.

Falling beam

AEgIS’ approach is to create a horizontal beam of cold antihydrogen atoms and observe how the atoms fall under gravity. The drop will be measured by a moiré deflectometer in which a beam passes through two successive and aligned grids of horizontal slits before striking a position-sensitive detector. As the beam falls under gravity between the grids, the effect is similar to a slight horizontal misalignment of the grids. This creates a moiré pattern – or superlattice – that results in the particles making a distinctive pattern on the detector. By detecting a difference in the measured moiré pattern and that predicted by WEP, the AEgIS collaboration hopes to reveal a discrepancy with general relativity.

However, as Guatieri explains, a number of innovations are required for this to work. “For AEgIS to work, we need a detector with incredibly high spatial resolution. Previously, photographic plates were the only option, but they lacked real-time capabilities.”

AEgIS physicists are addressing this by developing a new vertexing detector. Instead of focussing on the antiparticles directly, their approach detects the secondary particles produced when the antimatter annihilates on contact with the detector. Tracing the trajectories of these particles back to their vertex gives the precise location of the annihilation.

Vertexing detector

Borrowing from industry, the team has created its vertexing detector using an array of modified mobile-phone camera sensors (see figure). Gautieri had already used this approach to measure the real-time positions of low-energy positrons (anti-electrons) with unprecedented precision.

“Mobile camera sensors have pixels smaller than 1 micron,” Guatieri describes. “We had to strip away the first layers of the sensors, which are made to deal with the advanced integrated electronics of mobile phones. This required high-level electronic design and micro-engineering.”

With these modifications in place, the team measured the positions of antiproton annihilations to within just 0.62 micron: making their detector some 35 times more precise than previous designs.

Many benefits

“Our solution, demonstrated for antiprotons and directly applicable to antihydrogen, combines photographic-plate-level resolution, real-time diagnostics, self-calibration and a good particle collection surface, all in one device,” Gautieri says.

With some further improvements, the AEgIS team is confident that their vertexing detector with boost the resolution of the freefall of horizontal antihydrogen beams – allowing rigorous tests of the WEC.

AEgIS team member Ruggero Caravita of Italy’s University of Trento adds, “This game-changing technology could also find broader applications in experiments where high position resolution is crucial, or to develop high-resolution trackers”. He says, “Its extraordinary resolution enables us to distinguish between different annihilation fragments, paving the way for new research on low-energy antiparticle annihilation in materials”.

The research is described in Science Advances.

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A ceremony has been held today to officially open the Ray Dolby Centre at the University of Cambridge. Named after the Cambridge physicist and sound pioneer Ray Dolby, who died in 2013, the facility is the new home of the Cavendish Laboratory and will feature 173 labs as well as lecture halls, workshops, cleanrooms and offices.

Designed by the architecture and interior design practice Jestico + Whiles (who also designed the UK’s £61m National Graphene Institute) and constructed by Bouygues UK, the centre has been funded by £85m from Dolby’s estate as well as £75m from the UK’s Engineering and Physical Sciences Research Council (EPSRC).

Spanning 33 000 m² across five floors, the new centre will house 1100 staff members and students.

The basement will feature microscopy and laser labs containing vibration-sensitive equipment as well as 2500 m² of clean rooms.

The Dolby centre will also serve as a national hub for physics, hosting the Collaborative R&D Environment – a EPSRC National Facility – that will foster collaboration between industry and university researchers and enhance public access to new research.

Parts of the centre will be open to the public, including a café as well as outreach and exhibition spaces that are organised around six courtyards.

The centre also provides a new home for the Cavendish Museum, which includes the model of DNA created by James Watson and Francis Crick as well as the cathode ray tube that was used to discover the electron.

The ceremony today was attended by Dagmar Dolby, president of the Ray and Dagmar Dolby Family Fund, Deborah Prentice, vice-chancellor of the University of Cambridge and physicist Mete Atatüre, who is head of the Cavendish Laboratory.

“The greatest impacts on society – including the Cavendish’s biggest discoveries – have happened because of that combination of technological capability and human ingenuity,” notes  Atatüre. “Science is getting more complex and technically demanding with progress, but now we have the facilities we need for our scientists to ask those questions, in the pursuit of discovering creative paths to the answers – that’s what we hope to create with the Ray Dolby Centre.”

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Physicists have succeeded in making neutrons travel in a curved parabolic waveform known as an Airy beam. This behaviour, which had previously been observed in photons and electrons but never in a non-elementary particle, could be exploited in fundamental quantum science research and in advanced imaging techniques for materials characterization and development.

In free space, beams of light propagate in straight lines. When they pass through an aperture, they diffract, becoming wider and less intense. Airy beams, however, are different. Named for the 19^th-century British scientist George Biddell Airy, who developed the mathematics behind them while studying rainbows, they follow a parabola-shaped path – a property known as self-acceleration – and do not spread out as they travel. Airy beams are also “self-healing”, meaning that they reconstruct themselves after passing through an obstacle that blocked part of the beam.

Scientists have been especially interested in Airy beams since 1979, when theoretical work by the physicist Michael Berry suggested several possible applications for them, says Dmitry Pushin, a physicist at the Institute for Quantum Computing (IQC) and the University of Waterloo, Canada. Researchers created the first Airy beams from light in 2007, followed by an electron Airy beam in 2013.

“Inspired by the unusual properties of these beams in optics and electron experiments, we wondered whether similar effects could be harnessed for neutrons,” Pushin says.

Making such beams out of neutrons turned out to be challenging, however. Because neutrons have no charge, they cannot be shaped by electric fields. Also, lenses that focus neutron beams do not exist.

A holographic approach

A team led by Pushin and Dusan Sarenac of the University at Buffalo’s Department of Physics in the US has now overcome these difficulties using a holographic approach based on a custom-microfabricated silicon diffraction grating. The team made this grating from an array of 6 250 000 micron-sized cubic phase patterns etched onto a silicon slab. “The grating modulates incoming neutrons into an Airy form and the resulting beam follows a curved trajectory, exhibiting the characteristics of a two-dimensional Airy profile at a neutron detector,” Sarenac explains.

According to Pushin, it took years of work to figure out the correct dimensions for the array. Once the design was optimized, however, fabricating it took just 48 hours at the IQC’s nanofabrication facility. “Developing a precise wave phase modulation method using holography and silicon microfabrication allowed us to overcome the difficulties in manipulating neutrons,” he says.

The researchers say the self-acceleration and self-healing properties of Airy beams could improve existing neutron imaging techniques (including neutron scattering and diffraction), potentially delivering sharper and more detailed images. The new beams might even allow for new types of neutron optics and could be particularly useful, for example, when targeting specific regions of a sample or navigating around structures.

Creating the neutron Airy beams required access to international neutron science facilities such as the US National Institute of Standards and Technology’s Center for Neutron Research; the US Department of Energy’s Oak Ridge National Laboratory; and the Paul Scherrer Institute in Villigen, Switzerland. To continue their studies, the researchers plan to use the UK’s ISIS Neutron and Muon Source to explore ways of combining neutron Airy beams with other structured neutron beams (such as helical waves of neutrons or neutron vortices). This could make it possible to investigate complex properties such as the chirality, or handedness, of materials. Such work could be useful in drug development and materials science. Since a material’s chirality affects how its electrons spin, it could be important for spintronics and quantum computing, too.

“We also aim to further optimize beam shaping for specific applications,” Sarenac tells Physics World. “Ultimately, we hope to establish a toolkit for advanced neutron optics that can be tailored for a wide range of scientific and industrial uses.”

The present work is detailed in Physical Review Letters.

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Chatbots could boost students’ interest in maths and physics and make learning more enjoyable. So say researchers in Germany, who have compared the emotional response of students using artificial intelligence (AI) texts to learn physics compared to those who only read traditional textbooks. The team, however, found no difference in test performance between the two groups.

The study has been led by Julia Lademann, a physics-education researcher from the University of Cologne, who wanted to see if AI could boost students’ interested in physics. They did this by creating a customized chatbot using OpenAI’s ChatGPT model with a tone and language that was considered accessible to second-year high-school students in Germany.

After testing the chatbot for factual accuracy and for its use of motivating language, the researchers prompted it to generate explanatory text on proportional relationships in physics and mathematics. They then split 214 students, who had an average age of 11.7, into two groups. One was given textbook material on the topic along with chatbot text, while the control group only got the textbook .

The researchers first surveyed the students’ interest in mathematics and physics and then gave them 15 minutes to review the learning material. Their interest was assessed again afterwards along with the students’ emotional state and “cognitive load” – the mental effort required to do the work – through a series of questionnaires.

Higher confidence

The chatbot was found to significantly enhance students’ positive emotions – including pleasure and satisfaction, interest in the learning material and self-belief in their understanding of the subject — compared with those who only used textbook text. “The text of the chatbot is more human-like, more conversational than texts you will find in a textbook,” explains Lademann. “It is more chatty.”

Chatbot text was also found to reduce cognitive load. “The group that used the chatbot explanation experience higher positive feelings about the subject [and] they also had a higher confidence in their learning comprehension,” adds Lademann.

Tests taken within 30 minutes of the “learning phase” of the experiment, however, found no difference in performance between students that received the AI-generated explanatory text and the control group, despite the former receiving more information. Lademann says this could be due to the short study time of 15 minutes.

The researchers say that while their findings suggest that AI could provide a superior learning experience for students, further research is needed to assess its impact on learning performance and long-term outcomes. “It is also important that this improved interest manifests in improved learning performance,” Lademann adds.

Lademann would now like to see “longer term studies with a lot of participants and with children actually using the chatbot”. Such research would explore the potential key strength of chatbots; their ability to respond in real time to student’s queries and adapt their learning level to each individual student.

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In classical physics, gravity is universally attractive. At the quantum level, however, this may not always be the case. If vast quantities of matter are present within an infinitesimally small volume – at the centre of a black hole, for example, or during the very earliest moments of the universe – space–time becomes curved at scales that approach the Planck length. This is the fundamental quantum unit of distance, and is around 10²⁰ times smaller than a proton.

In these extremely curved regions, the classical theory of gravity – Einstein’s general theory of relativity – breaks down. However, research on loop quantum cosmology offers a possible solution. It suggests that gravity, in effect, becomes repulsive. Consequently, loop quantum cosmology predicts that our present universe began in a so-called “cosmic bounce”, rather than the Big Bang singularity predicted by general relativity.

In a recent paper published in EPL, Edward Wilson-Ewing, a mathematical physicist at the University of New Brunswick, Canada, explores the interplay between loop quantum cosmology and a phenomenon sometimes described as “the echo of the Big Bang”: the cosmic microwave background (CMB). This background radiation pervades the entire visible universe, and it stems from the moment the universe became cool enough for neutral atoms to form. At this point, light was suddenly able to travel through space without being continually scattered by the plasma of electrons and light nuclei that existed before. It is this freshly liberated light that makes up the CMB, so studying it offers clues to what the early universe was like.

What was the motivation for your research?

Observations of the CMB show that the early universe (that is, the universe as it was when the CMB formed) was extremely homogeneous, with relative anisotropies of the order of one part in 10⁴. Classical general relativity has trouble explaining this homogeneity on its own, because a purely attractive version of gravity tends to drive things in the opposite direction. This is because if a region has a higher density than the surrounding area, then according to general relativity, that region will become even denser; there is more mass in that region and therefore particles surrounding it will be attracted to it. Indeed, this is how the small inhomogeneities we do see in the CMB grew over time to form stars and galaxies today.

The main way this gets resolved in classical general relativity is to suggest that the universe experienced an episode of super-rapid growth in its earliest moments. This super-rapid growth is known as inflation, and it can suffice to generate homogeneous regions. However, in general, this requires a very large amount of inflation (much more than is typically considered in most models).

Alternately, if for some reason there happens to be a region that is moderately homogeneous when inflation starts, this region will increase exponentially in size while also becoming further homogenized. This second possibility requires a little more than a minimal amount of inflation, but not much more.

My goal in this work was to explore whether, if gravity becomes repulsive in the deep quantum regime (as is the case in loop quantum cosmology), this will tend to dilute regions of higher density, leading to inhomogeneities being smoothed out. In other words, one of the main objectives of this work was to find out whether quantum gravity could be the source of the high degree of homogeneity observed in the CMB.

