Popularity isn’t everything. But it is something, so for the second year running, we’re finishing our trip around the Sun by looking back at the physics stories that got the most attention over the past 12 months. Here, in ascending order of popularity, are the 10 most-read stories published on the Physics World website in 2025.

10. Quantum on the brain

We’ve had quantum science on our minds all year long, courtesy of 2025 being UNESCO’s International Year of Quantum Science and Technology. But according to theoretical work by Partha Ghose and Dimitris Pinotsis, it’s possible that the internal workings of our brains could also literally be driven by quantum processes.

Though neurons are generally regarded as too big to display quantum effects, Ghose and Pinotsis established that the equations describing the classical physics of brain responses are mathematically equivalent to the equations describing quantum mechanics. They also derived a Schrödinger-like equation specifically for neurons. So if you’re struggling to wrap your head around complex quantum concepts, take heart: it’s possible that your brain is ahead of you.

9. Could an extra time dimension reconcile quantum entanglement with local causality?

Einstein famously disliked the idea of quantum entanglement, dismissing its effects as “spooky action at a distance”. But would he have liked the idea of an extra time dimension any better? We’re not sure he would, but that is the solution proposed by theoretical physicist Marco Pettini, who suggests that wavefunction collapse could propagate through a second time dimension. Pettini got the idea from discussions with the Nobel laureate Roger Penrose and from reading old papers by David Bohm, but not everyone is impressed by these distinguished intellectual antecedents. In this article, Bohm’s former student and frequent collaborator Jeffrey Bub went on the record to say he “wouldn’t put any money on” Pettini’s theory being correct. Ouch.

8. And now for something completely different

Continuing the theme of intriguing, blue-sky theoretical research, the eighth-most-read article of 2025 describes how two theoretical physicists, Kaden Hazzard and Zhiyuan Wang, proposed a new class of quasiparticles called paraparticles. Based on their calculations, these paraparticles exhibit quantum properties that are fundamentally different from those of bosons and fermions. Notably, paraparticles strikes a balance between the exclusivity of fermions and the clustering tendency of bosons, with up to two paraparticles allowed to occupy the same quantum state (rather than zero for fermions or infinitely many for bosons). But do they really exist? No-one knows yet, but Hazzard and Wang say that experimental studies of ultracold atoms could hold the answer.

7. Shining a light on obscure Nobel prizes

The list of early Nobel laureates in physics is full of famous names – Roentgen, Curie, Becquerel, Rayleigh and so on. But if you go down the list a little further, you’ll find that the 1908 prize went to a now mostly forgotten physicist by the name of Gabriel Lippmann, for a version of colour photography that almost nobody uses (though it’s rather beautiful, as the photo shows). This article tells the story of how and why this happened. A companion piece on the similarly obscure 1912 laureate, Gustaf Dalén, fell just outside this year’s top 10; if you’re a member of the Institute of Physics, you can read both of them together in the November issue of Physics World.

6. How to teach quantum physics to everyone

Why should physicists have all the fun of learning about the quantum world? This episode of the Physics World Weekly podcast focuses on the outreach work of Aleks Kissinger and Bob Coecke, who developed a picture-driven way of teaching quantum physics to a group of 15-17-year-old students. One of the students in the original pilot programme, Arjan Dhawan, is now studying mathematics at the University of Durham, and he joined his former mentors on the podcast to answer the crucial question: did it work?

5. A great physicist’s Nobel-prize-winning mistake

Niels Bohr had many good ideas in his long and distinguished career. But he also had a few that didn’t turn out so well, and this article by science writer Phil Ball focuses on one of them. Known as the Bohr-Kramers-Slater (BKS) theory, it was developed in 1923 with help from two of the assistants/students/acolytes who flocked to Bohr’s institute in Copenhagen. Several notable physicists hated it because it violated both causality and the conservation of energy, and within two years, experiments by Walther Boethe and Hans Geiger proved them right. The twist, though, is that Boethe went on to win a share of the 1954 Nobel Prize for Physics for this work – making Bohr surely one of the only scientists who won himself a Nobel Prize for his good ideas, and someone else a Nobel Prize for a bad one.

4. Reconciling the ideas of Einstein and Newton

Black holes are fascinating objects in their own right. Who doesn’t love the idea of matter-swallowing cosmic maws floating through the universe? For some theoretical physicists, though, they’re also a way of exploring – and even extending – Einstein’s general theory of relativity. This article describes how thinking about black hole collisions inspired Jiaxi Wu, Siddharth Boyeneni and Elias Most to develop a new formulation of general relativity that mirrors the equations that describe electromagnetic interactions. According to this formulation, general relativity behaves the same way as the gravitational described by Isaac Newton more than 300 years ago, with the “gravito-electric” field fading with the inverse square of distance.

3. A list of the century’s best Nobel Prizes for Physics – so far

“Best of” lists are a real win-win. If you agree with the author’s selections, you go away feeling confirmed in your mutual wisdom. If you disagree, you get to have a good old moan about how foolish the author was for forgetting your favourites or including something you deem unworthy. Either way, it’s a success – as this very popular list of the top 5 Nobel Prizes for Physics awarded since the year 2000 (as chosen by Physics World editor-in-chief Matin Durrani) demonstrates.

2. Building bridges between gravity and quantum information theory

We’re back to black holes again for the year’s second-most-read story, which focuses on a possible link between gravity and quantum information theory via the concept of entropy. Such a link could help explain the so-called black hole information paradox – the still-unresolved question of whether information that falls into a black hole is retained in some form or lost as the black hole evaporates via Hawking radiation. Fleshing out this connection could also shed light on quantum information theory itself, and the theorist who’s proposing it, Ginestra Bianconi, says that experimental measurements of the cosmological constant could one day verify or disprove it.

1. The simplest double-slit experiment

Back in 2002, readers of Physics World voted Thomas Young’s electron double-slit experiment “the most beautiful experiment in physics”. More than 20 years later, it continues to fascinate the physics community, as this, the most widely read article of any that Physics World published in 2025, shows.

Young’s original experiment demonstrated the wave-like nature of electrons by sending them through a pair of slits and showing that they create an interference pattern on a screen even when they pass through the slits one-by-one. In this modern update, physicists at the Massachusetts Institute of Technology (MIT), US, stripped this back to the barest possible bones.

Using two single atoms as the slits, they inferred the path of photons by measuring subtle changes in the atoms’ properties after photon scattering. Their results matched the predictions of quantum theory: interference fringes when they didn’t observe the photons’ path, and two bright spots when they did.

It’s an elegant result, and the fact that the MIT team performed the experiment specifically to celebrate the International Year of Quantum Science and Technology 2025 makes its popularity with Physics World readers especially gratifying.

So here’s to another year full of elegant experiments and the theories that inspire them. Long may they both continue, and thank you, as always, for taking the time to read about them.

The post Winning the popularity contest: the 10 most-read physics stories of 2025 appeared first on Physics World.

Our blue planet is a Goldilocks world. We’re at just the right distance from the Sun that Earth – like Baby Bear’s porridge – is not too hot or too cold, allowing our planet to be bathed in oceans of liquid water. But further out in our solar system are icy moons that eschew the Goldilocks principle, maintaining oceans and possibly even life far from the Sun.

We call them icy moons because their surface, and part of their interior, is made of solid water-ice. There are over 400 icy moons in the solar system – most are teeny moonlets just a few kilometres across, but a handful are quite sizeable, from hundreds to thousands of kilometres in diameter. Of the big ones, the best known are Jupiter’s moons, Europa, Ganymede and Callisto, and Saturn’s Titan and Enceladus.

Yet these moons are more than just ice. Deep beneath their frozen shells – some –160 to –200 °C cold and bathed in radiation – lie oceans of water, kept liquid thanks to tidal heating as their interiors flex in the strong gravitational grip of their parent planets. With water being a prerequisite for life as we know it, these frigid systems are our best chance for finding life beyond Earth.

The first hints that these icy moons could harbour oceans of liquid water came when NASA’s Voyager 1 and 2 missions flew past Jupiter in 1979. On Europa they saw a broken and geologically youthful-looking surface, just millions of years old, featuring dark cracks that seemed to have slushy material welling up from below. Those hints turned into certainty when NASA’s Galileo mission visited Jupiter between 1995 and 2003. Gravity and magnetometer experiments proved that not only does Europa contain a liquid layer, but so do Ganymede and Callisto.

Meanwhile at Saturn, NASA’s Cassini spacecraft (which arrived in 2004) encountered disturbances in the ringed planet’s magnetic field. They turned out to be caused by plumes of water vapour erupting out of giant fractures splitting the surface of Enceladus, and it is believed that this vapour originates from an ocean beneath the moon’s ice shell. Evidence for an ocean on Titan is a little less certain, but gravity and radio measurements performed by Cassini and its European-built lander Huygens point towards the possibility of some liquid or slushy water beneath the surface.

Water, ice and JUICE

“All of these ocean worlds are going to be different, and we have to go to all of them to understand the whole spectrum of icy moons,” says Amanda Hendrix, director of the Planetary Science Institute in Arizona, US. “Understanding what their oceans are like can tell us about habitability in the solar system and where life can take hold and evolve.”

To that end, an armada of spacecraft will soon be on their way to the icy moons of the outer planets, building on the successes of their predecessors Voyager, Galileo and Cassini–Huygens. Leading the charge is NASA’s Europa Clipper, which is already heading to Jupiter. Clipper will reach its destination in 2030, with the Jupiter Icy moons Explorer (JUICE) from the European Space Agency (ESA) just a year behind it. Europa is the primary target of scientists because it is possibly Jupiter’s most interesting moon as a result of its “astrobiological potential”. That’s the view of Olivier Witasse, who is JUICE project scientist at ESA, and it’s why Europa Clipper will perform nearly 50 fly-bys of the icy moon, some as low as 25 km above the surface. JUICE will also visit Europa twice on its tour of the Jovian system.

The challenge at Europa is that it’s close enough to Jupiter to be deep inside the giant planet’s magnetosphere, which is loaded with high-energy charged particles that bathe the moon’s surface in radiation. That’s why Clipper and JUICE are limited to fly-bys; the radiation dose in orbit around Europa would be too great to linger. Clipper’s looping orbit will take it back out to safety each time. Meanwhile, JUICE will focus more on Callisto and Ganymede – which are both farther out from Jupiter than Europa is – and will eventually go into orbit around Ganymede.

“Ganymede is a super-interesting moon,” says Witasse. For one thing, at 5262 km across it is larger than Mercury, a planet. It also has its own intrinsic magnetic field – one of only three solid bodies in the solar system to do so (the others being Mercury and Earth).

Beneath the icy exterior

It’s the interiors of these moons that are of the most interest to JUICE and Clipper. That’s where the oceans are, hidden beneath many kilometres of ice. While the missions won’t be landing on the Jovian moons, these internal structures aren’t as inaccessible as we might at first think. In fact, there are three independent methods for probing them.

If a moon’s ocean contains salts or other electrically conductive contaminants, interesting things happen when passing through the parent planet’s variable magnetic field. “The liquid is a conductive layer within a varying magnetic field and that induces a magnetic field in the ocean that we can measure with a magnetometer using Faraday’s law,” says Witasse. The amount of salty contaminants, plus the depth of the ocean, influence the magnetometer readings.

Then there’s radio science – the way that an icy moon’s mass bends a radio signal from a spacecraft to Earth. By making multiple fly-bys with different trajectories during different points in a moon’s orbit around its planet, the moon’s gravity field can be measured. Once that is known to exacting detail, it can be applied to models of that moon’s internal structure.

Perhaps the most remarkable method, however, is using a laser altimeter to search for a tidal bulge in the surface of a moon. This is exactly what JUICE will be doing when in orbit around Ganymede. Its laser altimeter will map the shape of the surface – such as hills and crevasses – but gravitational tidal forces from Jupiter are expected to cause a bulge on the surface, deforming it by 1–10 m. How large the bulge is depends upon how deep the ocean is.

