From squirting cucumbers to cosmic stamps, physics has had its fair share of quirky stories this year. Here is our pick of the best 10, not in any particular order.

Escape from quantum physics

Staff at the clunkily titled Dresden-Würzburg Cluster of Excellence for Complexity and Topology in Quantum Matter (ct.qmat) had already created a mobile phone app “escape room” to teach children about quantum mechanics. But this year the app became reality at Dresden’s science museum. Billed as “Germany’s first quantum physics escape room”, the Kitty Q Escape Room has four separate rooms and 17 puzzles that offer visitors a multisensory experience that explores the quirky world of quantum mechanics. The goal for participants is to discover if Kitty Q – an imaginary being that embodies the spirit of Schrödinger’s cat – is dead or alive. Billed as being “perfect for family outings, children’s birthday parties and school field trips”, the escape room “embraces modern gamification techniques”, according to ct.qmat physicist Matthias Vojuta, “We ensure that learning happens in an engaging and subtle way,” he says. “The best part [is] you don’t need to be a maths or physics expert to enjoy the game.

Corking research

Coffee might be the drink of choice for physicists, but when it comes to studying the fascinating physics of liquids, champagne is hard to beat. That’s mostly because of the huge pressures inside the bottle and the explosion of bubbles that are released once the cork is removed. Experiments have already examined the expanding gas jet that propels the cork stopper out of a just-opened bottle caused by the radiation of shock waves up the neck. Now physicists in Austria have looked at the theory of how these supersonic waves move. The “Mach disc” that forms just outside the bottle opening is, they found, convex and travels away from the bottle opening before moving back towards it. A second Mach disc then forms when the first disc moves back although it’s not clear if this splits from the first or is a distinct disc. Measuring the distance of the Mach disc from the bottle also provides a way to determine the gas pressure or temperature in the champagne bottle.

Cosmic stamps

We love a good physics or astronomy stamp here at Physics World and this year’s offering from the US Postal Service didn’t disappoint. In January, they released two stamps to mark the success of NASA’s James Webb Space Telescope (JWST), which took off in 2021. The first features an image taken by the JWST’s Near-Infrared Camera of the “Cosmic Cliffs” in the Carina Nebula, located about 7600 light-years from Earth. The other stamp has an image of the iconic Pillars of Creation within the vast Eagle Nebula, which lies 6500 light-years away that was captured by the JWST’s Mid-Infrared Instrument. “With these stamps, people across the country can have their own snapshot of Webb’s captivating images at their fingertips,” noted NASA’s head of science, the British-born physicist Nicola Fox.

Record-breaking cicadas

This year marked the first time in more than 200 years that two broods belonging to two species of cicadas emerged at the same time. And the cacophony that the insects are famous for wasn’t the only aspect to watch out for. Researchers at Georgia Tech in the US examined another strange aspect of these creatures – how they wee. We know that most insects urinate via droplets as this is more energy efficient than emitting a stream of liquid. But cicadas are such voracious eaters of tree sap that individually flicking each drop away would be too taxing. To get around this problem, cicadas (just as we do) eject the pee via a jet, which the Georgia Tech scientists looked at for the first time. “Previously, it was understood that if a small animal wants to eject jets of water, then this [is] challenging, because the animal expends more energy to force the fluid’s exit at a higher speed,” says Elio Challita, who is based at Harvard University. “This is due to surface tension and viscous forces. But a larger animal can rely on gravity and inertial forces to pee.” According to the team, cicadas are the smallest animal to create such high-speed jets – a finding that could, say the researchers, lead to the design of better nozzles and robots. 

Raising the bar

Machine learning was a big topic this year thanks to the 2024 Nobel prizes for both physics and chemistry. Not to be outdone, scientists from Belgium announced they had used machine-learning algorithms to predict the taste and quality of beer and what compounds brewers could use to improve the flavour of certain tipples. Kevin Verstrepen from KU Leuven and colleagues spent five years characterizing over 200 chemical properties from 250 Belgian commercial beers across 22 different styles, such as Blond and Tripel beers. They also gathered tasting notes from a panel of 15 people and from the RateBeer online beer review database. A machine-learning model that was trained on the data could predict the flavour and score of the beers using just the beverages’ chemical profile. By adding certain aromas predicted by the model, the team was even able to boost the quality – as determined by blind tasting – of existing commercial Belgian ale. The scientists hope the findings could be used to improve alcohol-free beer. Yet KU Leuven researcher Michiel Scheurs admits that they did celebrate the work “with the alcohol-containing variants”.

Beetling away

Whirligig beetles can reach speeds of up to 1m/s – or 100 body lengths per second – as they skirt across the water. Scientists thought the animals did this using their oar-like hind legs to generate “drag-based” thrust, a bit like how a rodent swims. To do so, however, the beetle would need to move its legs faster than its swimming speed, which in turn would require pushing against the water at unrealistic speeds. To solve this bugging problem, researchers at Cornell University used high-speed cameras to film the whirligigs as they swam. They found that the beetles instead use lift-based thrust, which has been documented in whales, dolphins and sea lions. The thrusting motion is perpendicular to the water surface and the researchers calculate that the forces generated by the beetle in this way can explain their speedy movements in the water. According to Cornell’s Yukun Sun, that makes whirligig beetles “by far the smallest organism to use lift-based thrust for swimming”.

Pistachio packing problem

It sounds like a question you might get in an exam: if you have a full bowl of N pistachios, what size container do you need for the leftover 2N non-edible shells? Given that pistachios come in different shapes and sizes and the shells are non-symmetric, the problem’s a tougher nut to crack than you might think. Thankfully, the secret of pistachio-packing was  revealed in a series of experiments by physicists Ruben Zakine and Michael Benzaquen from École Polytechnique in Palaiseau, France. After placing 613 pistachios in a two-litre cylinder, they found that the container holding the shells needs to be just over half the size of the original pistachio bowl for well-packed nuts and three-quarters for loosely packed pistachios. Zakine and Benzaquen say that numerical simulations could be carried out to compare with the experimental findings and that the work extends beyond just nuts. “Our analysis can be relevant in other situations, for instance to determine the optimal container needed [for] mussel or oyster shells after a Pantagruelian seafood diner,” they claim