What did you do in the paper?

In this paper, I studied spherically symmetric space–times coupled to dust (a simple model for matter) in loop quantum cosmology.  These space–times are known as Lemaître–Tolman–Bondi space–times, and they allow arbitrarily large inhomogeneities in the radial direction. They therefore provide an ideal arena to explore whether homogenization can occur: they are simple enough to be mathematically tractable, while still allowing for large inhomogeneities (which, in general, are very hard to handle).

Loop quantum cosmology predicts several leading-order quantum effects. One of these effects is that space–time, at the quantum level, is discrete: there are quanta of geometry just as there are quanta of matter.  This has implications for the equations of motion, which relate the geometry of space–time to the matter in it: if we take into account the discrete nature of quantum geometry, we have to modify the equations of motion.

These modifications are captured by so-called effective equations, and in the paper I solved these equations numerically for a wide range of initial conditions. From this, I found that while homogenization doesn’t occur everywhere, it always occurs in some regions. These homogenized regions can then be blown up to cosmological scales by inflation (and inflation will further homogenize them).  Therefore, this quantum gravity homogenization process could indeed explain the homogeneity observed in the CMB.

What do you plan to do next?

It is important to extend this work in several directions to check the robustness of the homogenization effect in loop quantum cosmology.  The restriction to spherical symmetry should be relaxed, although this will be challenging from a mathematical perspective. It will also be important to go beyond dust as a description of matter. The simplicity of dust makes calculations easier, but it is not particularly realistic.

Other relevant forms of matter include radiation and the so-called inflaton field, which is a type of matter that can cause inflation to occur. That said, in cosmology, the physics is to some extent independent of the universe’s matter content, at least at a qualitative level. This is because while different types of matter content may dilute more rapidly than others in an expanding universe, and the universe may expand at different rates depending on its matter content, the main properties of the cosmological dynamics (for example, the expanding universe, the occurrence of an initial singularity and so on) within general relativity are independent of the specific matter being considered.

I therefore think it is reasonable to expect that the quantitative predictions will depend on the matter content, but the qualitative features (in particular, that small regions are homogenized by quantum gravity) will remain the same. Still, further research is needed to test this expectation.

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This episode of the Physics World Weekly podcast comes from the Chicago metropolitan area – a scientific powerhouse that is home to two US national labs and some of the country’s leading universities.

Physics World’s Margaret Harris was there recently and met Nadya Mason. She is dean of the Pritzker School of Molecular Engineering at the University of Chicago, which focuses on quantum engineering; materials for sustainability; and immunoengineering. Mason explains how molecular-level science is making breakthroughs in these fields and she talks about her own research on the electronic properties of nanoscale and correlated systems.

Harris also spoke to Jeffrey Spangenberger who leads the Materials Recycling Group at Argonne National Laboratory, which is on the outskirts of Chicago. Spangenberger talks about the challenges of recycling batteries and how we could make it easier to recover materials from batteries of the future. Spangenberger leads the ReCell Center, a national collaboration of industry, academia and national laboratories that is advancing recycling technologies along the entire battery life-cycle.

The post Molecular engineering and battery recycling: developing new technologies in quantum, medicine and energy appeared first on Physics World.

What is the main role of the European Centre for Medium-Range Weather Forecasts (ECMWF)?

Making weather forecasts more accurate is at the heart of what we do at the ECMWF, working in close collaboration with our member states and their national meteorological services (see box below). That means enhanced forecasting for the weeks and months ahead as well as seasonal and annual predictions. We also have a remit to monitor the atmosphere and the environment – globally and regionally – within the context of a changing climate.

How does the ECMWF produce its weather forecasts?

Our task is to get the best representation, in a 3D sense, of the current state of the atmosphere versus key metrics like wind, temperature, humidity and cloud cover. We do this via a process of reanalysis and data assimilation: combining the previous short-range weather forecast, and its component data, with the latest atmospheric observations – from satellites, ground stations, radars, weather balloons and aircraft. Unsurprisingly, using all this observational data is a huge challenge, with the exploitation of satellite measurements a significant driver of improved forecasting over the past decade.

In what ways do satellite measurements help?

Consider the EarthCARE satellite that was launched in May 2024 by the European Space Agency (ESA) and is helping ECMWF to improve its modelling of clouds, aerosols and precipitation. EarthCARE has a unique combination of scientific instruments – a cloud-profiling radar, an atmospheric lidar, a multispectral imager and a broadband radiometer – to infer the properties of clouds and how they interact with solar radiation as well as thermal-infrared radiation emitted by different layers of the atmosphere.

How are you combining such data with modelling?

The ECMWF team is learning how to interpret and exploit the EarthCARE data to directly initiate our models. Put simply, mathematical models that better represent clouds and, in turn, yield more accurate forecasts. Indirectly, EarthCARE is also revealing a clearer picture of  the fundamental physics governing cloud formation, distribution and behaviour. This is just one example of numerous developments taking advantage of new satellite data. We are looking forward, in particular, to fully exploiting next-generation satellite programmes from the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) – including the EPS-SG polar-orbiting system and the Meteosat Third Generation geostationary satellite for continuous monitoring over Europe, Africa and the Indian Ocean.

What other factors help improve forecast accuracy?

We talk of “a day, a decade” improvement in weather forecasting, such that a five-day forecast now is as good as a three-day forecast 20 years ago. A richer and broader mix of observational data underpins that improvement, with diverse data streams feeding into bigger supercomputers that can run higher-resolution models and better algorithms. Equally important is ECMWF’s team of multidisciplinary scientists, whose understanding of the atmosphere and climate helps to optimize our models and data assimilation methods. A case study in this regard is Destination Earth, an ambitious European Union initiative to create a series of “digital twins” – interactive computer simulations – of our planet by 2030. Working with ESA and EUMETSTAT, the ECMWF is building the software and data environment for Destination Earth as well as developing the first two digital twins.

What are these two twins?

Our Digital Twin on Weather-Induced and Geophysical Extremes will assess and predict environmental extremes to support risk assessment and management. Meanwhile, in collaboration with others, the Digital Twin on Climate Change Adaptation complements and extends existing capabilities for the analysis and testing of “what if” scenarios – supporting sustainable development and climate adaptation and mitigation policy-making over multidecadal timescales.

Progress in machine learning and AI has been dramatic over the past couple of years

What kind of resolution will these models have?

Both digital twins integrate sea, atmosphere, land, hydrology and sea ice and their deep connections with a resolution currently impossible to reach. Right now, for example, the ECMWF’s operational forecasts cover the whole globe in a 9 km grid – effectively a localized forecast every 9 km. With Destination Earth, we’re experimenting with 4 km, 2 km, and even 1 km grids.

In February, the ECMWF unveiled a 10-year strategy to accelerate the use of machine learning and AI. How will this be implemented?

The new strategy prioritizes growing exploitation of data-driven methods anchored on established physics-based modelling – rapidly scaling up our previous deployment of machine learning and AI. There are also a variety of hybrid approaches combining data-driven and physics-based modelling.

What will this help you achieve?

On the one hand, data assimilation and observations will help us to directly improve as well as initialize our physics-based forecasting models – for example, by optimizing uncertain parameters or learning correction terms. We are also investigating the potential of applying machine-learning techniques directly on observations – in effect, to make another step beyond the current state-of-the-art and produce forecasts without the need for reanalysis or data assimilation.

How is machine learning deployed at the moment?

Progress in machine learning and AI has been dramatic over the past couple of years – so much so that we launched our Artificial Intelligence Forecasting System (AIFS) back in February. Trained on many years of reanalysis and using traditional data assimilation, AIFS is already an important addition to our suite of forecasts, though still working off the coat-tails of our physics-based predictive models. Another notable innovation is our Probability of Fire machine-learning model, which incorporates multiple data sources beyond weather prediction to identify regional and localized hot-spots at risk of ignition. Those additional parameters – among them human presence, lightning activity as well as vegetation abundance and its dryness – help to pinpoint areas of targeted fire risk, improving the model’s predictive skill by up to 30%.

What do you like most about working at the ECMWF?

Every day, the ECMWF addresses cutting-edge scientific problems – as challenging as anything you’ll encounter in an academic setting – by applying its expertise in atmospheric physics, mathematical modelling, environmental science, big data and other disciplines. What’s especially motivating, however, is that the ECMWF is a mission-driven endeavour with a straight line from our research outcomes to wider societal and economic benefits.

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During this webinar, the key steps of integrating an MRI scanner and MRI Linac into a radiotherapy will be presented, specially focusing on the quality assurance required for the use of the MRI images. Furthermore, the use of phantoms and their synergy with each other across the multi-vendor facility will be discussed.

Akos Gulyban is a medical physicist with a PhD in Physics (in Medicine), renowned for his expertise in MRI-guided radiotherapy (MRgRT). Currently based at Institut Jules Bordet in Brussels, he plays a pivotal role in advancing MRgRT technologies, particularly through the integration of the Elekta Unity MR-Linac system along the implementation of dedicated MRI simulation for radiotherapy.

In addition to his clinical research, Gulyban has been involved in developing quality assurance protocols for MRI-linear accelerator (MR-Linac) systems, contributing to guidelines that ensure safe and effective implementation of MRI-guided radiotherapy.

Gulyban is playing a pivotal role in integrating advanced imaging technologies into radiotherapy, striving to enhance treatment outcomes for cancer patients.

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The presence of hydrogen in a sample is usually a bad thing in neutron scattering experiments, but now researchers in the US have turned the tables on the lightest element and used it to spot fake antique coins.

The scattering of relatively slow moving neutrons from materials provides a wide range of structural information. This is because these “cold” neutrons have wavelengths on par with the separations of atoms in a materials. However, materials that contain large amounts of hydrogen-1 nuclei (protons) can be difficult to study because hydrogen is very good at scattering neutrons in random directions – creating a noisy background signal. Indeed, biological samples containing lots of hydrogen are usually “deuterated” – replacing hydrogen with deuterium – before they are placed in a neutron beam.

However, there are some special cases where this incoherent scattering of hydrogen can be useful – measuring the water content of samples, for example.

Surfeit of hydrogen

Now, researchers in the US and South Korea have used a neutron beam to differentiate between genuine antique coins and fakes. The technique relies on the fact that the genuine coins have suffered corrosion that has resulted in the inclusion of hydrogen-bearing compounds within the coins.

Led by Youngju Kim at Daniel Hussey at the National Institute of Standards and Technology (NIST) in Colorado, the team fired a parallel beam of neutrons through individual coins (see figure). The particles travel with ease through a coin’s original metal, but tend to be scattered by the hydrogen-rich corrosion inclusions. This creates a 2D pattern of high and low intensity regions on a neutron-sensitive screen behind the coin. The coin can be rotated and a series of images taken. Then, the researchers used computed tomography to create a 3D image showing the corroded regions of a coin.

The team used this neutron tomography technique to examine an authentic 19^th century coin that was recovered from a shipwreck, and on a coin that is known to be a replica. Although both coins had surface corrosion, the corrosion extended much deeper into the bulk of the authentic coin than it did in the replica.

The researchers also used a separate technique called neutron grating interferometry to characterize the pores in the surfaces of the coins. Pores are common on the surface of coins that have been buried or submerged. Authentic antique coins are often found buried or submerged, whereas replica coins will be buried or submerged to make them look more authentic.

Small-angle scattering

Neutron grating interferometry looks at the small-angle scattering of neutrons from a sample and focuses on structures that range in size from about 1 nm to 1 micron.

The team found that the authentic coin had many more tiny pores than the replica coin, which was dominated by much larger (millimetre scale) pores.

This observation was expected because when a coin is buried or submerged, chemical reactions cause metals to leach out of its surface, creating millimetre-sized pores. As time progresses, however, further chemical reactions cause corrosion by-products such as copper carbonates to fill in the pores. The result is that the pores in the older authentic coin are smaller than the pores in the newer replica coin.

The team now plans to expand its study to include more Korean coins and other metallic artefacts. The techniques could also be used to pinpoint corrosion damage in antique coins, allowing these areas to be protected using coatings.

As well as being important to coin collectors and dealers, the ability to verify the age of coins is of interest to historians and economists – who use the presence of coins in their research.

The study was done using neutrons from NIST’s research reactor in Maryland. That facility is scheduled to restart in 2026 so the team plans to continue its investigation using a neutron source in South Korea.