“If the surface ice is sitting above a liquid layer then the tide will be much bigger because if you sit on liquid, you are not attached to the rest of the moon,” says Witasse. “Whereas if Ganymede were solid the tide would be quite small because it is difficult to move one big, solid body.”

As for what’s below the oceans, those same gravity and radio-science experiments during previous missions have given us a general idea about the inner structures of Jupiter’s Europa, Ganymede and Callisto. All three have a rocky core. Inside Europa, the ocean surrounds the core, with a ceiling of ice above it. The rock–ocean interface potentially provides a source of chemical energy and nutrients for the ocean and any life there.

Ganymede’s interior structure is more complex. Separating the 3400 km-wide rocky core and the ocean is a layer, or perhaps several layers, of high-pressure ice, and there is another ice layer above the ocean. Without that rock–ocean interface, Ganymede is less interesting from an astrobiological perspective.

Meanwhile, Callisto, being the farthest from Jupiter, receives the least tidal heating of the three. This is reflected in Callisto’s lack of evolution, with its interior having not differentiated into layers as distinct as Europa and Ganymede. “Callisto looks very old,” says Witasse. “We’re seeing it more or less as it was at the beginning of the solar system.”

Crazy cryovolcanism

Tidal forces don’t just keep the interiors of the icy moons warm. They can also drive dramatic activity, such as cryovolcanoes – icy eruptions that spew out gases and volatile materials like liquid water (which quickly freezes in space), ammonia and hydrocarbons. The most obvious example of this is found on Saturn’s Enceladus, where giant water plumes squirt out through “tiger stripe” cracks at the moon’s south pole.

But there’s also growing evidence of cryovolcanism on Europa. In 2012 the Hubble Space Telescope caught sight of what looked like a water plume jetting out 200 km from the moon. But the discovery is controversial despite more data from Hubble and even supporting evidence found in archive data from the Galileo mission. What’s missing is cast-iron proof for Europa’s plumes. That’s where Clipper comes in.

“We need to find out if the plumes are real,” says Hendrix. “What we do know is if there is plume activity happening on Europa then it’s not as consistent or ongoing as is clearly happening at Enceladus.”

At Enceladus, the plumes are driven by tidal forces from Saturn, which squeeze and flex the 500 km-wide moon’s innards, forcing out water from an underground ocean through the tiger stripes. If there are plumes at Europa then they would be produced the same way, and would provide access to material from an ocean that’s dozens of kilometres below the icy crust. “I think we have a lot of evidence that something is happening at Europa,” says Hendrix.

These plumes could therefore be the key to characterizing the hidden oceans. One instrument on Clipper that will play an important role in investigating the plumes at Europa is an ultraviolet spectrometer, a technique that was very useful on the Cassini mission.

Because Enceladus’ plumes were not known until Cassini discovered them, the spacecraft’s instruments had not been designed to study them. However, scientists were able to use the mission’s ultraviolet imaging spectrometer to analyse the vapour when it was between Cassini and the Sun. The resulting absorption lines in the spectrum showed the plumes to be mostly pure water, ejected into space at a rate of 200 kg per second.

The erupted vapour freezes as it reaches space and some of it snows back down onto the surface. Cassini’s ultraviolet spectrometer was again used, this time to detect solar ultraviolet light reflected and scattered off these icy particles in the uppermost layers of Enceladus’ surface. Scientists found that any freshly deposited snow from the plumes has a different chemistry from older surface material that has been weathered and chemically altered by micrometeoroids and radiation, and therefore a different ultraviolet spectrum.

Icy moon landing

Another two instruments that Cassini’s scientists adapted to study the plumes were the cosmic dust analyser, and the ion and neutral mass spectrometer. When Cassini flew through the fresh plumes and Saturn’s E-ring, which is formed from older plume ejections, it could “taste” the material by sampling it directly. Recent findings from this data indicate that the plumes are rich in salt as well as organic molecules, including aliphatic and cyclic esters and ethers (carbon-bonded acid-based compounds such as fatty acids) (Nature Astron. 9 1662). Scientists also found nitrogen- and oxygen-bearing compounds that play a role in basic biochemistry and which could therefore potentially be building blocks of prebiotic molecules or even life in Enceladus’ ocean.

While Cassini could only observe Enceladus’ plumes and fresh snow from orbit, astronomers are planning a lander that could let them directly inspect the surface snow. Currently in the technology development phase, it would be launched by ESA sometime in the 2040s to arrive at the moon in 2054, when winter at Enceladus’ southern, tiger stripe-adorned pole turns to spring and daylight returns.

“What makes the mission so exciting to me is that although it looks like every large icy moon has an ocean, Enceladus is one where there is a very high chance of actually sampling ocean water,” says Jörn Helbert, head of the solar system section at ESA, and the science lead on the prospective mission.

The planned spacecraft will fly through the plumes with more sophisticated instruments than Cassini’s, designed specifically to sample the vapour (like Clipper will do at Europa). Yet adding a lander could get us even closer to the plume material. By landing close to the edge of a tiger stripe, a lander would dramatically increase the mission’s ability to analyse the material from the ocean in the form of fresh snow. In particular, it would look for biosignatures – evidence of the ocean being habitable, or perhaps even inhabited by microbes.

However, new research urges caution in drawing hasty conclusions about organic molecules present in the plumes and snow. While not as powerful as Jupiter’s, Saturn also has a magnetosphere filled with high-energy ions that bombard Enceladus. A recent laboratory study, led by Grace Richards of the Istituto Nazionale di Astrofisica e Planetologia Spaziale (IAPS-INAF) in Rome, found that when these ions hit surface-ice they trigger chemical reactions that produce organic molecules, including some that are precursors to amino acids, similar to what Cassini tasted in the plumes.

So how can we be sure that the organics in Enceladus’ plumes originate from the ocean, and not from radiation-driven chemistry on the surface? It is the same quandary for dark patches around cracks on the surface of Europa, which seem to be rich with organic molecules that could either originate via upwelling from the ocean below, or just from radiation triggering organic chemistry. A lander on Enceladus might solve not just the mystery of that particular moon, but provide important pointers to explain what we’re seeing on Europa too.

More icy companions

Enceladus is not Saturn’s only icy moon; there’s Titan too. As the ringed planet’s largest moon at 5150 km across, Titan (like Ganymede) is larger than Mercury. However, unlike the other moons in the solar system, Titan has a thick atmosphere rich in nitrogen and methane. The atmosphere is opaque, hiding the surface from spacecraft in orbit except at infrared wavelengths and radar, which means that getting below the smoggy atmosphere is a must.

ESA did this in 2005 with the Huygens lander, which, as it parachuted down to Titan’s frozen surface, revealed it to be a land of hills and dune plains with river channels, lakes and seas of flowing liquid hydrocarbons. These organic molecules originate from the methane in its atmosphere reacting with solar ultraviolet.

Until recently, it was thought that Titan has a core of rock, surrounded by a shell of high-pressure ice, above which sits a layer of salty liquid water and then an outer crust of water ice. However, new evidence from re-analysing Cassini’s data suggests that rather than oceans of liquid water, Titan has “slush” below the frozen exterior, with pockets of liquid water (Nature 648 556). The team, led by Flavio Petricca from NASA’s Jet Propulsion Laboratory, looked at how Titan’s shape morphs as it orbits Saturn. There is a several-hour lag between the moon passing the peak of Saturn’s gravitational pull and its shape shifting, implying that while there must be some form of non-solid substance below Titan’s surface to allow for deformation, more energy is lost or dissipated than would be if it was liquid water. Instead, the researchers found that a layer of high-pressure ice close to its melting point – or slush – better fits the data.

To find out more about Titan, NASA is planning to follow in Huygens’ footsteps with the Dragonfly mission but in an excitingly different way. Set to launch in 2028, Dragonfly should arrive at Titan in 2034 where it will deploy a rotorcraft that will fly over the moon’s surface, beneath the smog, occasionally touching down to take readings. Scientists are intending to use Dragonfly to sample surface material with a mass spectrometer to identify organic compounds and therefore better assess Titan’s biological potential. It will also perform atmospheric and geological measurements, even listening for seismic tremors while landed, which could provide further clues about Titan’s interior.

Jupiter and Saturn are also not the only planets to possess icy moons. We find them around Uranus and Neptune too. Even the dwarf planet Pluto and its largest moon Charon have strong similarities to icy moons. Whether any of these bodies, so far out from the Sun, can maintain an ocean is unclear, however.

Recent findings point to an ocean deep inside Uranus’ moon Ariel that may once have been 170 km deep, kept warm by tidal heating (Icarus 444 116822). But over time Ariel’s orbit around Uranus has become increasingly circular, weakening the tidal forces acting on it, and the ocean has partly frozen. Another of Uranus’ moons, Miranda, has a chaotic surface that appears to have melted and refrozen, and the pattern of cracks on its surface strongly suggests that the moon also contains an ocean, or at least did 150 million years ago. A new mission to Uranus is a top priority in the US’s most recent Decadal Review.

It’s becoming clear that icy ocean moons could far outnumber more traditional habitable planets like Earth, not just in our solar system, but across the galaxy (although none have been confirmed yet). Understanding the internal structures of the icy moons in our solar system, and characterizing their oceans, is vital if we are to expand the search for life beyond Earth.

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Particle and nuclear physics evokes evokes images of huge accelerators probing the extremes of matter. But in this round-up of my favourite research of 2025 I have chosen five stories in which particle and nuclear physics forms the basis for a range of quirky and fascinating research from astrophysics to archaeology.

CERN experiment sheds light on missing blazar radiation

My first pick involves simulating the vast cosmic plasma in the lab. Blazars are extremely bright galaxies that are powered by supermassive black holes. They emit intense jets of radiation, including teraelectronvolt gamma rays – which can be detected by astronomers if a jet happens to point at Earth. As these high-energy photons travel through intergalactic space, they interact with background starlight, producing numerous electron–positron pairs. These pairs should, in theory, generate gigaelectronvolt gamma rays – but this secondary radiation has never been observed. One explanation is that intergalactic magnetic fields deflect these pairs and the resulting gamma rays away from our line of sight. However, there is no conclusive evidence for such fields. Another theory is that plasma instabilities in the sparse intergalactic medium could dissipate the energy of the pair beams. Now, physicists working on the Fireball experiment at CERN have simulated the effect of plasma instabilities by firing a beam of electron–positron pairs through a metre-long argon plasma. They found that plasma instabilities are too weak to account for the missing gamma radiation – strengthening the case for the existence of primordial intergalactic magnetic fields.

Portable source could produce high-energy muon beams

A compact source of muons could soon be discovering hidden chambers in ancient pyramids. Muons are subatomic particles similar to electrons but 200 times heavier. They are produced in copious amounts in the atmosphere by cosmic rays. These cosmic muons can penetrate long distances into materials and are finding increasing use in “muon tomography” – a technique that has imaged the interiors of huge objects such as volcanoes, pyramids and nuclear reactors. One downside of muon tomography is that muons are always vertically incident, limiting opportunities for imaging. While beams of muons can be made in accelerators, these are large and expensive facilities – and the direction of such beams are also fixed. Now, physicists at Lawrence Berkeley National Laboratory have demonstrated a compact, and potentially portable method for generating high-energy muon beams using laser plasma acceleration. It uses an ultra-intense, tightly focused laser pulse to accelerate electrons in a short plasma channel. These electrons then strike a metal target creating a muon beam. With more work, compact and portable muon sources could be developed, leading to new possibilities for non-destructive imaging in archaeology, geology, and nuclear safety.