The physics of paper cuts

If you’ve ever been on the receiving end of a paper cut, you’ll know how painful it can be. To find out why paper is able to slice through skin so well, Kaare Jensen – a physicist from the Technical University of Denmark – and colleagues carried out a series of experiments using paper with a range of thicknesses to make incisions into a piece of gelatine at various angles. When combined with modelling, they discovered that paper cuts are a competition between slicing and “buckling”. Thin paper with a thickness of about 30microns doesn’t cut skin so well because it buckles – a mechanical instability that happens when a slender object like paper is compressed. But thick paper (above about 200microns) is poor at making an incision because it distributes the load over a greater area, resulting in only small indentations. The team discovered, however, that there is a paper cut “sweet spot” at around 65microns, which just happens to be close to the paper thickness used in print magazines. The researchers have now put their findings to use, creating a 3D-printed scalpel that uses scrap paper for the cutting edge. Dubbed a “papermachete”, it can slice through apple, banana peel, cucumber and even chicken. “Studying the physics of paper cuts has revealed a surprising potential use for paper in the digital age: not as a means of information dissemination and storage, but rather as a tool of destruction,” the researchers write.

Squirting cucumbers

The plant kingdom is full of intriguing ways to distribute seeds such as the dandelion pappus effortlessly, drifting on air currents. Not to be outdone, the squirting cucumber (Ecballium elaterium), which is native to the Mediterranean and is often regarded as a weed, has its own unique way of ejecting seeds. When ripe, the ovoid-shaped fruits detach from the stem and as it does so explosively ejects seeds in a high-pressure jet of mucilage. The process, which lasts just 30 ms, launches the seeds at more than 20 m/s with some landing 10 m away. Researchers in the UK revealed the mechanism behind the squirt for the first time by using high-speed imaging and mathematical modelling. The researchers found that in the weeks leading up to the ejection, fluid builds up inside the fruits so they become pressurized. Then just before seed dispersal, some of this fluid moves from the fruit to the stem, making it longer and stiffer. This process crucially causes the fruit to rotate from being vertical to close to an angle of 45°, improving the launch angle for the seeds. During the first milliseconds of ejection, the tip of the stem holding the fruit then recoils away causing the pod to counter-rotate and detach. As it does so, the pressure inside the fruit causes the seeds to eject at high speed. By changing parameters in the model, such as the stiffness of the stem, reveals that the mechanism has been fine-tuned to ensure optimal seed dispersal.

Chimp Shakespeare

And finally, according to the infinite monkeys theorem, a monkey randomly pressing keys on a typewriter for an infinite amount of time would eventually type out the complete works of William Shakespeare purely by chance. Yet analysis by two mathematicians in Australia found that even a troop might not have time to do so within the supposed timeframe of the universe. The researchers came to their conclusion after creating a computational model that assumed a constant chimpanzee population of 200 000, each typing at one key per second until the end of the universe in about 10¹⁰⁰ years. If that is true, there’d be only a 5% chance a single monkey would type “bananas” within its own lifetime of just over 30 years. But even all the chimps feverishly typing away couldn’t produce Shakespeare’s entire works (coming in at over 850 000 words) before the universe ends. “It is not plausible that, even with improved typing speeds or an increase in chimpanzee populations, monkey labour will ever be a viable tool for developing non-trivial written works,”  the authors conclude, adding that while the infinite monkeys theorem is true, it is also “somewhat misleading”, or in reality it’s “not to be”.

You can be sure that next year will throw up its fair share of quirky stories from the world of physics. See you next year!

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The past few years have seen several missions to the Moon and that continued in 2024. Yet things didn’t get off to a perfect start. In 2023, the Japanese Space Agency, JAXA, launched its Smart Lander for Investigating Moon (SLIM) mission to the Moon. Yet when it landed in January, it did so upside down. Despite that slight mishap, Japan still became the fifth nation to successfully soft land a craft on the Moon, following the US, Soviet Union, China and India.

In February, meanwhile, US firm Intuitive Machines achieved a significant milestone when it became the first private mission to soft land on the Moon. Its Odysseus mission touched down on the Moon’s Malapert A region, a small crater about 300 km from the lunar south pole. In doing so it also became the first US mission to make a soft landing on the Moon since Apollo 17 in December 1972.

Another significant lunar first came later in the year when China’s Chang’e-6 mission successfully returned samples back to Earth from the Moon’s far side. The feat made it into our top 10 breakthroughs for this year.

Amateur radio astronomers

Astronomy is unique in having a significant amateur community and while radio astronomy emerged from amateur beginnings, it is now the focus of elite, international global consortia. In this fascinating feature, astrophysicist and amateur radio astronomer Emma Chapman from the University of Nottingham, UK, outlined how the subject developed and why it needs to strike a fine balance between its science and engineering roots. And also make sure not to miss Chapman discussing the history of radio astronomy on the Physics World Stories podcast.

Hidden stories

Still on the podcast front, this Physics World Stories podcast from this year features a fascinating chat with astronaut Eileen Collins, who shared her extraordinary journey as the first woman to pilot and command a spacecraft. In the process, she broke several barriers in space exploration and inspired generations with her courage and commitment to discovery.

Euclid’s spectacular images

Astronomy and spectacular images go hand in hand and this year didn’t disappoint. While the James Webb Space Telescope continued to amaze, in May the European Space Agency released five spectacular images of the cosmos along with 10 scientific papers as part of Euclid’s early release observations. Euclid’s next data release will focus on its primary science objectives and is currently slated for March 2025, so keep an eye out for those next year.

The quest for dark matter

And finally, in the search for a cosmological model that perfectly explains our universe, most astronomers invoke the notion of dark matter. But what if they should instead modify the age-old laws of gravity? This year Physics World published the first articles of a three-part series, in which science writer Keith Cooper  looked at the struggles and successes of modified gravity in explaining phenomena at varying galactic scales as well as matching observations from the cosmic microwave background. In his second piece, Cooper explored some of dark matter’s recent successes and the serious challenges it is also facing.  Look out for the final article in this three-part series next year.

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What makes a physics story popular? The answer is partly hidden in the depths of Internet search algorithms, but it’s possible to discern a few trends in this list of the 10 most read stories published on the Physics World website in 2024. Well, one trend, at least: it seems that many of you really, really like stories about quantum physics. Happily, we’ll be publishing lots more of them in 2025, the International Year of Quantum Science and Technology. But in the meantime, here are 2024’s most popular stories – quantum and otherwise.