The research is described in Scientific Reports.

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The first clear images of Yellowstone’s shallowest magma reservoir have revealed its depth with unprecedented precision, providing information that could help scientists determine how dangerous it is. By pinpointing the reservoir’s location, geophysicists and seismologists from Rice University and the universities of Utah, New Mexico and Texas at Dallas, hope to develop more accurate predictions of when this so-called “supervolcano” will erupt again.

Yellowstone is America’s oldest national park, and it owes its spectacular geysers and hot springs to its location above one of the world’s largest volcanoes. The last major eruption of the Yellowstone supervolcano happened around 630 000 years ago, and was violent enough to create a collapsed crater, or caldera, over 60 km across. Though it shows no sign of repeating this cataclysm anytime soon, it is still an active volcano, and it is slowly forming a new magma reservoir.

Previous estimates of the depth of this magma reservoir were highly imprecise, ranging from three to eight kilometres. Scientists also lacked an accurate location for the reservoir’s top and were unsure how its properties changed with increasing depth.

The latest results, from a team led by Brandon Schmandt and Chenglong Duan at Rice and Jamie Farrell at Utah, show that the reservoir’s top lies 3.8 km below the surface. They also show evidence of an abrupt downward transition into a mixture of gas bubbles and magma filling the pore space of volcanic rock. The gas bubbles are made of mostly H₂O in supercritical form and the magma comprises molten silicic rock such as rhyolite.

Creating artificial seismic waves

Duan and colleagues obtained their result by using a mechanical vibration source (a specialized truck built by the oil and gas firm Dawson Geophysical) to create artificial seismic waves across the ground beneath the northeast portion of Yellowstone’s caldera. They also deployed a network of hundreds of portable seismometers capable of recording both vertical and ground vibrations, spaced at 100 to 150-m intervals, across the national park. “Researchers already knew from previous seismic and geochemical studies that this region was underlain by magma, but we needed new field data and an innovative adaptation of conventional seismic imaging techniques,” explains Schmandt. The new study, he tells Physics World, is “a good example of how the same technologies are relevant to energy industry imaging and studies of natural hazards”.

Over a period of a few days, the researchers created artificial earthquakes at 110 different locations using 20 shocks lasting 40 seconds apiece. This enabled them to generate two types of seismic wave, known as S- and P-waves, which reflect off molten rock at different velocities. Using this information, they were able to locate the top of the magma chamber and determine that 86% of this upper portion was solid rock.

The rest, they discovered, was made up of pores filled with molten material such as rhyolite and volatile gases (mostly water in supercritical form) and liquids in roughly equal proportion. Importantly, they say, this moderate concentration of pores allows the volatile bubbles to gradually escape to the surface so they do not accumulate and increase the buoyancy deeper inside the chamber. This is good news as it means that the Yellowstone supervolcano is unlikely to erupt any time soon.

A key aspect of this analysis was a wave-equation imaging method that Duan developed, which substantially improved the spatial resolution of the features observed. “This was important since we had to adapt the data we obtained to its less than theoretically ideal properties,” Schmandt explains.

The work, which is detailed in Nature, could also help scientists monitor the eruption potential of other volcanos, Schmandt adds. This is because estimating the accumulation and buoyancy of volatile material beneath sharp magmatic cap layers is key to assessing the stability of the system. “There are many types of similar hazardous magmatic systems and their older remnants on our planet that are important for resources like metal ores and critical minerals,” he explains. “We therefore have plenty of targets left to understand and now some refined ideas about how we might approach them in the field and on the computer.”

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“The universe began with a Big Bang.”

I’ve said this neat line more times than I can count at the start of a public lecture. It summarizes one of the most incomprehensible ideas in science: that the universe began in an extreme, hot, dense and compact state, before expanding and evolving into everything we now see around us. The certainty of the simple statement is reassuring, and it is an easy way of quickly setting the background to any story in astronomy.

But what if it isn’t just an oversimplified summary? What if it is misleading, perhaps even wholly inaccurate?

The Battle of the Big Bang: the New Tales of Our Cosmic Origin aims to dismantle the complacency many of us have fallen into when it comes to our knowledge of the earliest time. And it succeeds – if you push through the opening pages.

When a theory becomes so widely accepted that it is immune to question, we’ve moved from science supported by evidence to belief upheld by faith

Early on, authors Niayesh Afshordi and Phil Halper say “in some sense the theory of the Big Bang cannot be trusted”, which caused me to raise an eyebrow and wonder what I had let myself in for. After all, for many astronomers, myself included, the Big Bang is practically gospel. And therein lies the problem. When a theory becomes so widely accepted that it is immune to question, we’ve moved from science supported by evidence to belief upheld by faith.

It is easy to read the first few pages of The Battle of the Big Bang with deep scepticism but don’t worry, your eyebrows will eventually lower. That the universe has evolved from a “hot Big Bang” is not in doubt – observations such as the measurements of the cosmic microwave background leave no room for debate. But the idea that the universe “began” as a singularity – a region of space where the curvature of space–time becomes infinite – is another matter. The authors argue that no current theory can describe such a state, and there is no evidence to support it.

An astronomical crowbar

Given the confidence with which we teach it, many might have assumed the Big Bang theory beyond any serious questioning, thereby shutting the door on their own curiosity. Well, Afshordi and Halper have written the popular science equivalent of a crowbar, gently prising that door back open without judgement, keen only to share the adventure still to be had.

A cosmologist at the University of Waterloo, Canada, Afshordi is obsessed with finding observational ways of solving problems in fundamental physics, and is known for his creative alternative theories, such as a non-constant speed of light. Meanwhile Halper, a science popularizer, has carved out a niche by interviewing leading voices in early universe cosmology on YouTube, often facilitating fierce debates between competing thinkers. The result is a book that is both authoritative and accessible – and refreshingly free from ego.

Over 12 chapters, the book introduces more than two dozen alternatives to the Big Bang singularity, with names as tongue-twisting as the theories are mind-bending. For most readers, and even this astrophysicist, the distinctions between the theories quickly blur. But that’s part of the point. The focus isn’t on convincing you which model is correct, it’s about making clear that many alternatives exist that are all just as credible (give or take). Reading this book feels like walking through an art gallery with a knowledgeable and thoughtful friend explaining each work’s nuance. They offer their own opinions in hushed tones, but never suggest that their favourite should be yours too, or even that you should have a favourite.

If you do find yourself feeling dizzy reading about the details of holographic cosmology or eternal inflation, then it won’t be long before an insight into the nature of scientific debate or a crisp analogy brings you up for air. This is where the co-authorship begins to shine: Halper’s presence is felt in the moments when complicated theories are reduced to an idea anyone can relate to; while Afshordi brings deep expertise and an insider’s view of the cosmological community. These vivid and sometimes gossipy glimpses into the lives and rivalries of his colleagues paint a fascinating picture. It is a huge cast of characters – including Roger Penrose, Alan Guth and Hiranya Peiris – most of whom appear only for a page. But even though you won’t remember all the names, you are left with the feeling that Big Bang cosmology is a passionate, political and philosophical side of science very much still in motion.

Keep the door open

The real strength of this book is its humility and lack of defensiveness. As much as reading about the theory behind a multiverse is interesting, as a scientist, I’m always drawn to data. A theory that cannot be tested can feel unscientific, and the authors respect that instinct. Surprisingly, some of the most fantastical ideas, like pre-Big Bang cosmologies, are testable. But the tools required are almost science fiction themselves – such as a fleet of gravitational-wave detectors deployed in space. It’s no small task, and one of the most delightful moments in the book is a heartfelt thank you to taxpayers, for funding the kind of fundamental research that might one day get us to an answer.

In the concluding chapters, the authors pre-emptively respond to scepticism, giving real thought to discussing when thinking outside the box becomes going beyond science altogether. There are no final answers in this book, and it does not pretend to offer any. In fact, it actively asks the reader to recognize that certainty does not belong at the frontiers of science. Afshordi doesn’t mind if his own theories are proved wrong, the only terror for him is if people refuse to ask questions or pursue answers simply because the problem is seen as intractable.

Curiosity, unashamed and persistent, is far more scientific than shutting the door for fear of the uncertain

A book that leaves you feeling like you understand less about the universe than when you started it might sound like it has failed. But when that “understanding” was an illusion based on dogma, and a book manages to pry open a long-sealed door in your mind, that’s a success.

The Battle of the Big Bang offers both intellectual humility and a reviving invitation to remain eternally open-minded. It reminded me of how far I’d drifted from being one of the fearless schoolchildren who, after I declare with certainty that the universe began with a Big Bang, ask, “But what came before it?”. That curiosity, unashamed and persistent, is far more scientific than shutting the door for fear of the uncertain.

• May 2025 University of Chicago Press 360pp $32.50/£26.00 hb

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The Canadian firm General Fusion is to lay off about 25% of its 140-strong workforce and reduce the operation of its fusion device dubbed Lawson Machine 26 (LM26). The announcement was made in an open letter published on 5 May by the company’s chief executive Greg Twinney. The moves follows what the firm says is an “unexpected and urgent financing constraint”.

Founded in 2002 by the Canadian plasma physicist Michel Laberge, General Fusion is based in Richmond, British Columbia. It is one of the first private fusion companies and has attracted more than $325m of funding from both private investors, including Amazon boss Jeff Bezos and the Canadian government.

The firm is pursuing commercial fusion energy via Magnetized Target Fusion (MTF) technology, based on the concept of an enclosed, liquid-metal vortex. Plasma is injected into the centre of the vortex before numerous pistons hammer on the outside of the enclosure, compressing the plasma and sparking a fusion reaction, with the resulting heat being absorbed by the liquid metal.

LM26 switched on in 2023 and is designed to achieve fusion conditions of over 100 million kelvin. Over the past couple of years, the machine has claimed a number of milestones, including generating a magnetised plasma in the machine’s target chamber in March. Last week, General Fusion also said that LM26 had successfully compressed a large-scale magnetized plasma with lithium.

The firm was hoping to achieve “scientific breakeven equivalent” in the coming years with the aim of potentially building a commercial-scale machine with the technology in the 2030s. But that timescale now looks unlikely as General Fusion announces plans to downscales its efforts due to funding issues. In his letter, Twinney said the firm has “proven a lot with a lean budget”.

Challenging environment 

“Today’s funding landscape is more challenging than ever as investors and governments navigate a rapidly shifting and uncertain political and market climate,” says Twinney. “We are ready to execute our plan but are caught in an economic and geopolitical environment that is forcing us to wait.” But he insists that General Fusion, which his seeking new investors, remains an “attractive opportunity”.

Andrew Holland, chief executive of the non-profit Fusion Industry Association, told Physics World that the “nature of private enterprise is that business cycles go up and go down” and claims that excitement about fusion is growing around the world. “I hope that business cycles and geopolitics don’t interrupt the good work of scientific advancement,” he says. “I’m hopeful investors see the value being created with every experiment.”

The post General Fusion lays off staff due to ‘unexpected and urgent financing constraints’ appeared first on Physics World.

In a sunny office, Ji-Seon Kim holds up a sheet of stripy plastic. In the middle of dark blue and transparent bands, a small red glow catches the eye, clearly visible even against the bright daylight. There are no sockets or chargers, but that little light is no magic trick.

“It’s a printed solar cell from my industrial collaborator,” Kim explains. “This blue material is the organic semiconductor printed in the plastic. It absorbs indoor light and generates electricity to power the LED.”

Kim is a professor in the Department of Physics at Imperial College London, and was director of the university’s EPSRC Plastic Electronics Centre for Doctoral Training, which closed in 2023. She researches carbon-based semiconductors, sometimes called organic, molecular or plastic semiconductors. In 2023 the Institute of Physics (IOP) awarded her the Nevill Mott Medal and Prize in recognition of her “outstanding contributions to the materials physics” of this area.

Yet she came to the field almost by accident. After completing her master’s degree in theoretical physics in Seoul in 1994, Kim was about to embark on a theory-focused PhD studying nonlinear optics at Imperial, when her master’s supervisor told her about some exciting work happening at the University of Cambridge.