Radioactive BEC could be a ‘superradiant neutrino laser’

Could a “superradiant neutrino laser” be created using radioactive atoms in an ultracold Bose–Einstein condensate (BEC)? The answer is “maybe”, according to theoretical work by two physicists in the US. Their proposal involves creating a BEC of rubidium-83, which undergoes beta decay involving the emission of neutrinos. Unlike photons, neutrinos are fermions and therefore cannot form the basis of conventional laser. However, if the atoms in the BEC are close enough together, quantum interactions between the atomic nuclei could accelerate beta decay and create a coherent, laser-like burst of neutrinos. This is a well-known phenomenon called superradiance. While the idea could be tested using existing technologies for making BECs, it would be a challenge to deploy radioactive rubidium in a conventional atomic physics lab. Another drawback is that there are no obvious applications for a neutrino laser – at least for now. However, the very idea of a neutrino laser is so cool that I am hoping that someone will try to build one soon!

Antimatter could be transported by road

If you happen to be driving between Geneva and Dusseldorf in the future, you might just overtake a shipment of antimatter. It will be on its way to an experiment that could solve some of the biggest mysteries in physics – including why there is much more matter than antimatter in the universe. While antielectrons (positrons) can be created in a small lab, antiprotons can only be created at large and expensive accelerators. This limits where antimatter experiments can be done. But now, physicists on the BASE collaboration at CERN have shown that it should be possible to transport antiprotons by road. Protons stood in for antiprotons in their demonstration and the particles were held in an electromagnetic trap at cryogenic temperatures and ultralow pressure. By transporting their BASE-STEP system around CERN’s Meyrin site, they showed it was stable and robust enough to handle the rigors of road travel.  The system will now be re-configured to transport antiprotons about 700 km to Germany’s Heinrich Heine University. There, physicists hope to search for charge–parity–time (CPT) violations in protons and antiprotons with a precision at least 100 times higher than is currently possible at CERN. The BASE collaboration is also cited in our Top 10 Breakthroughs of 2025 for their quantum control of a single antiproton.

Solid-state nuclear clock ticks ever closer

Solid quartz crystals revolutionized time keeping in the 20th century, so could solid-state nuclear clocks soon do the same? Today, the best timekeepers use the light emitted in atomic transitions. In principle, even better clocks could be made using very-low-energy gamma-rays emitted in some nuclear transitions. Nuclei are much smaller than atoms and these transitions are governed by the strong force. This means that such nuclear clocks would be far less susceptible to performance-degrading electromagnetic noise. And unlike atomic clocks, the nuclei could be embedded in solids – which would greatly simplify clock design. Thorium-229 shows great promise as a clock nucleus but it has two practical shortcomings: it is radioactive and extremely expensive. The solution to both of these problems is a clock design that uses only a tiny amount of thorium-229. Now researchers in the US have shown that physical vapour deposition can used to create extremely thin films of thorium tetrafluoride. Characterization using a vacuum ultraviolet laser confirmed the accessibility of the clock transition – but its lifetime was shorter and the signal less intense than measured in thorium-doped crystals. However, the researchers believe that these unexpected results should not dissuade those aiming to build nuclear clocks.

 

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There’s only a few days left in the International Year of Quantum Science and Technology, but we’re still finding plenty to celebrate here at Physics World HQ thanks to a long list of groundbreaking work by quantum physicists in 2025. Here are a few of our favourite stories from the past 12 months.

Observing negative time in atom-photon interactions

By this point in 2025, “negative time” may sound like the answer to the question “How long have I got left to buy holiday presents for my loved ones?” Earlier in the year, though, physicists led by experimentalist Aephraim Steinberg of the University of Toronto, Canada and theorist Howard Wiseman of Griffith University in Australia showed that the concept can also describe the average amount of time a photon spends in an excited atomic state. While experts have cautioned against interpreting “negative time” too literally – we aren’t in time machine territory here – it does seem like there’s something interesting going on in this system of ultracold rubidium atoms.

Creating an operating system for quantum networks

It is a truth universally acknowledged that any sufficiently advanced technology must be in want of a simple system to operate it. In April, the quantum world passed this milestone thanks to Stephanie Wehner and colleagues at Delft University of Technology in the Netherlands. Their operating system is called QNodeOS, and they developed it with the aim of improving access to quantum computing for the 99.99999% percent of people who aren’t (and mostly don’t need to be) intimately familiar with how quantum information processors work. Another advantage of QNodeOS is that it makes it easier for classical and quantum machines (and quantum devices built with different qbit architectures) to communicate with each other.

Pushing the boundary between the quantum and classical worlds

How big does an object have to be before it stops being quantum and starts behaving like the billiard-ball-like solids familiar from introductory classical mechanics courses? It’s a question that featured in our annual “Breakthrough of the Year” back in 2021, when two independent teams demonstrated quantum entanglement in pairs of 10-micron drumheads, and we’re returning to it this year in a different system: levitated nanoparticles around 100 nm in diameter.

In one boundary-pushing experiment, Massimiliano Rossi and colleagues at ETH Zurich, Switzerland and the Institute of Photonic Sciences in Barcelona, Spain cooled silica nanoparticles enough to extend their wave-like behaviour to 73 pm. In another study, Kiyotaka Aikawa and colleagues at the University of Tokyo, Japan performed the first quantum mechanical squeezing on a nanoparticle, narrowing its velocity distribution at the expense of its momentum distribution. We may not know exactly where the quantum-classical boundary is yet, but the list of quantum behaviours we’ve observed in usually-not-quantum objects keeps getting longer.

Using a quantum computer to generate quantum random numbers

What’s the best way to generate random numbers? In part, the answer depends on how random those numbers really need to be. For many applications, the pseudorandom numbers generated by classical computers, or the random-but-with-systematic-biases numbers found in, say, radio static, are good enough. But if you really, really need those numbers to be random, you need a quantum source – and thanks to work published this year by Scott Aaronson, Shi-Han Hung, Marco Pistoia and colleagues, that quantum source can now be a quantum computer. Which is a neat way of tying things together, don’t you think?

Giving Schrödinger’s cats a nuclear option

Finally, we would be remiss not to mention the work of Andrea Morello and colleagues at the University of New South Wales, Australia. This year, they became the first to create quantum superpositions known as a Schrödinger’s cat states in a heavy atom, antimony, that has a large nuclear spin. They also created what is certainly the year’s best scientific team photo, posing with cats on their laps and deadpan expressions more usually associated with too-cool-for-school indie musicians.

So congratulations to them, and to all the other teams in this list, for setting the bar high in a year that offered plenty for the quantum community to celebrate. We hope you enjoyed the International Year of Quantum Science and Technology, and we look forward to many more exciting discoveries in 2026.

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This year saw Physics World report on a raft of innovative and exciting developments in the worlds of medical physics and biotech. These included novel cancer therapies using low-temperature plasma or laser ablation, intriguing new devices such as biodegradable bone screws and a pacemaker smaller than a grain of rice, and neural engineering breakthroughs including an ultrathin bioelectric implant that improves movement in rats with spinal cord injuries and a tiny brain sensor that enables thought control of external devices. Here are a few more research highlights that caught my eye.

Vision transformed

One remarkable device introduced in 2025 was an eye implant that restored vision to patients with incurable sight loss. In a clinical study headed up at the University of Bonn, participants with sight loss due to age-related macular degeneration had a tiny wireless implant inserted under their retina. Used in combination with specialized glasses, the system restored the ability to read in 27 of 32 participants followed up a year later.

We also described a contact lens that enables wearers to see near-infrared light without night vision goggles, reported on an fascinating retinal stimulation technique that enabled volunteers to see colours never before seen by the human eye, and chatted with researchers in Hungary about how a tiny dissolvable eye insert they are developing could help astronauts suffering from eye conditions.

Radiation therapy advances

2025 saw several firsts in the field of radiation therapy. Researchers in Germany performed the first cancer treatment using a radioactive carbon ion beam, on a mouse with a bone tumour close to the spine. And a team at the Trento Proton Therapy Centre in Italy delivered the first clinical treatments using proton arc therapy – a development that made it onto our top 10 Breakthroughs of the Year.

Meanwhile, the ASTRO meeting saw Leo Cancer Care introduce its first upright photon therapy system, called Grace, which will deliver X-ray radiation to patients in an upright position. This new take on radiation delivery is also under investigation by a team at RaySearch Laboratories, who showed that combining static arcs and shoot-through beams could increase plan quality and reduce delivery times in upright proton therapy.

Among other new developments, there’s a low-cost, dual-robot radiotherapy system built by a team in Canada and targeted for use in low-resource settings, a study from Australia showing that combining microbeam radiation therapy with targeted radiosensitizers can optimize brain cancer treatment, and an investigation at Moffitt Cancer Center examining how skin luminance imaging improves Cherenkov-based radiotherapy dosimetry.

The impact of AI

It’s particularly interesting to examine how the rapid evolution of artificial intelligence (AI) is impacting healthcare, especially considering its potential for use in data-intensive tasks. Earlier this year, a team at Northwestern Medicine integrated a generative AI tool into a live clinical workflow for the first time, using it to draft radiology reports on X-ray images. In routine use, the AI model increased documentation efficiency by an average of 15.5%, while maintaining diagnostic accuracy.

Other promising applications include identifying hidden heart disease from electrocardiogram traces, contouring targets for brachytherapy treatment planning and detecting abnormalities in blood smear samples.

When introducing AI into the clinic, however, it’s essential that any AI-driven software is accurate, safe and trustworthy. To help assess these factors, a multinational research team identified potential pitfalls in the evaluation of algorithmic bias in AI radiology models, suggesting best practices to mitigate such bias.

A quantum focus

Finally, with 2025 being the International Year of Quantum Science and Technology, Physics World examined how quantum physics looks set to play a key role in medicine and healthcare. Many quantum-based companies and institutions are already working in the healthcare sector, with quantum sensors, in particular, close to being commercialized. As detailed in this feature on quantum sensing, such technologies are being applied for applications ranging from lab and point-of-care diagnostics to consumer wearables for medical monitoring, body scanning and microscopy.

Alongside, scientists at Jagiellonian University are applying quantum entanglement to cancer diagnostics and developing the world’s first whole-body quantum PET scanner, while researchers at the University of Warwick have created an ultrasensitive magnetometer based on nitrogen-vacancy centres in diamond that could detect small cancer metastases via keyhole surgery. There’s even a team designing a protein qubit that can be produced directly inside living cells and used as a magnetic field sensor (which also featured in this year’s top 10 breakthroughs).

And in September, we ran a Physics World Live event examining how quantum optics, quantum sensors and quantum entanglement can enable advanced disease diagnostics and transform medical imaging. The recording is available to watch here.

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How well have you been following events in physics? There are 20 questions in total: blue is your current question and white means unanswered, with green and red being right and wrong.

16–20 Top quark – congratulations, you’ve hit Einstein level

11–15 Strong force – good but not quite Nobel standard

6–10 Weak force – better interaction needed

0–5 Bottom quark – not even wrong

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ZAP-X is a next-generation, cobalt-free, vault-free stereotactic radiosurgery system purpose-built for the brain. Delivering highly precise, non-invasive treatments with exceptionally low whole-brain and whole-body dose, ZAP-X’s gyroscopic beam delivery, refined beam geometry and fully integrated workflow enable state-of-the-art SRS without the burdens of radioactive sources or traditional radiation bunkers.

Theresa Hofman is deputy head of medical physics at the European Radiosurgery Center Munich (ERCM), specializing in stereotactic radiosurgery with the CyberKnife and ZAP‑X systems. She has been part of the ERCM team since 2018 and has extensive clinical experience with ZAP‑X, one of the first centres worldwide to implement the technology in 2021. Since then, the team has treated more than 900 patients with ZAP‑X, and she is deeply involved in both clinical use and evaluation of its planning software.

She holds a master’s degree in physics from Ludwig Maximilian University of Munich, where she authored two first‑author publications on range verification in carbon‑ion therapy. At ERCM, she has published additional first‑author studies on CyberKnife kidney‑treatment accuracy and on comparative planning between ZAP‑X and CyberKnife. She is currently conducting further research on the latest ZAP‑X planning software. Her work is driven by the goal of advancing high‑quality radiosurgery and ensuring the best possible treatment for every patient.