10. A quantum thought experiment that continues to confound

As main characters in quantum thought experiments go, Wigner’s friend isn’t nearly as well-known as Schrödinger’s cat. While the alive-or-dead feline was popularized in the mid-20^th century by the science fiction and fantasy writer Ursula K LeGuin, Wigner and his best mate remain relatively obscure, and unlikely to appear in an image created with entangled light (more on this later). Still, there’s plenty to ponder in this lesser-known thought experiment, which provocatively suggests that in the quantum world, what’s true may depend, quite literally, on where you stand: with Wigner’s friend inside a lab performing the quantum experiment, or with Wigner outside it awaiting the results.

9. A record-breaking superconductor that wasn’t

Popularity isn’t everything. This story focused on a paper about a high-temperature superconducting wire that appeared to have a current density 10 times higher than any previously reported. Unfortunately, the paper’s authors made an error when converting the magnetic units they used to calculate current density. This error – which the authors acknowledged, leading to the paper’s retraction – meant that the current density was too high by… well, by a factor of 10, actually.

Surprisingly, this wasn’t the most blatant factor-of-10 flop to enter the scientific literature this year. That dubious honour belongs to a team of environmental chemists who multiplied 60 kg x 7000 nanograms/kg to calculate the maximum daily dose of potentially harmful chemicals, and got an answer of…42 000 nanograms. Oops.

8. Exploiting quantum entanglement to create hidden images

Remember the entangled-light Schrödinger’s cat image? Well, here it is again, this time in its original context. In an experiment that made it onto our list of the top 10 breakthroughs of 2024, researchers in France used quantum correlations to encode an image into light such that the image only becomes visible when particles of light (photons) are observed by a single-photon sensitive camera. Otherwise, the image is hidden from view. It’s a neat result, and we’re glad you agree it’s worth reading about.

7. An icy exoplanet with an atmosphere

At this time of year, some of us in the Northern Hemisphere feel like we’re inhabiting an icy exoplanet already, and some of you experiencing Southern Hemisphere heat waves probably wish you were. Sadly, none of us is ever going to live on (or even visit) the temperate exoplanet LHS 1140 b, which is located 49 light-years away from Earth and has a mass 5.6 times larger. Still, astronomers think this watery, icy world could be only the third planet (after Earth and Mars) in its star’s habitable zone known to have an atmosphere, and that was enough to pique readers’ interest.

6. Vortex cannon generates toroidal electromagnetic pulses

An electromagnetic vortex cannon might sound like an accessory from Star Trek. In fact, it’s a real object made from a device called a horn microwave antenna. It gets its name because it generates an electromagnetic field in free space that rotates around the propagation direction of the wave structure, similar to how an air cannon blows out smoke rings. According to its inventors, the electromagnetic vortex cannon could be used to develop communication, sensing, detection and metrology systems that overcome the limitations of existing wireless applications.

5. Why our world (still) cannot be anything but quantum

Returning to the quantum theme, the fifth-most-read story of 2024 concerned an experiment that demonstrated a new violation of the Leggett-Garg inequality (LGI). While the better-known Bell’s inequality describes how the behaviour of one object relates to that of another object with which it is entangled, the conceptually similar LGI describes how the state of a single object varies at different points in time. If either inequality is violated, the world is quantum. Previous experiments had already observed LGI violations in several quantum systems, but this one showed, for the first time, that neutrons in a beam must be in a coherent superposition of states – a fundamental property of quantum mechanics.

4. ‘Hidden’ citations conceal the true impact of scientific research

When a scientific paper introduces a concept that goes on to become common knowledge, you might expect later researchers to cite the living daylights out of it – and you would be wrong. According to the study described in this article, the ideas in many such papers become so well known that the opposite happens: no-one bothers to cite them anymore.

This means that purely citation-based metrics of research “impact” tend to underestimate the importance of seminal works such as Alan Guth’s 1981 paper that introduced the theory of cosmic inflation. So if your amazing paper isn’t getting the citation love it deserves, take heart: maybe it’s too foundational for its own good.

3. Unifying gravity and quantum mechanics without the need for quantum gravity

Physicists have been trying to produce a theory that incorporates both gravity and quantum mechanics for almost a century now. One of the sticking points is that we don’t really know what a quantum theory of gravity might look like. Presumably, it would have to combine the world of gravity (where space and time warp in the presence of massive objects) with the world of quantum mechanics (which assumes that space and time are fixed) – but how?

For the University College London theorist Jonathan Oppenheim, this is the wrong question. As this article explains, Oppenheim has developed a new theoretical framework that aims to unify quantum mechanics and classical gravity – but, crucially, without the need to define a theory of quantum gravity first.

2. Open problem in quantum entanglement theory solved after nearly 25 years

Can a quantum system remain maximally entangled in a noisy environment? According to Julio I de Vicente from the Universidad Carlos III de Madrid, Spain, the answer is “no”. While the question and its answer might seem rather esoteric, this article explains that the implications extend beyond theoretical physics, with so-called “maximally entangled mixed states” having the potential to revolutionize our approach to other problems in quantum mechanics.

1. The ‘magic’ of quantum computation

The science fiction writer Arthur C Clarke famously said that “Any sufficiently advanced technology is indistinguishable from magic.” Sadly for Clarke fans, the magic in this article doesn’t involve physicists chanting incantations or waving wands over their experiments. Instead, it refers to quantum states that are especially hard to simulate on classical machines. These so-called “magic” states are a resource for quantum computers, and the amount of them available is a measure of a system’s quantum computational power. Indeed, certain error-correcting codes can improve the quality of magic states in a system, which makes a pleasing connection between this, the most-read article of 2024 on the Physics World website, and our pick for 2024’s “Breakthrough of the year.” See you in 2025!

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This year marked the 70th anniversary of the European Council for Nuclear Research, which is known universally as CERN. To celebrate, we have published a bumper crop of articles on particle and nuclear physics in 2024. Many focus on people and my favourite articles have definitely skewed in that direction. So let’s start with the remarkable life of accelerator pioneer Bruno Touschek.

Bruno Touschek: the physicist who escaped the Nazi Holocaust to build particle colliders

Born in Vienna in 1921 to a Jewish mother, Bruno Touschek’s life changed when Nazi Germany annexed Austria in 1938. After suffering antisemitism in his hometown and then in Rome, he inexplicably turned down an offer to study in the UK and settled in Germany. There he worked on a “death ray” for the military but was eventually imprisoned by the German secret police. He was then left for dead during a forced march to a concentration camp in 1945. When the war ended a few weeks later, Touschek’s expertise came to the attention of the British, who occupied north-western Germany. He went on to become a leading accelerator physicist and you can read much more about the extraordinary life of Touschek in this article by the physicist and biographer Giulia Pancheri.