A team there had just created the first organic light-emitting diodes (OLEDs) based on conjugated polymers, successfully stimulating carbon-based molecules to glow under an applied voltage. Intrigued by the nascent field, Kim contacted Richard Friend, who led the research and, following an interview, he offered her a PhD position. Friend himself won the IOP’s Isaac Newton Medal and Prize in 2024.

I was really lucky to be in the right place at the right time, just after this new discovery

Ji-Seon Kim

“I spent almost six months learning how to use certain equipment in the lab,” Kim recalls of the tricky transition from theory to experimental work. “For example, there’s a big glove box you have to put your hands in to make the devices inside it, and I wasn’t sure whether I was even able to open the chamber.”

But as she found her feet, she became increasingly passionate about the work. “I was really lucky to be in the right place at the right time, just after this new discovery.”

Seeing the light

You could hardly find a clearer example of fundamental research moving into consumer applications in recent years than OLEDs – now a familiar term in the world of TVs and smartphones. But when Kim joined the field, the first OLEDs were inefficient and degraded quickly due to high electric fields, heat and oxygen exposure. So, during her PhD, Kim focused on making the devices more efficient and last for longer.

She also helped to develop a better understanding of the physics underlying the phenomenon. At the time, researchers disagreed about the fundamental limit of device efficiency determined by excited state (singlet vs triplet) formation under charge injection. Drawing on her theoretical background, Kim developed innovative simulation work on display device outcoupling, which provided a new way of determining the orientation of emitting molecules and the device efficiency, which is now commonly used in the OLED community.

Kim completed her PhD in 2000 and continued studying organic semiconductors, moving to Imperial in 2007. Besides display screens, she is interested in numerous other potential applications of the materials, including sustainable energy. After all, just as the molecules can emit light in response to injected charges, so too can they absorb photons and generate electricity.

Organic semiconductors have several advantages over traditional silicon-based photovoltaic materials. As well as being lightweight, carbon molecules can be tuned to absorb different wavelengths. Whereas silicon solar cells only work with sunlight, and must be installed as heavy panels on roofs or in fields, organic semiconductors offer more options. They could be inconspicuously integrated into buildings, capturing indoor office light that is normally wasted and using it to power appliances. They could even be made into a transparent film and incorporated into windows to convert sunlight into electricity.

Plastic fabrication methods offer a further benefit. Unlike silicon, carbon-based semiconductors can be dissolved in common organic solvents to create a kind of ink, opening the door to low-cost, flexible printing techniques.

And it doesn’t stop there. “A future direction I am particularly interested in is using organic semiconductors for neuromorphic applications,” says Kim. “You can make synaptic transistors – which mimic biological neurons – using molecular semiconductors.”

With all the promise of these materials, the field has flourished. Kim’s group is currently tackling the challenge of the high binding energy between the electron–hole pair in organic semiconductors, which resists separation into free charges, increasing the intrinsic energy cost of using them. Kim and her team are exploring new small molecules, which create an energy level offset by simply changing their packing and orientations, providing an extra driving force to separate the charges.

Building bridges

Alongside her work at Imperial, Kim was also a visiting professor at KAIST in Korea, and is actively involved in strengthening UK–Korea research ties. In 2016 she co-established the GIST-ICL Research and Development Centre for Plastic Electronics, a collaboration between the Gwangju Institute for Science and Technology and Imperial.

“International interactions are critical not only for scientific development but also for future technology,” Kim says. “The UK is really strong in fundamental science, but we don’t have many manufacturing sites compared to Asian countries like Korea. For a fundamental discovery to be applied in a commercial device, there’s a transition from the lab to the manufacturing scale. For that we need a partner, and those partners are overseas.”

Kim is also seeking to build bridges across disciplines. She will soon be moving to the University of Oxford to work on physical chemistry as part of a research initiative focused on sustainable materials and chemistry. She will draw on her expertise in spectroscopic techniques to study and engineer molecules for sustainable applications.

“These days physics is multidisciplinary,” she notes. “For future technology and science, you have to be able to integrate different disciplines. I hope I can contribute as a physicist to bridge different disciplines in molecular semiconductors.”

But one constant is how Kim mentors undergraduate students. Her advice is to engage them with innovations from the lab, which is why she likes to get out the plastic sheet powering the LED. The emphasis on tangible experience is inspired by the excitement and motivation she remembers feeling when she saw organic semiconductors glowing at the start of her PhD.

“Even though the efficiency was so poor that we had to turn the overhead light off and use a really high voltage to see the faint light, that exposure to the real physics was really important,” she says. “That was for me a Eureka moment.”

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What does the word “overselling” mean to you? At one level, it can just mean selling more of something than already exists or can be delivered. It’s what happens when airlines overbook flights by selling more seats than physically exist on their planes. They assume a small fraction of passengers won’t turn up, which is fine – until you can’t fly because everyone else has rocked up ahead of you.

Overselling can also involve selling more of something than is strictly required. Also known as “upselling”, you might have experienced it when buying a car or taking out a new broadband contract. You end up paying for extras and add-ons that were offered but you didn’t really need or even want, which explains why you’ve got all those useless WiFi boosters lying around the house.

There’s also a third meaning of “overselling”, which is to exaggerate the merits of something. You see it when a pharmaceutical company claims its amazing anti-ageing product “will make you live 20 years longer”, which it won’t. Overselling in this instance means overstating a product’s capability or functionality. It’s pretending something is more mature than it is, or claiming a technology is real when it’s still at proof-of-concept-stage.

From my experience in science and technology, this form of overselling often happens when companies and their staff want to grab attention or to keep customers or consumers on board. Sometimes firms do it because they are genuinely enthusiastic (possibly too much so) about the future possibilities of their product. I’m not saying overselling is necessarily a bad thing but just that there are reservations.

Fact and fiction

Before I go any further, let’s learn the lingo of overselling. First off, there’s “vapourware”, which refers to a product that either doesn’t exist or doesn’t fulfil the stated technical capability. Often, it’s something a firm wants to include in its product portfolio because they’re sure people would like to own it. Deep down, though, the company knows the product simply isn’t possible, at least not right now. Like a vapour, it’s there but can’t be touched.

Sometimes vapourware is just a case of waiting for product development to catch up with a genuine product plan. Sales staff know they haven’t got the product at the right specification yet, and while the firm will definitely get there one day, they’re pretending the hurdles have already been crossed. But genuine over-enthusiasm can sometimes cross over into wishful thinking – the idea that a certain functionality can be achieved with an existing technical approach.

Do you remember Google Glass? This was wearable tech, integrated into spectacle frames, that was going to become the ubiquitous portable computer. Information would be requested via voice commands, with the user receiving back the results, visible on a small heads-up display. While the computing technology worked, the product didn’t succeed. Not only did it look clunky, there were also deployment constraints and concerns about privacy and safety.

Google Glass simply didn’t capture the public’s imagination or meet the needs of enough consumers

Google Glass failed on multiple levels and was discontinued in 2015, barely a year after it hit the market. Subsequent relaunches didn’t succeed either and the product was pulled for a final time in 2023. Despite Google’s best efforts, the product simply didn’t capture the public’s imagination or meet the needs of enough consumers.

Next up in our dictionary of vapourware is “unobtanium”, which is a material or material specification that we would like to exist, but simply doesn’t. In the aerospace sector, where I work, we often dream of unobtanium. We’re always looking for materials that can repeatedly withstand the operational extremes encountered during a flight, while also being sustainable without cutting corners on safety.

Like other engine manufacturers, my company – GE Aerospace – is pioneering multiple approaches to help develop such materials. We know that engines become more efficient when they burn at higher temperatures and pressures. We also know that nitrous-oxide (NOx) emissions fall when an engine burns more leanly. Unfortunately, there are no metals we know of that can survive to such high temperatures.

But the quest for unobtanium can drive innovative technical solutions. At GE, for example, we’re making progress by looking instead at composite materials, such as carbon fibre and composite matrix ceramics. Stronger and more tolerant to heat and pressure than metals, they’ve already been included on the turbofan engines in planes such as the Boeing 787 Dreamliner.

We’re also using “additive manufacturing” to build components layer by layer. This approach lets us make highly intricate components with far less waste than conventional techniques, in which a block of material is machined away. We’re also developing innovative lean-burn combustion technologies, such as novel cooling and flow strategies, to reduce NOx emissions.

While unobtanium can never be reached, it’s worth trying to get there to drive technology forward

A further example is the single crystal turbine blade developed by Rolls-Royce in 2012. Each blade is cast to form a single crystal of super alloy, making it extremely strong and able to resist the intense heat inside a jet engine. According to the company, the single crystal turbine blades operate up to 200 degrees above the melting point of their alloy. So while unobtanium can never be reached, it’s worth trying to get there to drive technology forward.

Lead us not into temptation

Now, here’s the caveat. There’s an unwelcome side to overselling, which is that it can easily morph into downright mis-selling. This was amply demonstrated by the Volkswagen diesel emissions scandal, which saw the German carmaker install “defeat devices” in its diesel engines. The software changed how the engine performed when it was undergoing emissions tests to make its NOx emissions levels appear much lower than they really were.

VW was essentially falsifying its diesel engine emissions to conform with international standards. After regulators worldwide began investigating the company, VW took a huge reputational and financial hit, ultimately costing it more than $33bn in fines, penalties and financial settlements. Senior chiefs at the company got the sack and the company’s reputation took a serious hit.

It’s tempting – and sometimes even fun – to oversell. Stretching the truth draws interest from customers and consumers. But when your product no longer does “what it says on the tin”, your brand can suffer, probably more so than having something slightly less functional.

On the upside, the quest for unobtanium and, to some extent, the selling of vapourware can drive technical progress and lead to better technical solutions. I suspect this was the case for Google Glass. The underlying technology has had some success in certain niche applications such as medical surgery and manufacturing. So even though Google Glass didn’t succeed, it did create a gap for other vendors to fill.

Google Glass was essentially a portable technology with similar functionality to smartphones, such as wireless Internet access and GPS connectivity. Customers, however, proved to be happier carrying this kind of technology in their hands than wearing it on their heads. The smartphone took off; Google Glass didn’t. But the underlying tech – touchpads, cameras, displays, processors and so on – got diverted into other products.

Vapourware, in other words, can give a firm a competitive edge while it waits for its product to mature. Who knows, maybe one day even Google Glass will make a comeback?

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By adapting their quantum twisting microscope to operate at cryogenic temperatures, researchers have made the first observations of a type of phonon that occurs in twisted bilayer graphene.  These “phasons” could have implications for the electron dynamics in these materials.

Graphene is a layer of carbon just one atom thick and it has range of fascinating and useful properties – as do bilayer and multilayer versions of graphene. Since 2018, condensed-matter physicists have been captivated by the intriguing electron behaviour in two layers of graphene that are rotated with respect to each other.

As the twist angle deviates from zero, the bilayer becomes a moiré superlattice. The emergence of this structure influences electronic properties of the material, which can transform from a semiconductor to a superconductor.

In 2023, researchers led by Shahal Ilani at the Weizmann Institute of Science in Israel developed a quantum twisting microscope to study these effects. Based on a scanning probe microscope with graphene on the substrate and folded over the tip such as to give it a flat end, the instrument allows precise control over the relative orientation between two graphene surfaces – in particular, the twist angle.

Strange metals

Now Ilani and an international team have operated the microscope at cryogenic temperatures for the first time. So far, their measurements support the current understanding of how electrons couple to phasons, which are specific modes of phonons (quantized lattice vibrations). Characterizing this coupling could help us understand “strange metals”, whose electrical resistance increases at lower temperatures – which is the opposite of normal metals.

There are different types of phonons, such as acoustic phonons where atoms within the same unit cell oscillate in phase with each other, and optical phonons where they oscillate out of phase. Phasons are phonons involving lattice oscillations in one layer that are out of phase or antisymmetric with oscillations in the layer above.

“This is the one that turns out to be very important for how the electrons behave between the layers because even a small relative displacement between the two layers affects how the electrons go from one layer to the other,” explains Weizmann’s John Birkbeck as he describes the role of phasons in twisted bilayer graphene materials.

For most phonons the coupling to electrons is weaker the lower the energy of the phonon mode. However for twisted bilayer materials, theory suggests that phason coupling to electrons increases as the twist between the two layers approaches alignment due to the antisymmetric motion of the two layers and the heightened sensitivity of interlayer tunnelling to small relative displacements.