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This episode of the Physics World Weekly podcast features Pat Hanrahan, who studied nuclear engineering and biophysics before becoming a founding employee of Pixar Animation Studios. As well as winning three Academy Awards for his work on computer animation, Hanrahan won the Association for Computing Machinery’s A.M. Turing Award for his contributions to 3D computer graphics, or CGI.

Earlier this year, Hanrahan spoke to Physics World’s Margaret Harris at the Heidelberg Laureate Forum in Germany. He explains how he was introduced to computer graphics by his need to visualize the results of computer simulations of nervous systems. That initial interest led him to Pixar and his development of physically-based rendering, which uses the principles of physics to create realistic images.

Hanrahan explains that light interacts with different materials in very different ways, making detailed animations very challenging. Indeed, he says that creating realistic looking skin is particularly difficult – comparing it to the quest for a grand unified theory in physics.

He also talks about how having a background in physics has helped his career – citing his physicist’s knack for creating good models and then using them to solve problems.

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Electrochemical impedance spectroscopy (EIS) provides valuable insights into the physical processes within batteries – but how can these measurements directly inform physics-based models? In this webinar, we present recent work showing how impedance data can be used to extract grouped parameters for physics-based models such as the Doyle–Fuller–Newman (DFN) model or the reduced-order single-particle model with electrolyte (SPMe).

We will introduce PyBaMM (Python Battery Mathematical Modelling), an open-source framework for flexible and efficient battery simulation, and show how our extension, PyBaMM-EIS, enables fast numerical impedance computation for any implemented model at any operating point. We also demonstrate how PyBOP, another open-source tool, performs automated parameter fitting of models using measured impedance data across multiple states of charge.

Battery modelling is challenging, and obtaining accurate fits can be difficult. Our technique offers a flexible way to update model equations and parameterize models using impedance data.

Join us to see how our tools create a smooth path from measurement to model to simulation.

An interactive Q&A session follows the presentation.

Noël Hallemans is a postdoctoral research assistant in engineering science at the University of Oxford, where he previously lectured in mathematics at St Hugh’s College. He earned his PhD in 2023 from the Vrije Universiteit Brussel and the University of Warwick, focusing on frequency-domain, data-driven modelling of electrochemical systems.

His research at the Battery Intelligence Lab, led by Professor David Howey, integrates electrochemical impedance spectroscopy (EIS) with physics-based modelling to improve understanding and prediction of battery behaviour. He also develops multisine EIS techniques for battery characterisation during operation (for example, charging or relaxation).

 

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A new measurement by CERN’s ATLAS Collaboration has strengthened evidence that the masses of fundamental particles originate through their interaction with the Higgs field. Building on earlier results from CERN’s CMS Collaboration, the observations suggest that muon–antimuon pairs (dimuons) can be created by the decay of Higgs bosons.

In the Standard Model of particle physics, the fermionic particles are organized into three different generations, broadly in terms of their masses. The first generation comprises the two lightest quarks (up and down), the lightest lepton (the electron) and the electron neutrino. The second includes the strange and charm quarks, the muon and its neutrino; and the third generation the bottom and top quarks, the tau and its neutrino. In terms of the charged fermions, the top quark is nearly 340,000 times heavier than the lightest – the electron.

All of the quarks and leptons have both right- and left-handed components, which relate to the direction of a particle’s spin relative to its direction of motion (right-handed if both directions are aligned; left-handed if they are anti-aligned).

Right- and left-handed particles are treated the same by the strong and electromagnetic forces, regardless of their generation in the Standard Model. The weak force, however, only acts on left-handed particles.

Flipping handedness

In the 1960s, Steven Weinberg uncovered a theoretical solution to this seemingly bizarre asymmetry. He proposed that the Higgs field acts as a bridge between each particle’s left- and right-handed components, in a way that respects the Standard Model’s underlying symmetry. This interaction causes the particle to constantly flip between its two components, creating a resistance to motion that can be perceived as mass.

However, this deepens the mystery. According to Weinberg’s theory, higher-mass particles must interact more strongly with this Higgs field – but in contrast, the strong and electromagnetic forces can only differentiate between these particles according to their charges (colour and electrical). The question is how does Higgs field can distinguish between particles in different generations if their charges are identical?

Key to solving this mystery will be to observe the decay products of Higgs bosons with different interaction strengths. For stronger interactions, corresponding to heavier generations, these decays should become far more likely.

In 2022, both the ATLAS and CMS collaborations did just this. Through proton–proton collision experiments at CERN’s Large Hadron Collider (LHC), the groups independently observed Higgs bosons decaying to tau–antitau pairs. This relatively common process occurred at the same rate as predicted by theory.

Rare decay

A year earlier, similar experiments by the CMS collaboration probed the second generation by observing muon–antimuon pairs from the decays of Higgs bosons. This rarer event occurs in just 1 in 5000 Higgs decays.

In their latest study, the ATLAS collaboration have now reproduced this CMS result independently. They collided protons at about 13 TeV and observed muon–antimuon pairs in the same range of energies predicted by theory.

Through the improvements they offer on the earlier CMS analysis, these new results bring dimuon observations to a statistical significance of 3.4σ. This is well below the 5σ standard required for the observation to be considered a discovery, so more work is needed.

The research could also provide guidance in the search for much rarer Higgs interactions that involve first-generation particles. This includes decay electron–positron pairs, originating from Higgs bosons which decay in just 1 in 200 million cases.

The research is described in Physical Review Letters.

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Russia wants to revive a Soviet-era particle accelerator that has been abandoned since the 1990s. The Kurchatov Institute for High Energy Physics has allocated 176 million rubles ($25m) to assess the current condition of the unfinished 600 GeV Proton Accelerator and Storage Complex (UNK) in Protvino near Moscow. The move is part of plans to strengthen Russia’s technological sovereignty and its activity in high-energy physics.

Although work on the UNK was officially halted in the 1990s, construction only ceased in 2013. At that time, a 21 km tunnel had been built at a depth of 60 m along with underground experimental hall lighting and ventilation systems.

In February 2025, physicist Mikhail Kovalchuk, president of the Kurchatov Institute National Research Center, noted in Russia’s Kommersant newspaper that enormous intellectual and material resources had been invested in the UNK’s design and development before it was cancelled.

According to Kovalchuk, Western sanctions provided an additional impetus to restore the project, as scientists that had previously worked in CERN projects could no longer do so.

“By participating in [CERN] projects, we not only preserved our scientific potential and survived a difficult period, but also enriched ourselves intellectually and technologically,” added Kovalchuk. “Today we are self-sufficient.”

Anatoli Romaniouk, a Russian particle physicist who has worked at CERN since 1990, told Physics World that a revival of the UNK will at least maintain fundamental physics research in Russia.

“If this project is realized, then there is hope that it will be possible to at least somewhat slow down the scientific lag of Russian physics with global science,” says Romaniouk.

While official plans for the accelerator have not been disclosed, it is thought that the proton beam energy could be upgraded to reach 3 TeV. Romaniouk says it is also unclear what kind of science will be done with the accelerator, which will depend on what ideas come forward.

Yet some Russian scientists say that it could be used to produce neutrinos. This would involve putting a neutrino detector nearby to characterize the beam before it is sent some 4000 km towards Lake Baikal where a neutrino detector – the Baikal Deep Underwater Neutrino Telescope – is already installed 1 km underground.

“I think it’s possible to find an area of ​​high-energy physics where the research with the help of this collider could be beneficial,” adds Romaniouk.

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Achieving a profound understanding of any subject is hard. When that subject is quantum mechanics, it’s even harder. And when one departs from ideal theoretical scenarios and enters the real world of experimental limitations, it becomes more challenging still – yet that is what physicists at the Freie Universität Berlin (FU-Berlin), Germany recently did by exploring what happens to entanglement theory in real quantum computers. In doing so, they created a bridge between two fields that have so far largely developed in parallel: entanglement theory (rooted in physics) and computational complexity (rooted in computer science).

Ebits, the standard currency of entanglement

In quantum mechanics, a composite system is said to be entangled when its total wavefunction cannot be written as a product of the states of its individual subsystems. This leads to correlations between subsystems that arise from the structure of the quantum state, not from any shared classical information. Many speed-ups achieved in quantum computing, quantum cryptography and quantum metrology rely heavily on entanglement, but not every form of entanglement is equally useful. Only specific kinds of entanglement will enable a given computational or communication task.

To make quantum technologies practical, the available entangled resources must therefore often be converted into forms suitable for specific applications. One major conversion process involves transforming partially entangled states into, or extracting them from, the maximally entangled bit (ebit) that acts as the standard unit of entanglement. High-fidelity ebits – entangled pairs that are extremely close to the ideal perfectly entangled state – can be distilled from noisy or imperfect entangled states through entanglement distillation, while entanglement dilution allows one to reconstruct the desired entangled states from purified ebits.

In an idealized setting, with an infinite number of copies of entangled states and unlimited computational power, a single quantity called the von Neumann entropy fully determines how many ebits can be extracted or are required. But reality is far less forgiving: we never have infinite resources, and computational power is always limited, just like we don’t have an infinite amount of gold on Earth.

Entanglement under finite resources

In the present work, which is published in Nature Physics, the FU-Berlin team of Lorenzo Leone, Jacopo Rizzo, Jens Eisert and Sofiene Jerbi asked what happens when these ideal assumptions break down. They study the case where only a finite number of entangled states, which can scale at most polynomially with the number of quantum bits (qubits) in the system, are considered and all local operations and classical communication (LOCC) are performed in a finite polynomial time.

They found that the simple correspondence between von Neumann entropy and extractable or required ebits no longer holds: even when a state has a large von Neumann entropy, the number of ebits that can be efficiently extracted may be much lower. In these cases, the number is bounded instead by the min-entropy of the reduced state (an operational measure determined solely by the state’s largest eigenvalue that captures how much entanglement can be reliably distilled from a single copy of the state) without averaging over many uses. On the other hand, even a state with negligible von Neumann entanglement may require a maximal ebit budget for efficient dilution.

Leone and Eisert say they were inspired to perform this study by recent work on so-called pseudo-entangled states, which are states that look at lot more entangled than they are for computationally bounded observers. Their construction of pseudo-entangled states highlights a dramatic worst-case scenario: a state that appears almost unentangled by conventional measures may still require a large number of ebits to create it efficiently. The takeaway is that computability matters, and quantum resources you might have thought were available may be, in effect, locked away simply because they cannot be processed efficiently. In other words, practical limitations make the line between a “resource” and a “usable resource” even sharper.

Quantum resources in a limited world

The researchers say that their study raises multiple questions for future exploration. One such question concerns whether a similar computational‐efficiency gap exists for other quantum resources such as magic and coherence. Another is whether one can build a full resource theory with complexity constraints, where quantities reflect not just what can be converted, but how efficient that conversion is.

Regardless of the answers, the era of entanglement under infinite book‐keeping is giving way to an era of entanglement under limited books, limited clocks and limited gates. And in this more realistic space, quantum technologies may still shine, but the calculus of what can be done and what can be harnessed needs a serious retooling.

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Brachytherapy – a cancer treatment that destroys tumours using small radioactive sources implanted inside the body – plays a critical role in treating cervical cancer, offering an important option for patients with inoperable locally advanced disease. Brachytherapy can deliver high radiation doses directly to the tumour while ensuring nearby healthy tissues receive minimal dose; but its effectiveness relies on accurate delineation of the treatment target. A research team in China is using a hybrid deep-learning model to help with this task.

Planning brachytherapy treatments requires accurate contouring of the clinical target volume (CTV) on a CT scan, a task that’s traditionally performed manually. The limited soft-tissue contrast of CT, however, can result in unclear target boundaries, while applicator or needle insertion (used to deliver the radioactive sources) can deform and displace nearby organs. This makes manual contouring a time-consuming and subjective task that requires a high level of operator expertise.