Nuclear clock ticks ever closer

Today, the best atomic clocks would only be off by about 10 ms after running for the current age of the universe. But, could these timekeepers soon be upstaged by clocks that use a nuclear, rather than an atomic transition? Such nuclear clocks could rival their atomic cousins when it comes to precision and accuracy. They also promise to be fully solid-state, which means that they could be used in a wide range of commercial applications. This year saw physicists make new measurements and develop new technologies that could soon make nuclear clocks a reality. Click on the headline above to discover how physicists in the US have fabricated all of the components needed to create a nuclear clock made from thorium-229. Also, earlier this year physicists in Germany and Austria showed that they can put nuclei of the isotope into a low-lying metastable state that could be used in a nuclear clock. You can find out more here: “Excitation of thorium-229 brings a working nuclear clock closer”.

Physics World Live: the future of particle physics

In 2024 we launched our Physics World Live series of panel discussions. In September, we explored the future of particle physics with Tara Shears of the UK’s University of Liverpool, Phil Burrows at the University of Oxford in the UK and Tulika Bose at the University of Wisconsin–Madison in the US. Moderated by Physics World’s Michael Banks, the discussion focussed on next-generation particle colliders and how they could unravel the mysteries of the Higgs boson and probe beyond the Standard Model of particle physics. You can watch a video of the event by clicking on the above headline (free registration) or read an article based on the discussion here: “How a next-generation particle collider could unravel the mysteries of the Higgs boson”.

‘Sometimes nature will surprise us.’ Juan Pedro Ochoa-Ricoux on eureka moments and the future of neutrino physics

Neutrinos do not fit in nicely with the Standard Model of particle physics because of their non-zero masses. As a result some physicists believe that they offer a unique opportunity to do experiments that could reveal new physics. In a wide-ranging interview, the particle physicist Juan Pedro Ochoa-Ricoux explains why he has devoted much of his career to the study of these elusive subatomic particles. He also looks forward to two big future experiments – JUNO and DUNE – which could change our understanding of the universe.

Using Minecraft to get young people interested in particle physics: Çiğdem İşsever on the importance of science in the early years

“Children decide quite early in their life, as early as primary school, if science is for them or not,” explains Çiğdem İşsever – who is leads the particle physics group at DESY in Hamburg, and the experimental high-energy physics group at the Humboldt University of Berlin. İşsever has joined forces with physicists Steven Worm and Becky Parker to create ATLAScraft, which creates a virtual version of CERN’s ATLAS detector in the hugely popular computer game Minecraft. In this profile, the science writer Rob Lea talks to İşsever about her passion for outreach and how she dispels gender stereotypes in science by talking to school children as young as five about her career in physics. İşsever also looks forward to the future of particle physics and what could eventually replace the Large Hadron collider as the world’s premier particle-physics experiment.

CERN celebrates 70 years at the helm of particle physics in lavish ceremony

This year marked the 70th anniversary of the world’s most famous physics laboratory, so the last two items in my list celebrate that iconic facility nestled between the Alps and the Jura mountains. Formed in the aftermath of the Second World War, which devastated much of Europe, CERN came into being on 29 September 1954. That year also saw the start of construction of the Geneva-based lab’s proton synchrotron, which fired-up in 1959 with an energy of 24 GeV, becoming the world’s highest-energy particle accelerator. The original CERN had 12 member states and that has since doubled to 24, with an additional 10 associate members. The lab has been associated with a number of Nobel laureates and is a shining example of how science can bring nations together after a the trauma of war. Read more about the anniversary here.

CERN at 70: how the Higgs hunt elevated particle physics to Hollywood status

When former physicist James Gillies sat down for dinner in 2009 with actors Tom Hanks and Ayelet Zurer, joined by legendary director Ron Howard, he could scarcely believe the turn of events. Gillies was the head of communications at CERN, and the Hollywood trio were in town for the launch of Angels & Demons. The  blockbuster film is partly set at CERN with antimatter central to its plot, and is based on the Dan Brown novel. In this Physics World Stories podcast, Gillies looks back on those heady days. Gillies has also written a feature article for us about his Hollywood experience: “Angels & Demons, Tom Hanks and Peter Higgs: how CERN sold its story to the world”.

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With so much fascinating research going on in quantum science and technology, it’s hard to pick just a handful of highlights. Fun, but hard.  Research on entanglement-based imaging and quantum error correction both appear in Physics World’s list of 2024’s top 10 breakthroughs, but beyond that, here are a few other achievements worth remembering as we head into 2025 – the International Year of Quantum Science and Technology.

Quantum sensing

In July, physicists at Germany’s Forschungszentrum Jülich and Korea’s IBS Center for Quantum Nanoscience (QNS) reported that they had fabricated a quantum sensor that can detect the electric and magnetic fields of individual atoms. The sensor consists of a molecule containing an unpaired electron (a molecular spin) that the physicists attached to the tip of a scanning-tunnelling microscope. They then used it to measure the magnetic and electric dipole fields emanating from a single iron atom and a silver dimer on a gold substrate.

Not to be outdone, an international team led by researchers at the University of Melbourne, Australia, announced in August that they had created a quantum sensor that detects magnetic fields in any direction. The new omnidirectional sensor is based on a recently-discovered carbon-based defect in a two-dimensional material, hexagonal boron nitride (hBN). This same material also contains a boron vacancy defect that enables the sensor to detect temperature changes, too.

Quantum communications

One of the challenges with transmitting quantum information is that pretty much any medium you send it through – including high-spec fibre optic cables and even the Earth’s atmosphere  – is at least somewhat good at absorbing photons and preventing them from reaching their intended destination.

In July, a team at the University of Chicago, the California Institute of Technology and Stanford University proposed a novel solution. A continent-scale network of vacuum-sealed tubes, they suggested, could transmit quantum information at rates as high as 10¹³ qubits per second. This would exceed currently-available quantum channels based on satellites or optical fibres by at least four orders of magnitude. Whether anyone will actually build such a network is, of course, yet to be determined – but you have to admire the ambition behind it.