Unique perspective

“There are not that many tools to see phonons, particularly in moiré systems” adds Birkbeck. This is where the quantum twisting microscope offers a unique perspective. Thanks to the atomically flat end of the tip, electrons can tunnel between the layer on the substrate and the layer on the tip whenever there is a matching state in terms of not just energy but also momentum too.

Where there is a momentum mismatch, tunnelling between tip and substrate is still possible by balancing the mismatch with the emission or absorption of a phonon. By operating at cryogenic temperatures, the researchers were able to get a measure of these momentum transactions and probe the electron phonon coupling too.

“What was interesting from this work is not only that we could image the phonon dispersion, but also we can quantify it,” says Birkbeck stressing the absolute nature of these quantified electron phonon coupling-strength measurements.

The measurements are the first observations of phasons in twisted bilayer graphene and reveal a strong increase in coupling as the layers approach alignment, as predicted by theory. However, the researchers were not able to study angles smaller than 6°. Below this angle the tunnelling resistance is so low that the contact resistance starts to warp readings, among other limiting factors.

Navigating without eyes

A certain amount of technical adjustment was needed to operate the tool at cryogenic temperatures, not least to “to navigate without eyes” because the team was not able to incorporate their usual optics with the cryogenic set up. The researchers hope that with further technical adjustments they will be able to use the quantum twisting microscope in cryogenic conditions at the magic angle of 1.1°, where superconductivity occurs.

Pablo Jarillo Herrero, who led the team at MIT that first reported superconductivity in twisted bilayer graphene in 2018 but was not involved in this research describes it as an “interesting study” adding, “I’m looking forward to seeing more interesting results from low temperature QTM research!”

Hector Ochoa De Eguileor Romillo at Columbia University in the US, who proposed a role for phason–electron interactions in these materials in 2019, but was also not involved in this research describes it as “a beautiful experiment”. He adds, “I think it is fair to say that this is the most exciting experimental technique of the last 15 years or so in condensed matter physics; new interesting data are surely coming.”

The research is described in Nature.

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Roses have been cultivated for thousands of years, admired for their beauty. Despite their use in fragrance, skincare and even in teas and jams, there are some things, however, that we still don’t know about these symbolic flowers.

And that includes the physical mechanism behind the shape of rose petals.

The curves and curls of leaves and flower petals arise due to the interplay between their natural growth and geometry.

Uneven growth in a flat sheet, in which the edges grow quicker than the interior, gives rise to strain and in plant leaves and petals, for example, this can result in a variety of shapes such as saddle and ripple shapes.

Yet when it comes to rose petals, the sharply pointed cusps – a point where two curves meet — that form at the edge of the petals set it apart from soft, wavy patterns seen in many other plants.

While young rose petals have smooth edges, as the rose matures the petals change to a polygonal shape with multiples cusps.

To investigate this intriguing difference, researchers from The Hebrew University of Jerusalem carried out theoretical modelling and conducted a series of experiments with synthetic disc “petals”.

They found that the pointed cusps that form at the edge of rose petals are due to a type of geometric frustration called a Mainardi-Codazzi-Peterson (MCP) incompatibility.

This type of mechanism results in stress concentrating in a specific area, which go on to form cusps to avoid tearing or forming unnatural folding.

When the researchers supressed the formation of cusps, they found that the discs reverted to being smooth and concave.

The researchers say that the findings could be used for applications in soft robotics and even the deployment of spacecraft components.

And it also goes some way to deepen our appreciation of nature’s ability to juggle growth and geometry.

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Physicists have observed axion quasiparticles for the first time in a two-dimensional quantum material. As well as having applications in materials science, the discovery could aid the search for fundamental axions, which are a promising (but so far hypothetical) candidate for the unseen dark matter pervading our universe.

Theorists first proposed axions in the 1970s as a way of solving a puzzle involving the strong nuclear force and charge-parity (CP) symmetry. In systems that obey this symmetry, the laws of physics are the same for a particle and the spatial mirror image of its oppositely charged antiparticle. Weak interactions are known to violate CP symmetry, and the theory of quantum chromodynamics (QCD) allows strong interactions to do so, too. However, no-one has ever seen evidence of this happening, and the so-called “strong CP problem” remains unresolved.

More recently, the axion has attracted attention as a potential constituent of dark matter – the mysterious substance that appears to make up more than 85% of matter in the universe. Axions are an attractive dark matter candidate because while they do have mass, and theory predicts that the Big Bang should have generated them in large numbers, they are much less massive than electrons, and they carry no charge. This combination means that axions interact only very weakly with matter and electromagnetic radiation – exactly the behaviour we expect to see from dark matter.

Despite many searches, though, axions have never been detected directly. Now, however, a team of physicists led by Jianxiang Qiu of Harvard University has proposed a new detection strategy based on quasiparticles that are axions’ condensed-matter analogue. According to Qiu and colleagues, these quasiparticle axions, as they are known, could serve as axion “simulators”, and might offer a route to detecting dark matter in quantum materials.

Topological antiferromagnet

To detect axion quasiparticles, the Harvard team constructed gated electronic devices made from several two-dimensional layers of manganese bismuth telluride (MnBi₂Te₄). This material is a rare example of a topological antiferromagnet – that is, a material that is insulating in its bulk while conducting electricity on its surface, and that has magnetic moments that point in opposite directions. These properties allow quasiparticles known as magnons (collective oscillations of spin magnetic moments) to appear in and travel through the MnBi₂Te₄. Two types of magnon mode are possible: one in which the spins oscillate in sync; and another in which they are out of phase.

Qiu and colleagues applied a static magnetic field across the plane of their MnBi₂Te₄ sheets and bombarded the devices with sub-picosecond light pulses from a laser. This technique, known as ultrafast pump-probe spectroscopy, allowed them to observe the 44 GHz coherent oscillation of the so-called condensed-matter field. This field is the CP-violating term in QCD, and it is proportional to a material’s magnetoelectric coupling constant. “This is uniquely enabled by the out-of-phase magnon in this topological material,” explains Qiu. “Such coherent oscillations are the smoking-gun evidence for the axion quasiparticle and it is the combination of topology and magnetism in MnBi₂Te₄ that gives rise to it.”

A laboratory for axion studies

Now that they have detected axion quasiparticles, Qiu and colleagues say their next step will be to do experiments that involve hybridizing them with particles such as photons. Such experiments would create a new type of “axion-polariton” that would couple to a magnetic field in a unique way – something that could be useful for applications in ultrafast antiferromagnetic spintronics, in which spin-polarized currents can be controlled with an electric field.

The axion quasiparticle could also be used to build an axion dark matter detector. According to the team’s estimates, the detection frequency for the quasiparticle is in the milli-electronvolt (meV) range. While several theories for the axion predict that it could have a mass in this range, most existing laboratory detectors and astrophysical observations search for masses outside this window.

“The main technical barrier to building such a detector would be grow high-quality large crystals of MnBi₂Te₄ to maximize sensitivity,” Qiu tells Physics World. “In contrast to other high-energy experiments, such a detector would not require expensive accelerators or giant magnets, but it will require extensive materials engineering.”

The research is described in Nature.

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This episode of the Physics World Weekly podcast features the Nobel laureate Ferenc Krausz. He is director of the Max-Planck Institute of Quantum Optics and a professor at LMU Munich, both in Germany, and CEO and scientific director of the Center for Molecular Fingerprinting in Budapest, Hungary.

In a conversation with Physics World’s Tami Freeman Krausz talks about his research into using ultrashort-pulsed laser technology to develop a diagnostic tool for early disease detection. He also discusses his collaboration with Semmelweis University to establish the John von Neumann Institute for Data Science, and describes the Science4People initiative, a charity that he and his colleagues founded to provide education for children who have been displaced by the war in Ukraine.

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Researchers at Linköping University in Sweden have developed a new fluid electrode and used it to make a soft, malleable battery that can recharge and discharge over 500 cycles while maintaining its high performance. The device, which continues to function even when stretched to twice its length, might be used in next-generation wearable electronics.

Futuristic wearables such as e-skin patches, e-textiles and even internal e-implants on the organs or nerves will need to conform far more closely to the contours of the human body than today’s devices can. To fulfil this requirement of being soft and stretchable as well as flexible, such devices will need to be made from mechanically pliant components powered by soft, supple batteries. Today’s batteries, however, are mostly rigid. They also tend to be bulky because long-term operations and power-hungry functions such as wireless data transfer, continuous sensing and complex processing demand plenty of stored energy.

To overcome these barriers, researchers led by the Linköping chemist Aiman Rahmanudin decided to rethink the very concept of battery electrode design. Instead of engineering softness and stretchability into a solid electrode, as was the case in most previous efforts, they made the electrode out of a fluid. “Bulky batteries compromise the mechanical compliance of wearable devices, but since fluids can be easily shaped into any configuration, this limitation is removed, opening up new design possibilities for next-generation wearables,” Rahmanudin says.

A “holistic approach”

Designing a stretchable battery requires a holistic approach, he adds, as all the device’s components need to be soft and stretchy. For example, they used a modified version of the wood-based biopolymer lignin as the cathode and a conjugated poly(1-amino-5-chloroanthraquinone) (PACA) as the anode. They made these electrodes fluid by dispersing them separately with conductive carbon fillers in an aqueous electrolyte medium consisting of 0.1 M HClO₄.

To integrate these electrodes into a complete cell, they had to design a stretchable current collector and an ion-selective membrane to prevent the cathodic and anodic fluids from crossing over. They also encapsulated the fluids in a robust, low-permeability elastomer to prevent them from drying up.

Designing energy storage devices from the “inside out”

Previous flexible, high-performance electrode work by the Linköping team focused on engineering the mechanical properties of solid battery electrodes by varying their Young’s modulus. “For example, think of a rubber composite that can be stretched and bent,” explains Rahmanudin. “The thicker the rubber, however, the higher the force required to stretch it, which affects mechanical compliancy.

“Learning from our past experience and work on electrofluids (which are conductive particles dispersed in a liquid medium employed as stretchable conductors), we figured that mixing redox particles with conductive particles and suspending them in an electrolyte could potentially work as battery electrodes. And we found that it did.”

Rahmanudin tells Physics World that fluid-based electrodes could lead to entirely new battery designs, including batteries that could be moulded into textiles, embedded in skin-worn patches or integrated into soft robotics.

After reporting their work in Science Advances, the researchers are now working on increasing the voltage output of their battery, which currently stands 0.9 V. “We are also looking into using Earth-abundant and sustainable materials like zinc and manganese oxide for future versions of our device and aim at replacing the acidic electrolyte we used with a safer pH neutral and biocompatible equivalent,” Rahmanudin says.

Another exciting direction, he adds, will be to exploit the fluid nature of such materials to build batteries with more complex three-dimensional shapes, such as spirals or lattices, that are tailored for specific applications. “Since the electrodes can be poured, moulded or reconfigured, we envisage a lot of creative potential here,” Rahmanudin says.

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The first strong evidence for an exoplanet with an orbit perpendicular to that of the binary system it orbits has been observed by astronomers in the UK and Portugal. Based on observations from the ESO’s Very Large Telescope (VLT), researchers led by Tom Baycroft, a PhD student at the University of Birmingham, suggest that such an exoplanet is required to explain the changing orientation in the orbit of a pair of brown dwarfs – objects that are intermediate in mass between the heaviest gas-giant planets and the lightest stars.

The Milky Way is known to host a diverse array of planetary systems, providing astronomers with extensive insights into how planets form and systems evolve. One thing that is evident is that most exoplanets (planets that orbit stars other than the Sun) and systems that have been observed so far bear little resemblance to Earth and the solar system.

Among the most interesting planets are the circumbinaries, which orbit two stars in a binary system. So far, 16 of these planets have been discovered. In each case, they have been found to orbit in the same plane as the orbits of their binary host stars. In other words, the planetary system is flat. This is much like the solar system, where each planet orbits the Sun within the same plane.

“But there has been evidence that planets might exist in a different configuration around a binary star,” Baycroft explains. “Inclined at 90° to the binary, these polar orbiting planets have been theorized to exist, and discs of dust and gas have been found in this configuration.”