Automating this process could reduce reliance on operator experience, increase workflow efficiency and improve contouring consistency. With this aim, the research team – headed up by He Ma from Northeastern University and Lin Zhang from Shanghai University of International Business and Economics – developed a 3D hybrid neural network called BCTVNet.

Currently, most brachytherapy segmentation models are based on convolutional neural networks (CNNs). CNNs effectively capture local structural features and can model fine anatomical details but struggle with long-range dependencies, which can cause problems if the target extends across multiple CT slices. Another option is to use transformer-based models that can integrate spatial information across distant regions and slices; but these are less effective at capturing fine-grained local detail.

To combine the strengths of both, BCTVNet integrates CNN with transformer branches to provide strong local detail extraction along with global information integration. BCTVNet performs 3D segmentation directly on post-insertion CT images, enabling the CTV to be defined based on the actual treatment geometry.

Model comparisons

Zhang, Ma and colleagues assessed the performance of BCTVNet using a private CT dataset from 95 patients diagnosed with locally advanced cervical cancer and treated with CT-guided 3D brachytherapy (76 in the training set, 19 in the test set). The scans had an average of 96 slices per patient and a slice thickness of 3 mm.

CT scans used to plan cervical cancer brachytherapy often exhibit unclear target boundaries. To enhance the local soft-tissue contrast and improve boundary recognition, the researchers pre-processed the CT volumes with a 3D version of the CLAHE (contrast-limited adaptive histogram equalization) algorithm, which processes the entire CT scan as a volumetric input. They then normalized the intensity values to standardize the input for the segmentation models.

The researchers compared BCTVNet with 12 popular CNN- and transformer-based segmentation models, evaluating segmentation performance via a series of metrics, including Dice similarity coefficient (DSC), Jaccard index, Hausdorff distance 95th percentile (HD95) and average surface distance.

Contours generated by BCTVNet were closest to the ground truth, reaching a DSC of 83.24% and a HD95 (maximum distance from ground truth excluding the worst 5%) of 3.53 mm. BCTVNet consistently outperformed the other models across all evaluation metrics. It also demonstrated strong classification accuracy, with a precision of 82.10% and a recall of 85.84%, implying fewer false detections and successful capture of target regions.

To evaluate the model’s generalizability, the team conducted additional experiments on the public dataset SegTHOR, which contains 60 thoracic 3D CT scans (40 for training, 20 for testing) from patients with oesophageal cancer. Here again, BCTVNet achieved the best scores among all the segmentation models, with the highest average DSC of 87.09% and the lowest average HD95 of 7.39 mm.

“BCTVNet effectively overcomes key challenges in CTV segmentation and achieves superior performance compared to existing methods,” the team concludes. “The proposed approach provides an effective and reliable solution for automatic CTV delineation and can serve as a supportive tool in clinical workflows.”

The researchers report their findings in Machine Learning: Science and Technology.

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The Physics World 2025 Breakthrough of the Year is awarded to Guangyu Zhang, Luojun Du  and colleagues at the Institute of Physics of the Chinese Academy of Sciences for producing the first 2D sheets of metal. The team produced five atomically thin 2D metals – bismuth, tin, lead, indium and gallium – with the thinnest being around 6.3 Å. The researchers say their work is just the “tip of the iceberg” and now aim to use their new materials to probe the fundamentals of physics. Their breakthrough could also lead to the development of new technologies.

Since the discovery of graphene – a sheet of carbon just one atom thick – in 2004, hundreds of other 2D materials have been fabricated and studied. In most of these, layers of covalently bonded atoms are separated by gaps where neighbouring layers are held together only by weak van der Waals (vdW) interactions, making it relatively easy to “shave off” single layers to make 2D sheets. Many thought that making atomically thin metals would be impossible given that each atom in a metal is strongly bonded to surrounding atoms in all directions.

The technique developed by Zhang, Du and colleagues involves heating powders of pure metals between two monolayer-MoS2/sapphire vdW anvils. Once the metal powders are melted into a droplet, the researchers applied a pressure of 200 MPa and continued this “vdW squeezing” until the opposite sides of the anvils cooled to room temperature and 2D sheets of metal were formed.

“Right now, we have reported five single element metals, but actually we can do more because of the 88 metals in the periodic table,” Zhang explains in today’s episode of the Physics World Weekly podcast. In the podcast, he also talks about the team’s motivation creating 2D metals and some of the possible technological applications of the materials.

The Breakthrough of the Year was chosen by the Physics World editorial team. We looked back at all the scientific discoveries we have reported on since 1 January and picked the most important. In addition to being reported in Physics World in 2025, the breakthrough must meet the following criteria:

• Significant advance in knowledge or understanding

• Importance of work for scientific progress and/or development of real-world applications

• Of general interest to Physics World readers

Before we picked our winners, we released the Physics World Top 10 Breakthroughs for 2025, which served as our shortlist. The other nine breakthroughs are listed below in no particular order.

Finding the stuff of life on an asteroid

To Tim McCoy, Sara Russell, Danny Glavin, Jason Dworkin, Yoshihiro Furukawa, Ann Nguyen, Scott Sandford, Zack Gainsforth and an international team of collaborators for identifying salt, ammonia, sugar, nitrogen- and oxygen-rich organic materials, and traces of metal-rich supernova dust, in samples returned from the near-Earth asteroid 101955 Bennu. The incredible chemical richness of this asteroid, which NASA’s OSIRIS-REx spacecraft visited in 2020, lends support to the longstanding hypothesis that asteroid impacts could have “seeded” the early Earth with the raw ingredients needed for life to form. The discoveries also enhance our understanding of how Bennu and other objects in the solar system formed out of the disc of material that coalesced around the young Sun.

The first superfluid molecule

To Takamasa Momose of the University of British Columbia, Canada, and Susumu Kuma of the RIKEN Atomic, Molecular and Optical Physics Laboratory, Japan for observing superfluidity in a molecule for the first time. Molecular hydrogen is the simplest and lightest of all molecules, and theorists predicted that it would enter a superfluid state at a temperature between 1‒2 K. But this is well below the molecule’s freezing point of 13.8 K, so Momose, Kuma and colleagues first had to develop a way to keep the hydrogen in a liquid state. Once they did that, they then had to work out how to detect the onset of superfluidity. It took them nearly 20 years, but by confining clusters of hydrogen molecules inside helium nanodroplets, embedding a methane molecule within the clusters, and monitoring the methane’s rotation, they were finally able to do it. They now plan to study larger clusters of hydrogen, with the aim of exploring the boundary between classical and quantum behaviour in this system.

Hollow-core fibres break 40-year limit on light transmission

To researchers at the University of Southampton and Microsoft Azure Fiber in the UK, for developing a new type of optical fibre that reduces signal loss, boosts bandwidth and promises faster, greener communications. The team, led by Francesco Poletti, achieved this feat by replacing the glass core of a conventional fibre with air and using glass membranes that reflect light at certain frequencies back into the core to trap the light and keep it moving through the fibre’s hollow centre. Their results show that the hollow-core fibres exhibit 35% less attenuation than standard glass fibres – implying that fewer amplifiers would be needed in long cables – and increase transmission speeds by 45%. Microsoft has begun testing the new fibres in real systems, installing segments in its network and sending live traffic through them. These trials open the door to gradual rollout and Poletti suggests that the hollow-core fibres could one day replace existing undersea cables.

First patient treatments delivered with proton arc therapy

To Francesco Fracchiolla and colleagues at the Trento Proton Therapy Centre in Italy for delivering the first clinical treatments using proton arc therapy (PAT). Proton therapy – a precision cancer treatment – is usually performed using pencil-beam scanning to precisely paint the dose onto the tumour. But this approach can be limited by the small number of beam directions deliverable in an acceptable treatment time. PAT overcomes this by moving to an arc trajectory with protons delivered over a large number of beam angles and the potential to optimize the number of energies used for each beam direction. Working with researchers at RaySearch Laboratories in Sweden, the team performed successful dosimetric comparisons with clinical proton therapy plans. Following a feasibility test that confirmed the viability of clinical PAT delivery, the researchers used PAT to treat nine cancer patients. Importantly, all treatments were performed using the centre’s existing proton therapy system and clinical workflow.

A protein qubit for quantum biosensing

To Peter Maurer and David Awschalom at the University of Chicago Pritzker School of Molecular Engineering and colleagues for designing a protein quantum bit (qubit) that can be produced directly inside living cells and used as a magnetic field sensor. While many of today’s quantum sensors are based on nitrogen–vacancy (NV) centres in diamond, they are large and hard to position inside living cells. Instead, the team used fluorescent proteins, which are just 3 nm in diameter and can be produced by cells at a desired location with atomic precision. These proteins possess similar optical and spin properties to those of NV centre-based qubits – namely that they have a metastable triplet state. The researchers used a near-infrared laser pulse to optically address a yellow fluorescent protein and read out its triplet spin state with up to 20% spin contrast. They then genetically modified the protein to be expressed in bacterial cells and measured signals with a contrast of up to 8%. They note that although this performance does not match that of NV quantum sensors, it could enable magnetic resonance measurements directly inside living cells, which NV centres cannot do.

Highest-resolution images ever taken of a single atom

To the team led by Yichao Zhang at the University of Maryland and Pinshane Huang of the University of Illinois at Urbana-Champaign for capturing the highest-resolution images ever taken of individual atoms in a material. The team used an electron-microscopy technique called electron ptychography to achieve a resolution of 15 pm, which is about 10 times smaller than the size of an atom. They studied a stack of two atomically-thin layers of tungsten diselenide, which were rotated relative to each other to create a moiré superlattice. These twisted 2D materials are of great interest to physicists because their electronic properties can change dramatically with small changes in rotation angle. The extraordinary resolution of their microscope allowed them to visualize collective vibrations in the material called moiré phasons. These are similar to phonons, but had never been observed directly until now. The team’s observations align with theoretical predictions for moiré phasons. Their microscopy technique should boost our understanding of the role that moiré phasons and other lattice vibrations play in the physics of solids. This could lead to the engineering of new and useful materials.

Quantum control of individual antiprotons

To CERN’s BASE collaboration for being the first to perform coherent spin spectroscopy on a single antiproton – the antimatter counterpart of the proton. Their breakthrough is the most precise measurement yet of the antiproton’s magnetic properties, and could be used to test the Standard Model of particle physics. The experiment begins with the creation of high-energy antiprotons in an accelerator. These must be cooled (slowed down) to cryogenic temperatures without being lost to annihilation. Then, a single antiproton is held in an ultracold electromagnetic trap, where microwave pulses manipulate its spin state. The resulting resonance peak was 16 times narrower than previous measurements, enabling a significant leap in precision. This level of quantum control opens the door to highly sensitive comparisons of the properties of matter (protons) and antimatter (antiprotons). Unexpected differences could point to new physics beyond the Standard Model and may also reveal why there is much more matter than antimatter in the visible universe.

A smartphone-based early warning system for earthquakes

To Richard Allen, director of the Berkeley Seismological Laboratory at the University of California, Berkeley, and Google’s Marc Stogaitis and colleagues for creating a global network of Android smartphones that acts as an earthquake early warning system. Traditional early warning systems use networks of seismic sensors that rapidly detect earthquakes in areas close to the epicentre and issue warnings across the affected region. Building such seismic networks, however, is expensive, and many earthquake-prone regions do not have them. The researchers utilized the accelerometer in millions of phones in 98 countries to create the Android Earthquake Alert (AEA) system. Testing the app between 2021 and 2024 led to the detection of an average of 312 earthquakes a month, with magnitudes ranging from 1.9 to 7.8. For earthquakes of magnitude 4.5 or higher, the system sent “TakeAction” alerts to users, sending them, on average, 60 times per month for an average of 18 million individual alerts per month. The system also delivered lesser “BeAware” alerts to regions expected to experience a shaking intensity of magnitude 3 or 4. The team now aims to produce maps of ground shaking, which could assist the emergency response services following an earthquake.