Quantum fundamentals

Speaking of ambition, this year saw a remarkable flurry of ideas for using quantum devices and quantum principles to study gravity. One innovative proposal involves looking for the gravitational equivalent of the photoelectric effect in a system of resonant bars that have been cooled and tuned to vibrate when they absorb a graviton from an incoming gravitational wave. The idea is that absorbing a graviton would change the quantum state of the column, and this change of state would, in principle, be detectable.

Another quantum gravity proposal takes its inspiration from an even older experiment: the Cavendish torsion balance. The quantum version of this 18^th-century classic would involve studying the correlations between two torsion pendula placed close together as they rotate back and forth like massive harmonic oscillators. If correlations appear that can’t be accounted for within a classical theory of gravity, this could imply that gravity is not, in fact, classical.

Perhaps the most exciting development in this space, though, is a new experimental technique for measuring the pull of gravity on a micron-scale particle. Objects of this size are just above the limit where quantum effects start to become apparent, and the Leiden and Southampton University researchers who performed the experiment have ideas for how to push their system further towards this exciting regime. Definitely one to keep an eye on.

The best of the rest

It wouldn’t be quantum if it wasn’t at least little bit weird, so here’s a few head-scratchers for you to puzzle over.

This year, researchers in China substantially reduced the number of qubits required to verify an online shopping transaction. Physicists in Austria asked whether a classical computer can tell when a quantum computer is telling the truth. And in a development that’s sure to warm the hearts of quantum experimentalists the world over, physicists at the SLAC National Laboratory in the US suggested that if your qubits are going haywire and you don’t know why, maybe, just maybe, it’s because they’re being constantly bombarded with dark matter.

Using noisy qubits to detect dark matter? Now that really would be a breakthrough.

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From tumour-killing quantum dots to proton therapy firsts, this year has seen the traditional plethora of exciting advances in physics-based therapeutic and diagnostic imaging techniques, plus all manner of innovative bio-devices and biotechnologies for improving healthcare. Indeed, the Physics World Top 10 Breakthroughs for 2024 included a computational model designed to improve radiotherapy outcomes for patients with lung cancer by modelling the interaction of radiation with lung cells, as well as a method to make the skin of live mice temporarily transparent to enable optical imaging studies. Here are just a few more of the research highlights that caught our eye.

Marvellous MRI machines

This year we reported on some important developments in the field of magnetic resonance imaging (MRI) technology, not least of which was the introduction of a 0.05 T whole-body MRI scanner that can produce diagnostic quality images. The ultralow-field scanner, invented at the University of Hong Kong’s BISP Lab, operates from a standard wall power outlet and does not require shielding cages. The simplified design makes it easier to operate and significantly lower in cost than current clinical MRI systems. As such, the BISP Lab researchers hope that their scanner could help close the global gap in MRI availability.

Moving from ultralow- to ultrahigh-field instrumentation, a team headed up by David Feinberg at UC Berkeley created an ultrahigh-resolution 7 T MRI scanner for imaging the human brain. The system can generate functional brain images with 10 times better spatial resolution than current 7 T scanners, revealing features as small as 0.35 mm, as well as offering higher spatial resolution in diffusion, physiological and structural MR imaging. The researchers plan to use their new NexGen 7 T scanner to study underlying changes in brain circuitry in degenerative diseases, schizophrenia and disorders such as autism.

Meanwhile, researchers at Massachusetts Institute of Technology and Harvard University developed a portable magnetic resonance-based sensor for imaging at the bedside. The low-field single-sided MR sensor is designed for point-of-care evaluation of skeletal muscle tissue, removing the need to transport patients to a centralized MRI facility. The portable sensor, which weighs just 11 kg, uses a permanent magnet array and surface RF coil to provide low operational power and minimal shielding requirements.

Proton therapy progress

Alongside advances in diagnostic imaging, 2024 also saw a couple of firsts in the field of proton therapy. At the start of the year, OncoRay – the National Center for Radiation Research in Oncology in Dresden – launched the world’s first whole-body MRI-guided proton therapy system. The prototype device combines a horizontal proton beamline with a whole-body MRI scanner that rotates around the patient, a geometry that enables treatments both with patients lying down or in an upright position. Ultimately, the system could enable real-time MRI monitoring of patients during cancer treatments and significantly improve the targeting accuracy of proton therapy.

Also aiming to enhance proton therapy outcomes, a team at the PSI Center for Proton Therapy performed the first clinical implementation of an online daily adaptive proton therapy (DAPT) workflow. Online plan adaptation, where the patient remains on the couch throughout the replanning process, could help address uncertainties arising from anatomical changes during treatments. In five adults with tumours in rigid body regions treated using DAPT, the daily adapted plans provided target coverage to within 1.1% of the planned dose and, in over 90% of treatments, improved dose metrics to the targets and/or organs-at-risk. Importantly, the adaptive approach took just a few minutes longer than a non-adaptive treatment, remaining within the 30-min time slot allocated for a proton therapy session.

Bots and dots

Last but certainly not least, this year saw several research teams demonstrate the use of tiny devices for cancer treatment. In a study conducted at the Institute for Bioengineering of Catalonia, for instance, researchers used self-propelling nanoparticles containing radioactive iodine to shrink bladder tumours.

Upon injection into the body, these “nanobots” search for and accumulate inside cancerous tissue, delivering radionuclide therapy directly to the target. Mice receiving a single dose of the nanobots experienced a 90% reduction in the size of bladder tumours compared with untreated animals.

At the Chinese Academy of Sciences’ Hefei Institutes of Physical Science, a team pioneered the use of metal-free graphene quantum dots for chemodynamic therapy. Studies in cancer cells and tumour-bearing mice showed that the quantum dots caused cell death and inhibition of tumour growth, respectively, with no off-target toxicity in the animals.

Finally, scientists at Huazhong University of Science and Technology developed novel magnetic coiling “microfibrebots” and used them to stem arterial bleeding in a rabbit – paving the way for a range of controllable and less invasive treatments for aneurysms and brain tumours.

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December might be dark and chilly here in the northern hemisphere, but it’s summer south of the equator – and for many people that means eating ice cream.

It turns out that the physics of ice cream is rather remarkable – as I discovered when I travelled to Canada’s University of Guelph to interview the food scientist Douglas Goff. He is a leading expert on the science of frozen desserts and in this podcast he talks about the unique material properties of ice cream, the analytical tools he uses to study it, and why ice cream goes off when it is left in the freezer for too long.