Especially interesting

Baycroft’s team had set out to investigate a binary pair of brown dwarfs around 120 light–years away. The system is called 2M1510 and each brown dwarf is only about 45 million years old and they have masses about 18 times that of Jupiter. The pair are especially interesting because they are eclipsing: periodically passing in front of each other from our line of sight. When observed by the VLT, this unique vantage allowed the astronomers to determine the masses and radii of the stars and the nature of their orbit.

“This is a rare object, one of only two eclipsing binary brown dwarfs, which is useful for understanding how brown dwarfs form and evolve,” Baycroft explains. “In our study, we were not looking for a planet, only aiming to improve our understanding of the brown dwarfs.”

Yet as they analysed the VLT’s data, the team noticed something strange about pair’s orbit. Doppler shifts in the light they emitted revealed that their elliptical orbit was slowly changing orientation in an apsidal precession.

Not unheard of

This behaviour is not unheard of. In its orbit around the Sun, Mercury undergoes apsidal precession, which is explained by Albert Einstein’s general theory of relativity. But Baycroft says that the precession must have had an entirely different cause in the brown-dwarf pair.

“Unlike Mercury, this precession is going backwards, in the opposite direction to the orbit,” he explains. “Ruling out any other causes for this, we find that the best explanation is that there is a companion to the binary on a polar orbit, inclined at close to 90° relative to the binary.” As it exerts its gravitational pull on the binary pair, the inclination of this third, smaller body induces a gradual rotation in the orientation of the binary’s elliptical orbit.

For now, the characteristics of this planet are difficult to pin down and the team believe its mass could lie anywhere between 10–100 Earths. All the same, the astronomers are confident that their results now confirm the possibility of polar exoplanets existing in circumbinary orbits – providing valuable guidance for future observations.

“This result exemplifies how the many different configurations of planetary systems continue to astound us,” Baycroft comments. “It also paves the way for more studies aiming to find out how common such polar orbits may be.”

The observations are described in Science Advances.

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Researchers in Singapore and the US have independently developed two new types of photonic computer chips that match existing purely electronic chips in terms of their raw performance. The chips, which can be integrated with conventional silicon electronics, could find use in energy-hungry technologies such as artificial intelligence (AI).

For nearly 60 years, the development of electronic computers proceeded according to two rules of thumb: Moore’s law (which states that the number of transistors in an integrated circuit doubles every two years) and Dennard scaling (which says that as the size of transistors decreases, their power density will stay constant). However, both rules have begun to fail, even as AI systems such as large language models, reinforcement learning and convolutional neural networks are becoming more complex. Consequently, electronic computers are struggling to keep up.

Light-based computation, which exploits photons instead of electrons, is a promising alternative because it can perform multiplication and accumulation (MAC) much more quickly and efficiently than electronic devices. These operations are crucial for AI, and especially for neural networks. However, while photonic systems such as photonic accelerators and processors have made considerable progress in performing linear algebra operations such as matrix multiplication, integrating them into conventional electronics hardware has proved difficult.

A hybrid photonic-electronic system

The Singapore device was made by researchers at the photonic computing firm Lightelligence and is called PACE, for Photonic Arithmetic Computing Engine. It is a hybrid photonic-electronic system made up of more than 16 000 photonic components integrated on a single silicon chip and performs matrix MAC on 64-entry binary vectors.

“The input vector data elements start in electronic form and are encoded as binary intensities of light (dark or light) and fed into a 64 x 64 array of optical weight modulators that then perform multiply and summing operations to accumulate the results,” explains Maurice Steinman, Lightelligence’s senior vice president and general manager for product strategy. “The result vectors are then converted back to the electronic domain where each element is compared to its corresponding programmable 8-bit threshold, producing new binary vectors that subsequently re-circulate optically through the system.”

The process repeats until the resultant vectors reach “convergence” with settled values, Steinman tells Physics World. Each recurrent step requires only a few nanoseconds and the entire process completes quickly.

The Lightelligence device, which the team describe in Nature, can solve complex computational problems known as max-cut/optimization problems that are important for applications in areas such as logistics. Notably, its greatly reduced minimum latency – a key measure of computation speed – means it can solve a type of problem known as an Ising model in just five nanoseconds. This makes it 500 times faster than today’s best graphical-processing-unit-based systems at this task.

High level of integration achieved

Independently, researchers led by Nicholas Harris at Lightmatter in Mountain View, California, have fabricated the first photonic processor capable of executing state-of-the-art neural network tasks such as classification, segmentation and running reinforcement learning algorithms. Lightmatter’s design consists of six chips in a single package with high-speed interconnects between vertically aligned photonic tensor cores (PTCs) and control dies. The team’s processor integrates four 128 x 128 PTCs, with each PTC occupying an area of 14 x 24.96 mm. It contains all the photonic components and analogue mixed-signal circuits required to operate and members of the team say that the current architecture could be scaled to 512 x 512 computing units in a single die.

The result is a device that can perform 65.5 trillion adaptive block floating-point 35 (ABFP) 16-bit operations per second with just 78 W of electrical power and 1.6 W of optical power. Writing in Nature, the researchers claim that this represents the highest level of integration achieved in photonic processing.

The team also showed that the Lightmatter processor can implement complex AI models such as the neural network ResNet (used for image processing) and the natural language processing model BERT (short for Bidirectional Encoder Representations from Transformers) – all with an accuracy rivalling that of standard electronic processors. It can also compute reinforcement learning algorithms such as DeepMind’s Atari. Harris and colleagues have already applied their device to several real-world AI applications, such as generating literary texts and classifying film reviews, and they say that their photonic processor marks an essential step in post-transistor computing.

Both teams fabricated their photonic and electronic chips using standard complementary metal-oxide-semiconductor (CMOS) processing techniques. This means that existing infrastructures could be exploited to scale up their manufacture. Another advantage: both systems were fully integrated in a standard chip interface – a first.

Given these results, Steinman says he expects to see innovations emerging from algorithm developers who seek to exploit the unique advantages of photonic computing, including low latency. “This could benefit the exploration of new computing models, system architectures and applications based on large-scale integrated photonics circuits.”

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In his debut book, Einstein’s Tutor: the Story of Emmy Noether and the Invention of Modern Physics, Lee Phillips champions the life and work of German mathematician Emmy Noether (1882–1935). Despite living a life filled with obstacles, injustices and discrimination as a Jewish mathematician, Noether revolutionized the field and discovered “the single most profound result in all of physics”. Phillips’ book weaves the story of her extraordinary life around the central subject of “Noether’s theorem”, which itself sits at the heart of a fascinating era in the development of modern theoretical physics.

Noether grew up at a time when women had few rights. Unable to officially register as a student, she was instead able to audit courses at the University of Erlangen in Bavaria, with the support of her father who was a mathematics professor there. At the time, young Noether was one of only two female auditors in the university of 986 students. Just two years previously, the university faculty had declared that mixed-sex education would “overthrow academic order”. Despite going against this formidable status quo, she was able to graduate in 1903.

Noether continued her pursuit of advanced mathematics, travelling to the “[world’s] centre of mathematics” – the University of Göttingen. Here, she was able to sit in the lectures of some of the brightest mathematical minds of the time – Karl Schwarzschild, Hermann Minkowski, Otto Blumenthal, Felix Klein and David Hilbert. While there, the law finally changed: women were, at last, allowed to enrol as students at university. In 1904 Noether returned to the University of Erlangen to complete her postgraduate dissertation under the supervision of Paul Gordan. At the time, she was the only woman to matriculate alongside 46 men.

Despite being more than qualified, Noether was unable to secure a university position after graduating from her PhD in 1907. Instead, she worked unpaid for almost a decade – teaching her father’s courses and supervising his PhD students. As of 1915, Noether was the only woman in the whole of Europe with a PhD in mathematics. She had worked hard to be recognized as an expert on symmetry and invariant theory, and eventually accepted an invitation from Klein and Hilbert to work alongside them in Göttingen. Here, the three of them would meet Albert Einstein to discuss his latest project – a general theory of relativity.

Infiltrating the boys’ club

In Einstein’s Tutor, Phillips paints an especially vivid picture of Noether’s life at Göttingen, among colleagues including Klein, Hilbert and Einstein, who loom large and bring a richness to the story. Indeed, much of the first three chapters are dedicated to these men, setting the scene for Noether’s arrival in Göttingen. Phillips makes it easy to imagine these exceptionally talented and somewhat eccentric individuals working at the forefront of mathematics and theoretical physics together. And it was here, when supporting Einstein with the development of general relativity (GR), that Noether discovered a profound result: for every symmetry in the universe, there is a corresponding conservation law.

Throughout the book, Phillips makes the case that, without Noether, Einstein would never have been able to get to the heart of GR. Einstein himself “expressed wonderment at what happened to his equations in her hands, how he never imagined that things could be expressed with such elegance and generality”. Phillips argues that Einstein should not be credited as the sole architect of GR. Indeed, the contributions of Grossman, Klein, Besso, Hilbert, and crucially, Noether, remain largely unacknowledged – a wrong that Phillips is trying to right with this book.

Phillips makes the case that, without Noether, Einstein would never have been able to get to the heart of general relativity

A key theme running through Einstein’s Tutor is the importance of the support and allyship that Noether received from her male contemporaries. While at Göttingen, there was a battle to allow Noether to receive her habilitation (eligibility for tenure). Many argued in her favour but considered her an exception, and believed that in general, women were not suited as university professors. Hilbert, in contrast, saw her sex as irrelevant (famously declaring “this is not a bath house”) and pointed out that science requires the best people, of which she was one. Einstein also fought for her on the basis of equal rights for women.

Eventually, in 1919 Noether was allowed to habilitate (as an exception to the rule) and was promoted to professor in 1922. However, she was still not paid for her work. In fact, her promotion came with the specific condition that she remained unpaid, making it clear that Noether “would not be granted any form of authority over any male employee”. Hilbert however, managed to secure a contract with a small salary for her from the university administration.

Her allies rose to the cause again in 1933, when Noether was one of the first Jewish academics to be dismissed under the Nazi regime. After her expulsion, German mathematician Helmut Hasse convinced 14 other colleagues to write letters advocating for her importance, asking that she be allowed to continue as a teacher to a small group of advanced students – the government denied this request.

When the time came to leave Germany, many colleagues wrote testimonials in her support for immigration, with one writing “She is one of the 10 or 12 leading mathematicians of the present generation in the entire world.” Rather than being placed at a prestigious university or research institute (Hermann Weyl and Einstein were both placed at “the men’s university”, the Institute for Advanced Study in Princeton), it was recommended she join Bryn Mawr, a women’s college in Pennsylvania, US. Her position there would “compete with no-one… the most distinguished feminine mathematician connected with the most distinguished feminine university”. Phillips makes clear his distaste for the phrasing of this recommendation. However, all accounts show that she was happy at Bryn Mawr and stayed there until her unexpected death in 1935 at the age of 53.

Noether’s legacy

With a PhD in theoretical physics, Phillips has worked for many years in both academia and industry. His background shows itself clearly in some unusual writing choices. While his writing style is relaxed and conversational, it includes the occasional academic turn of phrase (e.g. “In this chapter I will explain…”), which feels out of place in a popular-science book. He also has a habit of piling repetitive and overly sincere praise onto Noether. I personally prefer stories that adopt the “show, don’t tell” approach – her abilities speak for themselves, so it should be easy to let the reader come to their own conclusions.

Phillips has made the ambitious choice to write a popular-science book about complex mathematical concepts such as symmetries and conservation laws that are challenging to explain, especially to general readers. He does his best to describe the mathematics and physics behind some of the key concepts around Noether’s theorem. However, in places, you do need to have some familiarity with university-level physics and maths to properly follow his explanations. The book also includes a 40-page appendix filled with additional physics content, which I found unnecessary.

Einstein’s Tutor does achieve its primary goal of familiarizing the reader with Emmy Noether and the tremendous significance of her work. The final chapter on her legacy breezes quickly through developments in particle physics, astrophysics, quantum computers, economics and XKCD Comics to highlight the range and impact this single theorem has had. Phillips’ goal was to take Noether into the mainstream, and this book is a small step in the right direction. As cosmologist and author Katie Mack summarizes perfectly: “Noether’s theorem is to theoretical physics what natural selection is to biology.”