A “weather map” for a gas giant exoplanet

To Lisa Nortmann at Germany’s University of Göttingen and colleagues for creating the first detailed “weather map” of an exoplanet. The forecast for exoplanet WASP-127b is brutal with winds reaching 33,000 km/hr, which is much faster than winds found anywhere in the Solar System. The WASP-127b is a gas giant located about 520 light–years from Earth and the team used the CRIRES+ instrument on the European Southern Observatory’s Very Large Telescope to observe the exoplanet as it transited across its star in less than 7 h. Spectral analysis of the starlight that filtered through WASP-127b’s atmosphere revealed Doppler shifts caused by supersonic equatorial winds. By analysing the range of Doppler shifts, the team created a rough weather map of  WASP-127b, even though they could not resolve light coming from specific locations on the exoplanet. Nortmann and colleagues concluded that the exoplanet’s poles are cooler that the rest of WASP-127b, where temperatures can exceed 1000 °C. Water vapour was detected in the atmosphere, raising the possibility of exotic forms of rain.

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This episode of the Physics World Weekly podcast features Guangyu Zhang. Along with his colleagues at the Institute of Physics of the Chinese Academy of Sciences, Zhang has bagged the 2025 Physics World Breakthrough of the Year award for creating the first 2D metals.

In a wide-ranging conversation, we chat about the motivation behind the team’s research; the challenges in making 2D metals and how these were overcome; and how 2D metals could be used to boost our understanding of condensed matter physics and create new technologies.

I am also joined by my Physics World colleague Matin Durrani to talk about some of the exciting physics that we will be showcasing in 2025.

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Ever since the National Quantum Computing Centre was launched five years ago, its core mission has been to accelerate the pathway towards practical adoption of the technology. That has required technical innovation to scale up hardware platforms and create the software tools and algorithms needed to tackle real-world applications, but there has also been a strong focus on engaging with companies to build connections, provide access to quantum resources, and identify opportunities for deriving near-term value from quantum computing.

It makes sense, then, that the NQCC should form the cornerstone of a new Quantum Cluster at the Harwell Campus of Science and Innovation in Oxfordshire. The hope is that the NQCC’s technical expertise and infrastructure, combined with the services and facilities available on the wider Harwell Campus, will provide a magnet for new quantum start-ups as well as overseas companies that are seeking to establish a presence within the UK’s quantum ecosystem.

By accelerating collaboration across government, industry and academia, we will turn research excellence into industrial strength.

“We want to leverage the public investment that has been made into the NQCC to catalyse business growth and attract more investment into the UK’s quantum sector,” said Najwa Sidqi, manager of the Harwell Quantum Cluster, at the official launch event in November. “By accelerating collaboration across government, industry and academia, we will turn research excellence into industrial strength.”

The cluster, which has been ramping up its activities over the last year, is working to ambitious targets. Over the next decade the aim is to incubate at least 100 quantum companies on the Harwell site, create more than 1000 skilled jobs, and generate more than £1 billion of private and public investment. “Our aim is to build the foundations of a globally competitive quantum economy that delivers impact far beyond science and research,” added Sidqi.

Tangible evidence that the approach works is offered by the previous clustering activities on the Harwell Campus, notably the Space Cluster that has expanded rapidly since its launch in 2010. Anchored by the RAL Space national laboratory and bolstered by the presence of ESA and the UK Space Agency, the Space Cluster now comprises more than 100 organizations that range from small start-ups to the UK technology hubs of global heavyweights such as Airbus and Lockheed Martin.

More generally, the survival rate of start-up companies operating on the Harwell site is around 95%, compared with an average of around 50%. “At Harwell there is a high density of innovators sharing the same space, which generates more connections and more ideas,” said Julia Sutcliffe, Chief Scientific Advisor for the UK’s Department for Business and Trade. “It provides an incredible combination of world-class infrastructure and expertise, accelerating the innovation pathway and helping to create a low-risk environment for early-stage businesses and investors.”

The NQCC has already seeded that innovation activity through its early engagement with both quantum companies and end users of the technology. One major initiative has been the testbed programme, which has enabled the NQCC to invest £30m in seven hardware companies to deploy prototype quantum computers on the Harwell Campus. As well as providing access to operational systems based on all of the leading qubit modalities, the testbed programme has also provided an impetus for inward investment and job creation.

One clear example is provided by QuEra Computing, a US-based spin-off from Harvard University and the Massachusetts Institute of Technology that is developing a hardware platform based on neutral atoms. QuEra was one of the companies to win funding through the testbed programme, with the firm setting up a UK-based team to deploy its prototype system on the Harwell Campus. But the company could soon see the benefits of establishing a UK centre for technology development on the site. “Harwell is immensely helpful to us,” said Ed Durking, Corporate Director of QuEra Computing UK. “It’s a nucleus where we enjoy access to world-class talent, vendors, customers, and suppliers.”

On a practical level, establishing its UK headquarters on the Harwell Campus has provided QueEra with easy access to specialist contractors and services for fitting out and its laboratories. In June the company moved into a building that is fully equipped with flexible lab space for R&D and manufacturing, and since then the UK-based team has started to build the company’s most powerful quantum computer at the facility. Longer term, establishing a base within the UK could open the door to new collaborations and funding opportunities for QuEra to further develop its technology, with the company now focused on integrating full error correction into its neutral-atom platform by 2026.

Access to the world-class infrastructure on the Harwell Campus has benefitted the other testbed providers in different ways. For ORCA Computing, a UK company developing and manufacturing photonic quantum computers, the goal was to install a testbed system within Harwell’s high-performance computing centre rather than the NQCC’s experimental labs. “Our focus is to build commercial photonic quantum systems that can be integrated into conventional datacentres, enabling hybrid quantum-classical workflows for real-world applications,” explained Geoff Barnes, Head of Customer Success at ORCA. “Having the NQCC as an expert customer enabled us to demonstrate and validate our capabilities, building the system in our own facility and then deploying it within an operational environment.”

This process provided a valuable learning experience for the ORCA engineers. The experts at Harwell helped them to navigate the constraints of installing equipment within a live datacentre, while also providing practical assistance with the networking infrastructure. Now that the system is up and running, the Harwell site also provides ORCA with an open environment for showcasing its technology to prospective customers. “As well as delivering a testbed system to the NQCC, we can now demonstrate our platform to clients within a real-world setting,” added Barnes. “It has also been a critical step toward commercial deployment on our roadmap, enabling our partners to access our systems remotely for applications development.”

While the NQCC has already played a vital role in supporting companies as they make the transition towards commercialization, the Quantum Cluster has a wider remit to extend those efforts into other quantum technologies, such as sensing and communications, that are already finding real-world applications. It will also have a more specific focus on attracting new investment into the UK, and supporting the growth of companies that are transitioning from the start-up phase to establish larger scale commercial operations.

“In the UK we have traditionally been successful in creating spin-off activities from our strong research base, but it has been more challenging to generate the large capital investments needed to scale businesses in the technology sector,” commented Sidqi. “We want to strengthen that pipeline to ensure that the UK can translate its leadership in quantum research and early-stage innovation into long-term prosperity.”

To accelerate that process the Quantum Cluster announced a strategic partnership with Quantum Exponential, the first UK-based venture capital fund to be entirely focused on quantum technologies. Ian Pearson, the non-executive chairman of the Quantum Exponential, explained that the company is working to generate an investment fund of £100m by the end of 2027 that will support quantum companies as they commercialize their technologies and scale up their businesses. “Now is the time for investment into quantum sector,” said Pearson. “A specialist quantum fund with the expertise needed to analyse and price deals, and to do all the necessary due diligence, will attract more private investment that will help UK companies to grow and scale.”

Around two-thirds of the investments will be directed towards UK-based companies, and as part of the partnership Quantum Exponential will work with the Quantum Cluster to identify and support high-potential quantum businesses within the Harwell Campus. The Quantum Cluster will also play a crucial role in boosting investor confidence – particularly in the unique ability of the Harwell Campus to nurture successful technology businesses – and making connections with international innovation networks to provide UK-based companies with improved access to global markets.

“This new cluster strengthens our national capability and sends a clear signal to global investors that the UK is the place to develop and scale quantum technologies,” commented Michael Cuthbert, Director of the NQCC. “It will help to ensure that quantum innovation delivers benefits not just for science and industry, but for the economy and society as a whole.”

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An aerogel material that is more than 99% transparent to light and is an excellent thermal insulator has been developed by Ivan Smalyukh and colleagues at the University of Colorado Boulder in the US. Called MOCHI, the material can be manufactured in large slabs and could herald a major advance in energy-efficient windows.

While the insulating properties of building materials have steadily improved over the past decades, windows have consistently lagged behind. The problem is that current materials used in windows – mostly glass – have an inherent trade-off between insulating ability and optical transparency. This is addressed to some extent by using two or three layers of glass in double- and triple-glazed windows. However, windows remain the largest source of heat loss from most buildings.

A solution to the window problem could lie with aerogels in which the liquid component of a regular gel is replaced with air. This creates solid materials with networks of pores that make aerogels the lightest solid materials ever produced. If the solid component is a poor conductor of heat, then the aerogel will be an extremely good thermal insulator.

“Conventional aerogels, like the silica and cellulose based ones, are common candidates for transparent, thermally insulating materials,” Smalyukh explains. “However, their visible-range optical transparency is intrinsically limited by the scattering induced by their polydisperse pores – which can range from nanometres to micrometres in scale.”

Hazy appearance

While this problem can be overcome fairly easily in thin aerogel films, creating appropriately-sized pores on the scale of practical windows has so far proven much more difficult, leading to a hazy, translucent appearance.

Now, Smalyukh’s team has developed a new fabrication technique involving a removable template. Their approach hinges on the tendency of surfactant molecules called CPCL to self-assemble in water. Under carefully controlled conditions, the molecules spontaneously form networks of cylindrical tubes, called micelles. Once assembled, the aerogel precursor – a silicone material called polysiloxane – condenses around the micelles, freezing their structure in place.

“The ensuing networks of micelle-templated polysiloxane tubes could be then preserved upon the removal of surfactant, and replacing the fluid solvent with air,” Smalyukh describes. The end result was a consistent mesoporous structure, with pores ranging from 2–50 nm in diameter. This is too small to scatter visible light, but large enough to interfere with heat transport.

As a result, the mesoporous, optically clear heat insulator (MOCHI) maintains its transparency even when fabricated in slabs over 3 cm thick and a square metre in area. This suggests that it could be used to create practical windows.

High thermal performance

“We demonstrated thermal conductivity lower than that of still air, as well as an average light transmission above 99%,” Smalyukh says. “Therefore, MOCHI glass units can provide a similar rate of heat transfer to high-performing building roofs and walls, with thicknesses comparable to double pane windows.”

If rolled out on commercial scales, this could lead to entirely new ways to manage interior heating and cooling. According to the team’s calculations, a building retrofitted with MOCHI windows could boost its energy efficiency from around 6% (a typical value in current buildings) to over 30%, while reducing the heat energy passing through by around 50%.

With its ability to admit light while blocking heat transport, the researchers suggest that MOCHI could unlock entirely new functionalities for conventional windows. “Such transparent insulation also allows for efficient harnessing of thermal energy from unconcentrated solar radiation in different climate zones, promising the use of parts of opaque building envelopes as solar thermal energy generating panels,” Smalyukh adds.

The new material is described in Science.

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Errors are the bugbear of quantum computing, and they’re hard to avoid. While quantum computers derive their computational clout from the fact that their qubits can simultaneously court multiple values, the fragility of qubit states ramps up their error rates. Many research groups are therefore seeking to reduce or manage errors so they can increase the number of qubits without reducing the whole enterprise to gibberish.