 

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Each year, the International Association of Physics Students organizes a physics competition for bachelor’s and master’s students from across the world. Known as the Physics League Across Numerous Countries for Kick-ass Students (PLANCKS), it’s a three-day event where teams of three to four students compete to answer challenging physics questions.

In the UK and Ireland, teams compete in a preliminary competition to be sent to the final. Here are some fiendish questions from past PLANCKS UK and Ireland preliminaries and the 2024 final in Dublin, written by Anthony Quinlan and Sam Carr, for you to try this holiday season.

Question 1: 4D Sun

Imagine you have been transported to another universe with four spatial dimensions. What would the colour of the Sun be in this four-dimensional universe? You may assume that the surface temperature of the Sun is the same as in our universe and is approximately T = 6 × 10³ K. [10 marks]

Boltzmann constant, k_B = 1.38 × 10⁻²³ J K⁻¹

Speed of light, c = 3 × 10⁸ m s⁻¹

Question 2: Heavy stuff

In a parallel universe, two point masses, each of 1 kg, start at rest a distance of 1 m apart. The only force on them is their mutual gravitational attraction, F = –Gm₁m₂/r². If it takes 26 hours and 42 minutes for the two masses to meet in the middle, calculate the value of the gravitational constant G in this universe. [10 marks]

Question 3: Just like clockwork

Consider a pendulum clock that is accurate on the Earth’s surface. Figure 1 shows a simplified view of this mechanism.

A pendulum clock runs on the gravitational potential energy from a hanging mass (1). The other components of the clock mechanism regulate the speed at which the mass falls so that it releases its gravitational potential energy over the course of a day. This is achieved using a swinging pendulum of length l (2), whose period is given by

$T=2\pi \sqrt{\frac{l}{g}}$

where g is the acceleration due to gravity.

Each time the pendulum swings, it rocks a mechanism called an “escapement” (3). When the escapement moves, the gear attached to the mass (4) is released. The mass falls freely until the pendulum swings back and the escapement catches the gear again. The motion of the falling mass transfers energy to the escapement, which gives a “kick” to the pendulum that keeps it moving throughout the day.

Radius of the Earth, R = 6.3781 × 10⁶ m

Period of one Earth day, τ₀ = 8.64 × 10⁴ s

How slow will the clock be over the course of a day if it is lifted to the hundredth floor of a skyscraper? Assume the height of each storey is 3 m. [4 marks]

Question 4: Quantum stick

Imagine an infinitely thin stick of length 1 m and mass 1 kg that is balanced on its end. Classically this is an unstable equilibrium, although the stick will stay there forever if it is perfectly balanced. However, in quantum mechanics there is no such thing as perfectly balanced due to the uncertainty principle – you cannot have the stick perfectly upright and not moving at the same time. One could argue that the quantum mechanical effects of the uncertainty principle on the system are overpowered by others, such as air molecules and photons hitting it or the thermal excitation of the stick. Therefore, to investigate we would need ideal conditions such as a dark vacuum, and cooling to a few milli­kelvins, so the stick is in its ground state.

Moment of inertia for a rod,

$I=\frac{1}{3}m{l}^2$

where m is the mass and l is the length.

Uncertainty principle,

$\Delta x\Delta p\ge \frac{\hslash }{2}$

There are several possible approximations and simplifications you could make in solving this problem, including:

sinθ ≈ θ for small θ

${\cosh }^{-1}x=ln \left(x+\sqrt{x^2-1}\right)$

and

${\sinh }^{-1}x=ln \left(x+\sqrt{x^2+1}\right)$

Calculate the maximum time it would take such a stick to fall over and hit the ground if it is placed in a state compatible with the uncertainty principle. Assume that you are on the Earth’s surface. [10 marks]

Hint: Consider the two possible initial conditions that arise from the uncertainty principle.

• Answers will be posted here on the Physics World website next month. There are no prizes.
• If you’re a student who wants to sign up for the 2025 edition of PLANCKS UK and Ireland, entries are now open at plancks.uk

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A reusable and biodegradable fibrous foam developed by researchers at Wuhan University in China can remove up to 99.8% of microplastics from polluted water. The foam, which is made from a self-assembled network of chitin and cellulose obtained from biomass wastes, has been successfully field-tested in four natural aquatic environments.

The amount of plastic waste in the environment has reached staggering levels and is now estimated at several billion metric tons. This plastic degrades extremely slowly and poses a hazard for ecosystems throughout its lifetime. Aquatic life is particularly vulnerable, as micron-sized plastic particles can combine with other pollutants in water and be ingested by a wide range of organisms. Removing these microplastic particles would help limit the damage, but standard filtration technologies are ineffective as the particles are so small.

A highly porous interconnected structure

The new adsorbent developed by Wuhan’s Hongbing Deng and colleagues consists of intertwined beta-chitin nanofibre sheets (obtained from squid bone) with protonated amines and suspended cellulose fibres (obtained from cotton). This structure contains a number of functional groups, including -OH, -NH₃⁺ and -NHCO- that allow the structure to self-assemble into a highly porous interconnected network.

This self-assembly is important, Deng explains, because it means the foam does not require “complex processing (no cross-linking and minimal use of chemical reagents) or adulteration with toxic or expensive substances,” he tells Physics World.

The functional groups make the surface of the foam rough and positively charged, providing numerous sites that can interact and adsorb plastic particles ranging in size from less than 100 nm to over 1000 microns. Deng explains that multiple mechanisms are at work during this process, including physical interception, electrostatic attraction and intermolecular interactions. The latter group includes interactions that involv hydrogen bonding, van der Waals forces and weak hydrogen bonding interactions (between OH and CH groups, for example).

The researchers tested their foam in lake water, coastal water, still water (a small pond) and water used for agricultural irrigation. They also combined these systematic adsorption experiments with molecular dynamics (MD) simulations and Hirshfeld partition (IGMH) calculations to better understand how the foam was working.

They found that the foam can adsorb a variety of nanoplastics and microplastics, including the polystyrene, polymethyl methacrylate, polypropylene and polyethylene terephthalate found in everyday objects such as electronic components, food packaging and textiles. Importantly, the foam can adsorb these plastics even in water bodies polluted with toxic metals such as lead and chemical dyes. It adsorbed nearly 100% of the particles in its first cycle and around 96-98% of the particles over the following five cycles.