• 2024 Hachette UK £25hb 368pp

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In this episode of Physics World Stories, writer Kevlin Henney discusses his new flash fiction, Heisenberg (not) in Helgoland – written exclusively for Physics World as part of the International Year of Quantum Science and Technology. The story spans two worlds: the one we know, and an alternate reality in which Werner Heisenberg never visits the island of Helgoland – a trip that played a key role in the development of quantum theory.

Henney reads an extract from the piece and reflects on the power of flash fiction – why the format’s brevity and clarity make it an interesting space for exploring complex ideas. In conversation with host Andrew Glester, he also discusses his varied career as an independent software consultant, trainer and writer. Tune in to hear his thoughts on quantum computing, and why there should be greater appreciation for how modern physics underpins the technologies we use every day.

The full version of Henney’s story will be published in the Physics World Quantum Briefing 2025 – a free-to-read digital issue launching in May. Packed with features on the history, mystery and applications of quantum mechanics, it will be available via the Physics World website.

The image accompanying this article is Werner Heisenberg in 1933 (Credit: German Federal Archive with posterised version by James Dacey/Physics World) CC-BY-SA 3.0

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Sending an email, typing a text message, streaming a movie. Many of us do these activities every day. But what if you couldn’t move your muscles and navigate the digital world? This is where brain–computer interfaces (BCIs) come in.

BCIs that are implanted in the brain can bypass pathways damaged by illness and injury. They analyse neural signals and produce an output for the user, such as interacting with a computer.

A major focus for scientists developing BCIs has been to interpret brain activity associated with movements to control a computer cursor. The user drives the BCI by imagining arm and hand movements, which often originate in the dorsal motor cortex. Speech BCIs, which restore communication by decoding attempted speech from neural activity in sensorimotor cortical areas such as the ventral precentral gyrus, have also been developed.

Researchers at the University of California, Davis recently found that the same part of the brain that supported a speech BCI could also support computer cursor control for an individual with amyotrophic lateral sclerosis (ALS). ALS is progressive neurodegenerative disease affecting the motor neurons in the brain and spinal cord.

“Once that capability [to control a computer mouse] became reliably achievable roughly a decade ago, it stood to reason that we should go after another big challenge, restoring speech, that would help people unable to speak. And from there – and this is where this new paper comes in – we recognized that patients would benefit from both of these capabilities [speech and computer cursor control],” says Sergey Stavisky, who co-directs the UC Davis Neuroprosthetics Lab with David Brandman.

Their clinical case study suggests that computer cursor control may not be as body-part-specific as scientists previously believed. If results are replicable, this could enable the creation of multi-modal BCIs that restore communication and movement to people with paralysis. The researchers share information about their cursor BCI and the case study in the Journal of Neural Engineering.

The study participant, a 45-year-old man with ALS, had previous success working with a speech BCI. The researchers recorded neural activity from the participant’s ventral precentral gyrus while he imagined controlling a computer cursor, and built a BCI to interpret that neural activity and predict where and when he wanted to move and click the cursor. The participant then used the new cursor BCI to send texts and emails, watch Netflix, and play The New York Times Spelling Bee game on his personal computer.

“This finding, that the tiny region of the brain we record from has a lot more than just speech information, has led to the participant also being able to control his own computer on a daily basis, and get back some independence for him and his family,” says first author Tyler Singer-Clark, a graduate student in biomedical engineering at UC Davis.

The researchers found that most of the information driving cursor control came from one of the participant’s four implanted microelectrode arrays, while click information was available on all four of the BCI arrays.

“The neural recording arrays are the same ones used in many prior studies,” explains Singer-Clark. “The result that our cursor BCI worked well given this choice makes it all the more convincing that this brain area (speech motor cortex) has untapped potential for controlling BCIs in multiple useful ways.”

The researchers are working to incorporate more computer actions into their cursor BCI, to make the control faster and more accurate, and to reduce calibration time. They also note that it’s important to replicate these results in more people to understand how generalizable the results of their case study may be.

The research was conducted as part of the BrainGate2 clinical trial.

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A new all-electrical way of controlling spin-polarized currents has been developed by researchers at the Singapore University of Technology and Design (SUTD). By using bilayers of recently-discovered materials known as altermagnets, the researchers developed a tuneable and magnetic-free alternative to current approaches – something they say could bring spintronics closer to real-world applications.

Spintronics stores and processes information by exploiting the quantum spin (or intrinsic angular momentum) of electrons rather than their charge. The technology works by switching electronic spins, which can point either “up” or “down”, to perform binary logical operations in much the same way as electronic circuits use electric charge. One of the main advantages is that when an electron’s spin switches direction, its new state is stored permanently; it is said to be “non-volatile”. Spintronics circuits therefore do not require any additional input power to keep their states stable, which could make them more efficient and faster than the circuits in conventional electronic devices.

The problem is that the spin currents that carry information in spintronics circuits are usually generated using ferromagnetic materials and the magnetization of these materials can only be switched using very strong magnetic fields. Doing this requires bulky apparatus, which hinders the creation of ultracompact devices – a prerequisite for real-world applications.

“Notoriously difficult to achieve”

Controlling the spins with electric fields instead would be ideal, but Ang Yee Sin, who led the new research, says it has proved notoriously difficult to achieve – until now. “We have now shown that we can generate and reverse the spin direction of the electron current in an altermagnet made of two very thin layers of chromium sulphide (CrS) at room temperature using only an electric field,” Ang says.

Altermagnets, which were only discovered in 2024, are different from the conventional magnetically-ordered materials, ferromagnets and antiferromagnets. In ferromagnets, the magnetic moments (or spins) of atoms line up parallel to each other. In antiferromagnets, they line up antiparallel. The spins in altermagnets are also antiparallel, but the atoms that host these spins are rotated with respect to their neighbours. This combination gives altermagnets some properties of both ferromagnets and antiferromagnets, plus new properties of their own.

In bilayers of CrS, explains Ang, the electrons in each layer naturally prefer to spin in opposite directions, essentially cancelling each other out. “When we apply an electric field across the layers, however, one layer becomes more ‘active’ than the other. The current flowing through the device therefore becomes spin-polarized.”

A new device concept

The main challenge the researchers faced in their work was to identify a suitable material and a stacking arrangement in which spin and layers intertwined just right. This required detailed quantum-level simulations and theoretical modelling to prove that CrS bilayers could do the job, says Ang.

The work opens up a new device concept that the team calls layer-spintronics in which spin control is achieved via layer selection using an electric field. According to Ang, this concept has clear applications for next-generation, energy-efficient, compact and magnet-free memory and logic devices. And, since the technology works at room temperature and uses electric gating – a common approach in today’s electronics – it could make it possible to integrate spintronics devices with current semiconductor technology. This could lead to novel spin transistors, reconfigurable logic gates, or ultrafast memory cells based entirely on spin in the future, he says.

The SUTD researchers, who report their work in Materials Horizons, now aim to identify other 2D altermagnets that can host similar or even more robust spin-electric effects. “We are also collaborating with experimentalists to synthesize and characterize CrS bilayers to validate our predictions in the lab and investigating how to achieve non-volatile spin control by integrating them with ferroelectric materials,” reveals Ang. “This could potentially allow for memory devices that can retain information for longer.”

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Most of us have heard of Schrödinger’s eponymous cat, but it is not the only feline in the quantum physics bestiary. Quantum Cheshire cats may not be as well known, yet their behaviour is even more insulting to our classical-world common sense.

These quantum felines get their name from the Cheshire cat in Lewis Carroll’s Alice’s Adventures in Wonderland, which disappears leaving its grin behind. As Alice says: “I’ve often seen a cat without a grin, but a grin without a cat! It’s the most curious thing I ever saw in my life!”

Things are curiouser in the quantum world, where the property of a particle seems to be in a different place from the particle itself. A photon’s polarization, for example, may exist in a totally different location from the photon itself: that’s a quantum Cheshire cat.

While the prospect of disembodied properties might seem disturbing, it’s a way of interpreting the elegant predictions of quantum mechanics. That at least was the thinking when quantum Cheshire cats were first put forward by Yakir Aharonov, Sandu Popescu, Daniel Rohrlich and Paul Skrzypczyk in an article published in 2013 (New J. Phys. 15 113015).

Strength of a measurement

To get to grips with the concept, remember that making a measurement on a quantum system will “collapse” it into one of its eigenstates – think of opening the box and finding Schrödinger’s cat either dead or alive. However, by playing on the trade-off between the strength of a measurement and the uncertainty of the result, one can gain a tiny bit of information while disturbing the system as little as possible. If such a measurement is done many times, or on an ensemble of particles, it is possible to average out the results, to obtain a precise value.

First proposed in the 1980s, this method of teasing out information from the quantum system by a series of gentle pokes is known as weak measurement. While the idea of weak measurement in itself does not appear a radical departure from quantum formalism, “an entire new world appeared” as Popescu puts it. Indeed, Aharonov and his collaborators have spent the last four decades investigating all kinds of scenarios in which weak measurement can lead to unexpected consequences, with the quantum Cheshire cat being one they stumbled upon.

In their 2013 paper, Aharonov and colleagues imagined a simple optical interferometer set-up, in which the “cat” is a photon that can be in either the left or the right arm, while the “grin” is the photon’s circular polarization. The cat (the photon) is first prepared in a certain superposition state, known as pre-selection. After it enters the set-up, the cat can leave via several possible exits. The disembodiment between particle and property appears in the cases in which the particle emerges in a particular exit (post-selection).

Certain measurements, analysing the properties of the particle, are performed while the particle is in the interferometer (in between the pre- and post-selection). Being weak measurements, they have to be carried out many times to get the average. For certain pre- and post-selection, one finds the cat will be in the left arm while the grin is in the right. It’s a Cheshire cat disembodied from its grin.

The mathematical description of this curious state of affairs was clear, but the interpretation seemed preposterous and the original article spent over a year in peer review, with its eventual publication still sparking criticism. Soon after, experiments with polarized neutrons (Nature Comms 5 4492) and photons (Phys. Rev. A 94 012102) tested the original team’s set-up. However, these experiments and subsequent tests, despite confirming the theoretical predictions, did not settle the debate – after all, the issue was with the interpretation.

A quantum of probabilities

To come to terms with this perplexing notion, think of the type of pre- and post-selected set-up as a pachinko machine, in which a ball starts at the top in a single pre-selected slot and goes down through various obstacles to end up in a specific point (post-selection): the jackpot hole. If you count how many balls hit the jackpot hole, you can calculate the probability distribution. In the classical world, measuring the position and properties of the ball at different points, say with a camera, is possible.

This observation will not affect the trajectory of the ball, or the probability of the jackpot. In a quantum version of the pachinko machine, the pre- and post-selection will work in a similar way, except you could feed in balls in superposition states. A weak measurement will not disturb the system so multiple measurements can tease out the probability of certain outcomes. The measurement result will not yield an eigenvalue, which corresponds to a physical property of the system, but weak values, and the way one should interpret these is not clear-cut.

1 Split particle property

Quantum Cheshire cats are a curious phenomenon, whereby the property of a quantum particle can be completely separate from the particle itself. A photon’s polarization, for example, may exist at a location where there is no photon at all. In this illustration, our quantum Cheshire cats (the photons) are at a pachinko parlour. Depending on certain pre- and post-selection criteria, the cats end up in one location – in one arm of the detector or the other – and their grins in a different location, on the chairs.  

To make sense of this in a quantum sense, we need an intuitive mental image, even a limited one. This is why quantum Cheshire cats are a powerful metaphor, but they are also more than that, guiding researchers into new directions. Indeed, since the initial discovery, Aharonov, Popescu and colleagues have stumbled  upon more surprises.

In 2021 they generalized the quantum Cheshire cat effect to a dynamical picture in which the “disembodied” property can propagate in space (Nature Comms 12 4770). For example, there could be a flow of angular momentum without anything carrying it (Phys. Rev. A 110 L030201). In another generalization, Aharonov imagined a massive particle with a mass that could be measured in one place with no momentum, while its momentum could be measured in another place without its mass (Quantum 8 1536). A gedankenexperiment to test this effect would involve a pair of nested Mach–Zehnder interferometers with moving mirrors and beam splitters.

Provocative interpretations

If you find these ideas bewildering, you’re in good company. “They’re brain teasers,” explains Jonte Hance, a researcher in quantum foundations at Newcastle University, UK. In fact, Hance thinks that quantum Cheshire cats are a great way to get people interested in the foundations of quantum mechanics.