A team at the US-based firm Atom Computing is now reporting substantial success in this area thanks to a multi-part strategy for keeping large numbers of qubits operational in quantum processors based on neutral atoms. “These capabilities allow for the execution of more complex, longer circuits that are not possible without them,” says Matt Norcia, one of the Atom Computing researchers behind this work.

While neutral atoms offer several advantages over other qubit types, they traditionally have significant drawbacks for one of the most common approaches to error correction. In this approach, some of the entangled qubits are set aside as so-called “ancillaries”, used for mid-circuit measurements that can indicate how a computation is going and what error correction interventions may be necessary.

In neutral-atom quantum computing, however, such interventions are generally destructive. Atoms that are not in their designated state are simply binned off – a profligate approach that makes it challenging to scale up atom-based computers. The tendency to discard atoms is particularly awkward because the traps that confine atoms are already prone to losing atoms, which introduces additional errors while reducing the number of atoms available for computations.

Reduce, re-use, replenish

As well as demonstrating protocols for performing measurements to detect errors in quantum circuits with little atom loss, the researchers at Atom Computing also showed they could re-use ancillary atoms – a double-pronged way of retaining more atoms for calculations. In addition, they demonstrated that they could replenish the register of atoms for the computation from a spatially separated stash in a magneto-optic trap without compromising the quantum state of the atoms already in the register.

Norcia says that these achievements — replacing atoms from a continuous source, while reducing the number of atoms needing replacement to begin with — are key to running computations without running out of atoms.  “To our knowledge, any useful quantum computations will require the execution of many layers of gates, which will not be possible unless the atom number can be maintained at a steady-state level throughout the computation,” he tells Physics World.

Cool and spaced out

Norcia and his collaborators at Microsoft Quantum, the Colorado School of Mines and Stanford University worked with ytterbium (Yb) atoms, which he describes as “natural qubits” since they have two ground states. A further advantage is that the transitions between these qubit states and other states used for imaging and cooling are weak, meaning the researchers could couple just one qubit state to these other states at a time. The team also leveraged a previously-developed approach for mid-circuit measurement that scatters light from only one qubit state and does not disturb the other, making it less destructive.

Still, Norcia tells Physics World, “the challenge was to re-use atoms, and key to this was cooling and performance.” To this end, they first had to shift the atoms undergoing mid-circuit measurements away from the atoms in the computational register, to avoid scattering laser light off the latter. They further avoided laser-related collateral damage by designing the register such that the measurement and cooling light was not at the resonant wavelength of the register atoms. Next, they demonstrated they could cool already-measured atoms for re-use in the calculation. Finally, they showed they could non-disruptively replenish these atoms with others from a magneto-optical trap positioned 300 nm below the tweezer arrays that held atoms for the computational register.

Mikhail Lukin, a physicist at Harvard University, US who has also worked on the challenges of atom loss and re-use in scalable, fault-tolerant neutral atom computing, has likewise recently reported successful atom re-use and diminished atom loss. Although Lukin’s work differs from that of the Atom Computing team in various ways – using rubidium instead of ytterbium atoms and a different approach for low atom loss mid-circuit measurements, for starters – he says that the work by Norcia and his team “represents an important technical advance for the Yb quantum computing platform, complementing major progress in the neutral atom quantum computing community in 2025”.

The research appears in Physical Review X.

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The latest episode of Physics World Stories takes you inside CUWiP+, the Conference for Undergraduate Women and Non-Binary Physicists, and the role the annual event plays in shaping early experiences of studying physics.

The episode features June McCombie from the University of Nottingham, who discusses what happens at CUWiP+ events and why they are so important for improving the retention of women and non-binary students in STEM. She reflects on how the conferences create space for students to explore career paths, build confidence and see themselves as part of the physics community.

Reflections and tips from CUWiP+ 2025

University of Birmingham students Tanshpreet Kaur and Harriett McCormick share their experiences of attending the 2025 CUWiP+ event at the University of Warwick and explain why they are excited for the next event, set for Birmingham, 19–22 March 2026. They describe standout moments from 2025, including being starstruck at meeting Dame Jocelyn Bell Burnell, who discovered radio pulsars in 1967.

The episode provides practical advice to get the most out of the event. Organizers design the programme to cater for all personalities – whether you thrive in lively, social situations, or prefer time to step back and reflect. Either way, CUWiP+ offers opportunities to be inspired and to make meaningful connections.

Hosted by Andrew Glester, the episode highlights how shared experiences and supportive networks can balance the often-solitary nature of studying physics, especially when you feel excluded from the majority group.

The post Forging a more inclusive new generation of physicists appeared first on Physics World.

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Quantum physics, kung-fu, LEGO and singing are probably not things you would normally put together. But that’s exactly what happened at this year’s Quantum Carousel.  

The event is a free variety show where incredible performers from across academia and industry converge for an evening of science communication. Held in Bristol, UK, on 14 November 2025, this was the second year the event was run – and once again it was entirely sold out.

As organizers, our goal was to bring together those involved in quantum and adjacent fields for an evening of learning and laughter. Each act was only seven minutes long and audience participation was encouraged, with questions saved for the dinner and drinks intervals.

The evening kicked off with a rousing speech and song from Chris Stewart, motivating the promotion of science communication and understanding. Felix Flicker related electron spin rotations to armlocks, with a terrific demonstration on volunteer Tony Short, while Michael Berry entertained us all with his eye-opening talk on how quantum physics has democratized music.  

PhD student double act Eesa Ali and Sebastien Bisdee then welcomed volunteers to the stage to see who could align a laser fastest. Maria Violaris expertly taught us the fundamentals of quantum error correction using LEGO.

Mike Shubrook explained the quantum thermodynamics of beer through stand-up comedy. And finally, John Rarity and his assistant Hugh Barrett (event co-organizer and co-author of this article) rounded off the night by demonstrating the magic of entanglement.  

Our event sponsors introduced the food and drinks portions of the evening, with Antonia Seymour (chief executive of IOP Publishing) and Matin Durrani (editor-in-chief of Physics World) opening the dinner interval, while Josh Silverstone (founder and chief executive of Hartley Ultrafast) kickstarted the networking drinks reception.  

Singing praises

Whether it was singing along to an acoustic guitar or rotating hands to emulate electron spin, everyone got involved, and feedback cited audience participation as a highlight.

“The event ran very smoothly, it was lots of fun and a great chance to network in a relaxed atmosphere,” said one attendee. Another added: “The atmosphere was really fun, and it was a really nice event to get loads of the quantum community together in an enjoyable setting.”

Appreciation of the atmosphere went both ways, with one speaker saying that their favourite part of the night was that “the audience was very inviting and easy to perform to”.  

Audience members also enjoyed developing a better understanding of the science that drives their industry. “I understood it and I don’t have any background in physics,” said one attendee. “I feel a marker of being a good scientist is being able to explain it in layperson’s terms.”

Reaching out

With the quantum community rapidly expanding, it needs people from a wide range of backgrounds such as computer science, engineering and business. Quantum Carousel was designed to strike a balance between high-level academic discussion and entertainment through entry-level talks, such as explaining error correction with props, or relating research to impact from stimulated emission to CDs.

By focusing on real-world analogies, these talks can help newcomers to develop an intuitive and memorable understanding. Meanwhile, those already in the field can equip themselves with new ways of communicating elements of their research. 

We look forward to hosting Quantum Carousel again in the future. We want to make it bigger and better, with an even greater range of diverse acts.

But if you’re interested in organizing a similar outreach event of your own, it helps to consider how you can create an environment that can best spark connections between both speakers and attendees. Consider your audience and how your event can attract different people for different reasons. In our case, this included the chance to network, engage with the performances, and enjoy the food and drink. 

• Quantum Carousel was founded by Zulekha Samiullah in 2024, and she and Hugh Barrett now co-lead the event. Quantum Carousel 2025 was sponsored by the QE-CDT, IOP Publishing and Hartley Ultrafast.

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What’s the research mission of the IBS Center for Van der Waals Quantum Solids (IBS-VdWQS)?

Our multidisciplinary team aims to create heteroepitaxial van der Waals quantum solids at system scales, where the crystal lattices and symmetries of these novel 2D materials are artificially moulded to atomic precision via epitaxial growth. Over time, we also hope to translate these new solids into quantum device platforms.

Clearly there’s all sorts of exotic materials physics within that remit.

Correct. We form van der Waals heterostructures by epitaxial manipulation of the crystal lattice in diverse, atomically thin 2D materials – for example, 2D heterostructures incorporating graphene, boron nitride or transition-metal dichalcogenides (such as MoS₂, WSe₂, NbSe₂, TaSe₂ and so on). Crucially, the material layers are held in place only by weak van der Waals forces and with no dangling chemical bonds in the direction normal to the layers.

These 2D layers can also be laterally “stitched” into hexagonal or honeycomb lattices, with the electronic and atomic motions confined into the atomic layers. Using state-of-the-art epitaxial techniques, our team can then artificially stack these lattices to form a new class of condensed matter with exotic interlayer couplings and emergent electronic, optical and magnetic properties – properties that, we hope, will find applications in next-generation quantum devices.

The IBS-VdWQS is part of Korea’s Institute for Basic Science (IBS). How does this arrangement work?

The IBS headquarters was established in 2011 as Korea’s first dedicated institute for fundamental science. It’s an umbrella organization coordinating the activity of 38 centres-of-excellence across the physical sciences, life sciences, as well as mathematics and data science. In this way, IBS specializes in long-range initiatives that require large groups of researchers from Korea and abroad.

Our IBS-VdWQS is a catalyst for advances in fundamental materials science and condensed-matter physics, essentially positioned as a central-government-funded research institution in a research-oriented university. Particularly important in this regard is our colocation on the campus of Pohang University of Science and Technology (POSTECH), one of Korea’s leading academic centres, and our adjacency to large-scale facilities like the Pohang Synchrotron Radiation Facility (PAL) and Pohang X-ray free-electron laser (PAL-XFEL). It’s worth noting as well that all the principal investigators (PIs) in our centre hold dual positions as IBS researchers and POSTECH professors.

So IBS is majoring on strategic research initiatives?

Absolutely – and that perspective also underpins our funding model. The IBS-VdWQS was launched in 2022 and is funded by IBS for an initial period through to 2032 (with a series of six-year extensions subject to the originality and impact of our research). As such, we are able to encourage autonomy across our 2D materials programme, giving scientists the academic freedom to pursue questions in basic research without the bureaucracy and overhead of endless grant proposals. Team members know that, with plenty of hard work and creativity, they have everything they need here to do great science and build their careers.

Your core remit is fundamental science, but what technologies could eventually emerge from the IBS-VdWQS research programme?

While the focus is very much on basic science, epitaxial scalability is hard-wired into all our lines of enquiry. In short: we are creating new 2D materials via epitaxial growth and this ultimately opens a pathway to wafer-scale industrial production of van der Waals materials with commercially interesting semiconducting, superconducting or emergent properties in general.

Right now, we are investigating van der Waals semiconductors and the potential integration of MoS₂ and WSe₂ with silicon for new generations of low-power logic circuitry. On a longer timeline, we are developing new types of high-Tc (around 10 K) van der Waals superconductors for applications in Josephson junctions, which are core building blocks in superconducting quantum computers.

There’s a parallel opportunity in photonic quantum computing, with van der Waals materials shaping up as promising candidates for quantum light-emitters that generate on-demand (deterministic) and highly coherent (indistinguishable) single-photon streams.

Establishing a new research centre from scratch can’t have been easy. How are things progressing?

It’s been a busy three years since the launch of the IBS-VdWQS. The most important task at the outset was centralization – pulling together previously scattered resources, equipment and staff from around the POSTECH campus. We completed the move into our purpose-built facility, next door to the PAL synchrotron light source, at the end of last year and have now established dedicated laboratory areas for the van der Waals Epitaxy Division; Quantum Device and Optics Division; Quantum Device Fabrication Division; and the Imaging and Spectroscopy Division.