“The great potential of biomass”

Because the raw materials needed to make the foam are readily available, and the fabrication process is straightforward, Deng thinks it could be produced on a large scale. “Other microplastic removal materials made from biomass feedstocks have been reported in recent years, but some of these needed to be functionalized with other chemicals,” he says. “Such treatments can increase costs or hinder their large-scale production.”

 Deng and his team have applied for a patent on the material and are now looking for industrial partners to help them produce it. In the meantime, he hopes the work will help draw attention to the microplastic problem and convince more scientists to work on it. “We believe that the great potential of biomass will be recognized and that the use of biomass resources will become more diverse and thorough,” he says.

The present work is described in Science Advances.

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In my previous article, I highlighted some of the quantum and green-energy companies that won Business Innovation Awards from the Institute of Physics in 2024. But imaging and medical-physics firms did well too. Having sat on the judging panel for the awards, I saw some fantastic entries – and picking winners wasn’t easy. Let me start, though, with Geoptic, which is one of an elite group of firms to win a second IOP business award, adding a Business Innovation Award to its start-up prize in 2020.

Geoptic is a spin-out from three collaborating groups of physicists at the universities of Durham, Sheffield and St Mary’s Twickenham. The company uses cosmic-ray muon radiography and tomography to study large engineering structures. In particular, it was honoured by the IOP for using the technique to ensure the safety of tunnels on the UK’s railway network.

Many of the railway tunnels in the UK date back to the mid-19th century. To speed up construction, temporary shafts were bored vertically down below the ground, allowing workers to dig at multiple points along the route of the tunnel. When the tunnel was complete, the shafts would be sealed, but their precise number and location is often unclear.

The shafts are a major hazard to the tunnel’s integrity, which is not great for Network Rail – the state-owned body that’s responsible for the UK’s rail infrastructure. Geoptic has, however, been working with Network Rail to provide its engineers with a clear structural view of the dangers that lurk along its route. In my view, it’s a really innovating imaging company, solving challenging real-world problems.

Another winner is Silveray, which was spun off from the University of Surrey. It’s picked up an IOP Business Start-up Award for creating flexible, “colour” X-ray detectors based on proprietary semiconductor materials. Traditional X-ray images are black and white, but what Silveray has done is to develop a nano-particle semiconductor ink that can be coated on to any surface and work at multiple wavelengths.

The X-ray detectors, which are flexible, can simply be wrapped around pipes and other structures that need to be imaged. Traditionally, this has been done using analogue X-ray film that has to be developed in an off-site dark room. That’s costly and time-consuming – especially if images failed to be recorded. Silveray’s detectors instead provide digital X-ray images in real time, making it an exciting and innovative technology that could transform the $5bn X-ray detector market.

Phlux Technology, meanwhile, has won an IOP Business Start-up Award for developing patented semiconductor technology for infrared light sensors that are 12 times more sensitive than the best existing devices, making them ideal for fast, accurate 3D imaging. Set up by researchers at the University of Sheffield, Phlux’s devices have many potential applications especially in light detection and ranging (LIDAR), laser range finders, optical-fibre test instruments and optical and quantum communications networks.

In LIDAR, Phlux’s can have 12 times greater image resolution for a given transmitter power. Its sensors could also make vehicles much safer by enabling higher-resolution images to be created over longer distances, making safety systems more effective. The first volume market for the company is likely to be in communications and where a >10 dB increase in detector sensitivity is going to be well received by the market.

Given the number of markets that will benefit from an “over an order of magnitude” improvement, Phlux is one to watch for a future Business Innovation Award too.

Medical marvel

Let me finish by mentioning Crainio, a medical technology spin-off company from City, University of London, which has won the 2024 Lee Lucas award. This award honours promising start-up firms in the medical and healthcare sector thanks to a generous donation by Mike and Ann Lee (née Lucas). These companies need all the support, time and money they can get given the many challenging regulatory requirements in the medical sector.

Crainio’s technology allows healthcare workers to measure intracranial pressure (ICP), a vital indicator of brain health after a head injury. Currently, the only way to measure ICP directly is for a neurosurgeon to drill a hole in a patient’s skull and place an expensive probe in the brain. It’s a highly invasive procedure that can’t easily be carried out in the “golden hours” immediately after an accident, requiring access to scarce and expensive neurosurgery resources. The procedure is also medically risky, leading to potential infection, bleeding and other complications.

Crainio’s technology eliminates these risks, enabling direct measurement of ICP through a simple non-invasive probe applied to the forehead. The technology – using infrared photoplethysmography (PPG) combined with machine learning – is based on years of research and development work conducted by Panicos Kyriacou and his team of biomedical engineers at City.

Good levels of accuracy have been demonstrated in clinical studies conducted at the Royal London Hospital. It certainly seems a much better plan than drilling a hole in your head as I am sure you can agree – making Crainio a worthy winner, with its non-invasive technology it should have a positive impact on patients globally. I hope the regulatory hurdles can be quickly cleared so the company can start helping patients as soon as possible.

As I have mentioned before, all physics-based firms require time and energy to develop products and become globally significant. There’s also the perennial difficulty of explaining a product idea, which is often quite specialized, to potential investors who have little or no science background. An IOP start-up award can therefore show that your technology has won approval from judges with solid physics and business experience.

I hope, therefore, that your company, if you have one, will be inspired to apply. Also remember that the IOP offers three other awards (Katharine Burr Blodgett, Denis Gabor and Clifford Paterson) for individuals or teams who have been involved in innovative physics with a commercial angle. Good luck – and remember, you have to be in it to win it. Award entries for 2025 will be open in February 2025.

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What skills do you use every day in your job?

Right now, I spend 95% of my time being a dean, and in that job the skill I use every day is problem-solving. That’s one of the first things we learn as physicists: it’s not enough just to know the technical background, you have to be able to apply it. I find myself looking at everything as systems of equations – this person wants this, this thing needs to go there, we need money to do that thing – and thinking about how to put them together. We do a really good job in physics of teaching people how to think, so they can take a broad look at things and make them work.

What do you like best and least about your job?

The thing I like best is the opportunity to have a wide impact, not just on the faculty who are doing amazing research, but also on students – our next generation of scientific leaders – and people in the wider community. We do a lot of public service outreach at UChicago PME. Outreach has had a big impact on me so it’s incredibly satisfying that, as dean, I can provide those opportunities at various levels for others.