Physicists were too busy applying quantum mechanics to various problems to be bothered with foundational questions

Sure, the early years of quantum physics saw famous debates between Niels Bohr and Albert Einstein, culminating in the criticism in the Einstein–Podolski–Rosen (EPR) paradox (Phys. Rev. 47 777) in 1935. But after that, physicists were too busy applying quantum mechanics to various problems to be bothered with foundational questions.

This lack of interest in quantum fundamentals is perfectly illustrated by two anecdotes, the first involving Aharonov himself. When he was studying physics at Technion in Israel in the 1950s, he asked Nathan Rosen (the R of the EPR) about working on the foundations of quantum mechanics. The topic was deemed so unfashionable that Rosen advised him to focus on applications. Luckily, Aharonov ignored the advice and went on to work with American quantum theorist David Bohm.

The other story concerns Alain Aspect, who in 1975 visited CERN physicist John Bell to ask for advice on his plans to do an experimental test of Bell’s inequalities to settle the EPR paradox. Bell’s very first question was not about the details of the experiment – but whether Aspect had a permanent position (Nature Phys. 3 674). Luckily, Aspect did, so he carried out the test, which went on to earn him a share of the 2022 Nobel Prize for Physics.

As quantum computing and quantum information began to emerge, there was a brief renaissance in quantum foundations culminating in the early 2010s. But over the past decade, with many of aspects of quantum physics reaching commercial fruition, research interest has shifted firmly once again towards applications.

Despite popular science’s constant reminder of how “weird” quantum mechanics is, physicists often take the pragmatic “shut up and calculate” approach. Hance says that researchers “tend to forget how weird quantum mechanics is, and to me you need that intuition of it being weird”. Indeed, paradoxes like Schrödinger’s cat and EPR have attracted and inspired generations of physicists and have been instrumental in the development of quantum technologies.

The point of the quantum Cheshire cat, and related paradoxes, is to challenge our intuition and provoke us to think outside the box. That’s important even if applications may not be immediately in sight. “Most people agree that although we know the basic laws of quantum mechanics, we don’t really understand what quantum mechanics is all about,” says Popescu.

Aharonov and colleagues’ programme is to develop a correct intuition that can guide us further. “We strongly believe that one can find an intuitive way of thinking about quantum mechanics,” adds Popescu. That may, or may not, involve felines.

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India must intensify its efforts in quantum technologies as well as boost private investment if it is to become a leader in the burgeoning field. That is according to the first report from India’s National Quantum Mission (NQM), which also warns that the country must improve its quantum security and regulation to make its digital infrastructure quantum-safe.

Approved by the Indian government in 2023, the NQM is an eight-year $750m (60bn INR) initiative that aims to make the country a leader in quantum tech. Its new report focuses on developments in four aspects of NQM’s mission: quantum computing; communication; sensing and metrology; and materials and devices.

Entitled India’s International Technology Engagement Strategy for Quantum Science, Technology and Innovation, the report finds that India’s research interests include error-correction algorithms for quantum computers. It is also involved in building quantum hardware with superconducting circuits, trapped atoms/ions and engineered quantum dots.

The NQM-supported Bengaluru-based startup QPiAI, for example, recently developed a 25-superconducting qubit quantum computer called “Indus”, although the qubits were fabricated abroad.

Ajay Sood, principal scientific advisor to the Indian government, told Physics World that while India is strong in “software-centric, theoretical and algorithmic aspects of quantum computing, work on completely indigenous development of quantum computing hardware is…at a nascent stage.”

Sood, who is a physicist by training, adds that while there are a few groups working on different platforms, these are at less than 10-qubit stage. “[It is] important for [India] to have indigenous capabilities for fabricating qubits and other ancillary hardware for quantum computers,” he says

India is also developing secure protocols and satellite-based systems and implementing quantum systems for precision measurements. QNu Labs – another Begalaru startup – is, for example, developing a quantum-safe communication-chip module to secure satellite and drone communications with built-in quantum randomness and security micro-stack.

Lagging behind

The report highlights the need for greater involvement of Indian industry in hardware-related activities. Unlike other countries, India struggles with limited industry funding, in which most comes from angel investors, with limited participation from institutional investors such as venture-capital firms, tech corporates and private equity funds.

There are many areas of quantum tech that are simply not being pursued in India

Arindam Ghosh

The report also calls for more indigenous development of essential sensors and devices such as single-photon detectors, quantum repeaters, and associated electronics, with necessary testing facilities for quantum communication. “There is also room for becoming global manufacturers and suppliers for associated electronic or cryogenic components,” says Sood. “Our industry should take this opportunity.”

India must work on its quantum security and regulation as well, according to the report. It warns that the Indian financial sector, which is one the major drivers for quantum tech applications, “risks lagging behind” in quantum security and regulation, with limited participation of Indian financial-service providers.

“Our cyber infrastructure, especially related to our financial systems, power grids, and transport systems, need to be urgently protected by employing the existing and evolving post quantum cryptography algorithms and quantum key distribution technologies,” says Sood.

India currently has about 50 educational programmes in various universities and institutions. Yet Arindam Ghosh, who runs the Quantum Technology Initiative at the India Institute of Science, Bangalore, says that the country faces a lack of people going into quantum-related careers.

“In spite of [a] very large number of quantum-educated graduates, the human resource involved in developing quantum technologies is abysmally small,” says Ghosh. “As a result, there are many areas of quantum tech that are simply not being pursued in India.”  Other problems, according to Ghosh, include “modest” government funding compared to other countries as well as “slow and highly bureaucratic” government machinery.

Sood, however, is optimistic, pointing out recent Indian initiatives such as setting up hardware fabrication and testing facilities, supporting start-ups as well as setting up a $1.2bn (100bn INR) fund to promote “deep-tech” startups. “[With such initiatives] there is every reason to believe that India would emerge even stronger in the field,” says Sood.

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A new theoretical framework proposes that gravity may arise from entropy, offering a fresh perspective on the deep connections between geometry, quantum mechanics and statistical physics. Developed by Ginestra Bianconi, a mathematical physicist at Queen Mary University of London, UK, and published in Physical Review D, this modified version of gravity provides new quantum information theory insights on the well-established link between statistical mechanics and gravity that is rooted in the thermodynamic properties of black holes.

Quantum relative entropy

At the heart of Bianconi’s theory is the concept of quantum relative entropy (QRE). This is a fundamental concept of information theory, and it quantifies the difference in information encoded in two quantum states. More specifically, QRE is a measure of how much information of one quantum state is carried by another quantum state.

Bianconi’s idea is that the metrics associated with spacetime are quantum operators that encode the quantum state of its geometry. Building on this geometrical insight, she proposes that the action for gravity is the QRE between two different metrics: one defined by the geometry of spacetime and another by the matter fields present within it. In this sense, the theory takes inspiration from John Wheeler’s famous description of gravity: “Matter tells space how to curve, and space tells matter how to move.” However, it also goes further, as it aims to make this relationship explicit in the mathematical formulation of gravity, framing it in a statistical mechanics and information theory action.

Additionally, the theory adapts QRE to the Dirac-Kähler formalism extended to bosons, allowing for a more nuanced understanding of spacetime. The Dirac-Kähler formalism is a geometric reformulation of fermions using differential forms, unifying spinor and tensor descriptions in a coordinate-free way. In simpler terms, it offers an elegant way to describe particles like electrons using the language of geometry and calculus on manifolds.

The role of the G-field

For small energies and low values of spacetime curvature (the “low coupling” regime), the equations Bianconi presents reduce to the standard equations of Einstein’s general theory of relativity. Beyond this regime, the full modified Einstein equations can be written in terms of a new field, the G-field, that gives rise to a non-zero cosmological constant. Often associated with the accelerated expansion of the universe, the cosmological constant contributes to the still-mysterious substance known as dark energy, which is estimated to make up 68% of the mass-energy in the universe. A key feature of Bianconi’s entropy-based theory is that the cosmological constant is actually not constant, but dependent on the G-field. Hence, a key feature of the G-field is that it might provide new insight into what the cosmological constant really is, and where it comes from.

The G-field also has implications for black hole physics. In a follow-up work, Bianconi shows that a common solution in general relativity known as the Schwarzschild metric is an approximation, with the full solution requiring consideration of the G-field’s effects.

What does this mean for quantum gravity and cosmology?

The existence of a connection between black holes and entropy also raises the possibility that Bianconi’s framework could shed new light on the black hole information paradox. Since black holes are supposed to evaporate due to Hawking radiation, the paradox addresses the question of whether information that falls into a black hole is truly lost after evaporation. Namely, does a black hole destroy information forever, or is it somehow preserved?

The general theory predicts that the QRE for the Schwarzschild black hole follows the area law, a key feature of black hole thermodynamics, suggesting that further exploration of this framework might lead to new answers about the fundamental nature of black holes.

Unlike other approaches to quantum gravity that are primarily phenomenological, Bianconi’s framework seeks to understand gravity from first principles by linking it directly to quantum information and statistical mechanics. When asked how she became interested in this line of research, she emphasizes the continuity between her previous work on the topology and geometry of higher-order networks, her work on the topological Dirac operator and her current pursuits.

“I was especially struck by a passage in Gian Francesco Giudice’s recent book Before the Big Bang, where a small girl asks, ‘If your book speaks about the universe, does it also speak about me?’” Bianconi says. “This encapsulates the idea that new bridges between different scientific domains could be key to advancing our understanding.”

Future directions

There is still much to explore in this approach. In particular, Bianconi hopes to extend this theory into second quantization, where fields are thought of as operators just as physical quantities (position, momentum, so on) are in first quantization. Additionally, the modified Einstein equations derived in this theory have yet to be fully solved, and understanding the full implications of the theory for classical gravity is an ongoing challenge.

Though the research is still in its early stages, Bianconi emphasizes that it could eventually lead to testable hypotheses. The relationship between the theory’s predicted cosmological constant and experimental measurements, for example, could offer a way to test it against existing data.

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Vaire Computing is a start-up seeking to commercialize computer chips based on the principles of reversible computing – a topic Earley studied during her PhD in applied mathematics and theoretical physics at the University of Cambridge, UK. The central idea behind reversible computing is that reversible operations use much less energy, and thus generate much less waste heat, than those in conventional computers.

What skills do you use every day in your job?

In an early-stage start-up environment, you have to wear lots of different hats. Right now, I’m planning for the next few years, but I’m also very deep into the engineering side of Vaire, which spans a lot of different areas.

The skill I use most is my ability to jump into a new field and get up to speed with it as quickly as possible, because I cannot claim to be an expert in all the different areas we work in. I cannot be an expert in integrated circuit design as well as developing electronic design automation tooling as well as building better resonators. But what I can do is try to learn about all these things at as deep a level as I can, very quickly, and then guide the people around me with higher-level decisions while also having a bit of fun and actually doing some engineering work.

What do you like best and least about your job?

We have so many great people at Vaire, and being able to talk with them and discuss all the most interesting aspects of their specialities is probably the part I like best. But I’m also enjoying the fact that in a few years, all this work will culminate in an actual product based on things I worked on when I was in academia. I love theory, and I love thinking about what could be possible in hundreds of years’ time, but seeing an idea get closer and closer to reality is great.

The part I have more of a love-hate relationship with is just how intense this job is. I’m probably intrinsically a workaholic. I don’t think I’ve ever had a good balance in terms of how much time I spend on work, whether now or when I was doing my PhD or even before. But when you are responsible for making your company succeed, that degree of intensity becomes unavoidable. It feels difficult to take breaks or to feel comfortable taking breaks, but I hope that as our company grows and gets more structured, that part will improve.

What do you know now that you wish you’d known when you were starting out in your career?

There are so many specifics of what it means to build a computer chip that I wish I’d known. I may even have suffered a little bit from the Dunning–Kruger effect [in which people with limited experience of a particular topic overestimate their knowledge] at the beginning, thinking, “I know what a transistor is like. How hard can it be to build a large-scale integrated circuit?”

It turns out it’s very, very hard, and there’s a lot of complexity around it. When I was a PhD student, it felt like there wasn’t that big a gap between theory and implementation. But there is, and while to some extent it’s not possible to know about something until you’ve done it, I wish I’d known a lot more about chip design a few years ago.

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