One of our front-line research efforts is building a van der Waals Quantum Solid Cluster, an integrated system of multiple instruments connected by ultra-high-vacuum lines to maintain atomically clean surfaces. We believe this advanced capability will allow us to reliably study air-sensitive van der Waals materials and open up opportunities to discover new physics in previously inaccessible van der Waals platforms.

Are there plans to scale the IBS-VdWQS work programme?

Right now, my priority is to promote opportunities for graduate students, postdoctoral researchers and research fellows to accelerate the centre’s expanding research brief. Diversity is strength, so I’m especially keen to encourage more in-bound applications from talented experimental and theoretical physicists in Europe and North America. Our current research cohort comprises 30+ PhD students, seven postdocs (from the US, India, China and Korea) and seven PIs.

Over the next five years, we aim to scale up to 25+ postdocs and research fellows and push out in new directions such as scalable quantum devices. In particular, we are looking for scientists with specialist know-how and expertise in areas like materials synthesis, quantum transport, optical spectroscopy and scanning probe microscopy (SPM) to accelerate our materials research.

How do you support your early-career researchers at IBS-VdWQS?

We are committed to nurturing global early-career talent and provide a clear development pathway from PhD through postdoctoral studies to student research fellow and research fellow/PI. Our current staff PIs have diverse academic backgrounds – materials science, physics, electronic engineering and chemistry – and we therefore allow early-career scientists to have a nominated co-adviser alongside their main PI. This model means research students learn in an integrated fashion that encourages a “multidisciplinarian” mindset – majoring in epitaxial growth, low-temperature electronic devices and optical spectroscopy, say, while also maintaining a watching brief (through their co-adviser) on the latest advances in materials characterization and analysis.

What does success look like at the end of the current funding cycle?

With 2032 as the first milestone year in this budget cycle, we are working to establish a global hub for van der Waals materials science – a highly collaborative and integrated research programme spanning advanced fabrication, materials characterization/analysis and theoretical studies. More capacity, more research infrastructure, more international scientists are all key to delivering our development roadmap for 2D semiconductor and superconductor integration towards scalable, next-generation low-power electronics and quantum computing devices.

• Find more information on open research positions at IBS-VdWQS.

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Atoms in a one-dimensional quantum gas behave like a Newton’s cradle toy, transferring energy from atom to atom without dissipation. Developed by researchers at the TU Wien, Austria, this quantum fluid of ultracold, confined rubidium atoms can be used to simulate more complex solid-state systems. By measuring transport quantities within this “perfect” atomic system, the team hope to obtain a deeper understanding of how transport phenomena and thermodynamics behave at the quantum level.

Physical systems transport energy, charge and mass in various ways. Electrical currents streaming along a wire, heat flowing through a solid and light travelling down an optical fibre are just three examples. How easily these quantities move inside a material depends on the resistance they experience, with collisions and friction slowing them down and making them fade away. This level of resistance largely determines whether the material is classed as an insulator, a conductor or a superconductor.

The mechanisms behind such transport fall into two main categories. The first is ballistic transport, which features linear movement without loss, like a bullet travelling in a straight line. The second is diffusive transport, where the quantity is subject to many random collisions. A good example is heat conduction, where the heat moves through a material gradually, travelling in many directions at once.

Breaking the rules

Most systems are strongly affected by diffusion, which makes it surprising that the TU Wien researchers could build an atomic system where mass and energy flowed freely without it. According to study leader Frederik Møller, the key to this unusual behaviour is the magnetic and optical fields that keep the rubidium atoms confined to one dimension, “freezing out” interactions in the atoms’ two transverse directions.

Because the atoms can only move along a single direction, Møller explains, they transfer momentum perfectly, without scattering their energy as would be the case in normal matter. Consequently, the 1D atomic system does not thermalize despite being subject to thousands of collisions.

To quantify the transport of mass (charge) and energy within this system, the researchers measured quantities known as Drude weights, which are fundamental parameters that describe ballistic, dissipationless transport in solid-state environments. According to these measurements, the single-dimensional interacting bosonic atoms do indeed demonstrate perfect dissipationless transport. The results also agree with the generalized hydrodynamics (GHD) theoretical framework, which describes the large-scale, inhomogeneous dynamics of one-dimensional integrable quantum many-body systems such as ultracold atomic gases or specific spin chains.

A Newton’s cradle for atoms

According to team leader Jörg Schmiedmayer, the experiment is analogous to a Newton’s cradle toy, which consists of a row of metal balls suspended on wires (see below). When the ball on one end of the row is made to collide with the one next to it, its momentum transfers straight through the other balls to the ball on the opposite end, which swings out. Schmiedmayer adds that the system makes it possible to study transport under perfectly controlled conditions and could open new ways of understanding how resistance emerges, or disappears, at the quantum level. “Our next steps are applying the method to strongly correlated transport and to transport in a topological fluid,” he tells Physics World.

 

Karèn Kheruntsyan, a theoretical physicist at the University of Queensland, Australia, who was not involved in this research, calls it “a significant step for studying quantum transport”. He says the team’s work clearly demonstrates ballistic (dissipationless) transport at a finite temperature, providing an experimental benchmark for theories of integrability and disorder. The work also validates the thermodynamic meaning of Drude weights, while confirming that linear-response theory and GHD accurately describe transport in quantum systems.

In Kheruntsyan’s view, though, the team’s biggest achievement is the quantitative extraction of Drude weights that characterize atomic and energy currents, with “excellent agreement” between experiment and theory. This, he says, shows truly ballistic transport in an interacting many-body system. One caveat, though, is that the system’s limited spatial resolution and near-ideal integrability prevent it from being used to explore diffusive regimes or stronger interaction effects, leaving microscopic dynamics such as dispersive shock waves unresolved.

The study is published in Science.

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Physics students from under-represented groups consistently report a lower sense of belonging at university than their over-represented peers. These students experience specific challenges that make them feel undervalued and excluded. Yet a strong sense of belonging has been shown to lead to improved academic performance, greater engagement in courses and better mental wellbeing. It is vital, then, that universities make changes to help eliminate these challenges.

Students are uniquely placed to describe the issues when it comes to belonging in physics. With this mind, as an undergraduate physics student with a passion for making the discipline more diverse and inclusive, I conducted focus groups with current and former physics students, interviewed experts and performed an analysis of current literature.  This was part of a summer project funded by the Royal Institution and is currently being finalized for publication.

From this work it became clear that under-represented groups face many challenges to developing a strong sense of belonging in physics, but, at the same time, there are ways to improve the everyday experiences of students. When it comes to barriers, one is the widely held belief – reflected in the way physicists are depicted in the media and textbooks – that you need to be a “natural genius” to succeed in university physics. This notion hampers students from under-represented groups, who see peers from the over-represented majority appearing to grasp concepts more quickly and lecturers suggesting certain topics are “easy”.

The feeling that physics demands natural ability also arises from the so-called “weed out” culture, which is defined as courses that are intentionally designed to filter students out, reduce class sizes and diminish sense of belonging. Students who we surveyed believe that the high fail rate is caused by a disconnect between the teaching and workshops on the course and the final exam.

A third cause of this perception that you need some innate ability to succeed in physics is the attitudes and behaviour of some professors, lecturers and demonstrators. This includes casual sexist and racist behaviour; belittling students who ask for help; and acting as if they’re uninterested in teaching. Students from under-represented groups report significantly lower levels of respect and recognition from instructors, which damages their resilience and weakens sense of belonging.

Students from under-represented groups are also more likely to be isolated from their class mates and feel socially excluded from them. This means they lack a support network, leaving them with no-one to turn to when they encounter challenges. Outside the lecture theatre, students from under-represented groups typically face many microaggressions in their day-to-day university experience. These are subtle indignities or insults, unconsciously or consciously, towards minorities such as people of colour being told they “speak English very well”, male students refusing to accept women’s ideas, and the assumption that gender minorities will take on administrative roles in group projects.

Focus on the future

So what can be done? The good news is that there are many solutions to mitigate these issues and improve a sense of belonging. First, institutions should place more emphasis on small group “active learning” – which includes discussions, problem solving and peer-based learning. These pedagogical strategies have been shown to boost belonging, particularly for female students. After these active-learning sessions, non-academic, culturally sensitive social lunches can help turn “course friends” to “real friends” who choose to meet socially and can become a support network. This can help build connections within and between degree cohorts.

Another solution is for universities to invite former students to speak about their sense of belonging and how it evolved or improved throughout their degree. Hearing about struggles and learning tried-and-tested strategies to improve resilience can help students better prepare for stressful situations. Alumni are more relatable than generic messaging from the university wellbeing team.

Building closer links between students and staff also enhances a sense of belonging. It helps humanise lecturers and demonstrate that staff care about student wellbeing and success. This should be implemented by recognizing staff efforts formally so that the service roles of faculty members are formally recognized and professionalized.

Universities should also focus on hiring more diverse teaching staff, who can serve as role models, using their experiences to relate to and engage with under-represented students. Students will end up feeling more embedded within the physics community, improving both their sense of belonging and performance.

One practical way to increase diversity in hiring is for institutions to re-evaluate what they value. While securing large grants is valuable, so is advocating for equality, diversity and inclusion; public engagement; and the ability to inspire the next generation of physicists.

Another approach is to establish “departmental action teams” to find tailored solutions to unite undergraduates, postgraduates, teaching and research staff. Such teams identify issues specific to their particular university, and they can gather data through surveying the department to identify trends and recommend practical changes to boost belonging.

Implementing these measures will not only improve the sense of belonging for students from under-represented groups but also cultivate a more inclusive, diverse physics workforce. That in turn will boost the overall research culture, opening up research directions that may have previously been overlooked, and yielding stronger scientific outputs. It is crucial that we do more to support physics students from under-represented groups to create a more diverse physics community. Ultimately, it will benefit physics and society as a whole.

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The gyromagnetic ratio is the ratio of a particle’s magnetic moment and its angular momentum. This value determines how a particle responds to a magnetic field. According to classical physics, muons should have a gyromagnetic ratio equal to 2. However, owing to quantum mechanics, there is a small difference between the expected gyromagnetic ratio and the observed value. This discrepancy is known as the anomalous magnetic moment.

The anomalous magnetic moment is incredibly sensitive to quantum fluctuations. It can be used to test the Standard Model of physics, and previous consistent experimental discrepancies have hinted at new physics beyond the Standard Model. The search for the anomalous magnetic moment is one of the most precise tests in modern physics.

To calculate the anomalous magnetic moment, experiments such as Fermilab’s Muon g-2 experiment have been set up where researchers measure the muon’s wobble frequency, which is caused by its magnetic moment. But effects such as hadronic vacuum polarization and hadronic light-by-light scattering cause uncertainty in the measurement. Unlike hadronic vacuum polarization, hadronic light-by-light cannot be directly extracted from experimental cross-section data, making it dependent on the model used and a significant computational challenge.

In this work, the researcher took a major step in resolving the anomalous magnetic moment of the muon. Their method calculated how the neutral pion contributes to hadronic light-by-light scattering, used domain wall fermions to preserve symmetry, employed eight different lattice configurations with variational pion masses, and introduced a pion structure function to find the key contributions in a model-independent method. The pion transition form factor was computed directly at arbitrary space-like photon momenta, and a Gegenbauer expansion was used to confirm that about 98% of the π⁰-pole contribution was determined in a model-independent way. The analysis also included finite-volume corrections and chiral and continuum extrapolations and yielded a value for the π⁰ decay width.

The development of a more accurate and model-independent anomalous magnetic moment for the muon has reduced major theoretical uncertainties and can make Standard Model precision tests more robust.

Do you want to learn more about this topic?

The muon Smasher’s guide Hind Al Ali et al (2022)

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