The thing I like least is that because we have so much to do, figuring out who can do what, and how – within what are always limited resources – often feels like trying to solve a giant jigsaw puzzle. Half the time, it feels like the puzzle board is bigger than the number of pieces, so I’m figuring out how to make things work in ways that sometimes stretch people thin, which can be very frustrating for everybody. We all want to do the best job we can, but we need to understand that we sometimes have limits.

What do you know today that you wish you’d known at the start of your career?

I feel a little guilty saying this because I’m going to label myself as a true “in the lab” scientist, but I wish I’d known how much relationships matter. Early on, when I was a junior faculty member, I was focused on research; focused on training my students; focused on just getting the work done. But it didn’t take long for me to realize that of course, students aren’t just workers. They are twenty-somethings with lives and aspirations and goals.

Thankfully, I figured that out pretty quickly, but at every step along the way, as I try to focus on the problem to solve, I have to remind myself that people aren’t problems. People are people, and you have to work with them to solve problems in ways that work for everybody. I sometimes wish there was more personnel training for faculty, rather than a narrow focus on papers and products, because it really is about people at the end of the day.

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Transcranial focused ultrasound is being developed as a potential treatment for various brain diseases and disorders. One big challenge, however, is focusing the ultrasound through the skull, which can blur, attenuate and shift the beam. To minimize these effects, researchers at Zeta Surgical have developed an algorithm that automatically determines the optimal location to place a single-element focused transducer.

For therapeutic applications – including, for example, thermal ablation, drug delivery, disruption of the blood–brain barrier and neuromodulation – the ultrasound beam must be focused onto a small spot in the brain. The resulting high acoustic pressure at this spot generates a high temperature or mechanical force to treat the targeted tissues, ideally while avoiding overheating of nearby healthy tissues.

Unfortunately, when the ultrasound beam passes through the skull, which is a complex layered structure, it is both attenuated and distorted. This decreases the acoustic pressure at the focus, defocusing the beam and shifting the focus position.

Ultrasound arrays with multiple elements can compensate for such aberrations by controlling the individual array elements. But cost constraints mean that most applications still use single-element focused transducers, for which such compensation is difficult. This can result in ineffective or even unsafe treatments. What’s needed is a method that finds the optimal position to place a single-element focused ultrasound transducer such that defocusing and focus shift are minimized.

Raahil Sha and colleagues have come up with a way to do just this, using an optimization algorithm that simulates the ultrasound field through the skull. Using the k-Wave MATLAB toolbox, the algorithm simulates ultrasound fields generated within the skull cavity with the transducer placed at different locations. It then analyses the calculated fields to quantify the defocusing and focus shift.

The algorithm starts by loading a patient CT scan, which provides information on the density, speed of sound, absorption, geometry and porosity of the skull. It then defines the centre point of the target as the origin and the centre of a single-element 0.5 MHz transducer as the initial transducer location, and determines the initial values of the normalized peak-negative pressure (PNP) and focal volume.

The algorithm then performs a series of rotations of the transducer centre, simulating the PNP and focal volume at each new location. The PNP value is used to quantify the focus shift, with a higher PNP at the focal point representing a smaller shift.

Any change in the focal position is particularly concerning as it can lead to off-target tissue disruption. As such, the algorithm first identifies transducer positions that keep the focus shift below a specified threshold. Within these confines, it then finds the location with the smallest focal volume. This is then output as the optimal location for placing the transducer. In this study, this optimal location had a normalized PNP of 0.966 (higher than the pre-set threshold of 0.95) and a focal volume 6.8% smaller than that without the skull in place.

Next, the team used a Zeta neuro-navigation system and a robotic arm to automatically guide a transducer to the optimal location on a head phantom and track the placement accuracy in real time. In 45 independent registration attempts, the surgical robot could position the transducer at the optimal location with a mean position error of 0.0925 mm and a mean trajectory angle error of 0.0650 mm. These low values indicate the potential for accurate transducer placement during treatment.

The researchers conclude that the algorithm can find the optimal transducer location to avoid large focus shift and defocusing. “With the Zeta navigation system, our algorithm can help to make transcranial focused ultrasound treatment safer and more successful,” they write.

The study is reported in Bioengineering.

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The Physics World 2024 Breakthrough of the Year goes to Mikhail Lukin, Dolev Bluvstein and colleagues at Harvard University, the Massachusetts Institute of Technology and QuEra Computing, and independently to Hartmut Neven and colleagues at Google Quantum AI and their collaborators, for demonstrating quantum error correction on an atomic processor with 48 logical qubits, and for implementing quantum error correction below the surface code threshold in a superconducting chip, respectively.

Errors caused by interactions with the environment – noise – are the Achilles heel of every quantum computer, and correcting them has been called a “defining challenge” for the technology. These two teams, working with very different quantum systems, took significant steps towards overcoming this challenge. In doing so, they made it far more likely that quantum computers will become practical problem-solving machines, not just noisy, intermediate-scale tools for scientific research.

Quantum error correction works by distributing one quantum bit of information – called a logical qubit – across several different physical qubits such as superconducting circuits or trapped atoms. While each physical qubit is noisy, they work together to preserve the quantum state of the logical qubit – at least for long enough to do a computation.

Formidable task

Error correction should become more effective as the number of physical qubits in a logical qubit increases. However, integrating large numbers of physical qubits to create a processor with multiple logical qubits is a formidable task. Furthermore, adding more physical qubits to a logical qubit also adds more noise – and it is not clear whether making logical qubits bigger would make them significantly better. This year’s winners of our Breakthrough of the Year have made significant progress in addressing these issues.

The team led by Lukin and Bluvstein created a quantum processor with 48 logical qubits that can execute algorithms while correcting errors in real time. At the heart of their processor are arrays of neutral atoms. These are grids of ultracold rubidium atoms trapped by optical tweezers. These atoms can be put into highly excited Rydberg states, which enables the atoms to act as physical qubits that can exchange quantum information.

What is more, the atoms can be moved about within an array to entangle them with other atoms. According to Bluvstein, moving groups of atoms around the processor was critical for their success at addressing a major challenge in using logical qubits: how to get logical qubits to interact with each other to perform quantum operations. He describes the system as a “living organism that changes during a computation”.

Their processor used about 300 physical qubits to create up to 48 logical qubits, which were used to perform logical operations. In contrast, similar attempts using superconducting or trapped-ion qubits have only managed to perform logical operations using 1–3 logical qubits.

Willow quantum processor

Meanwhile, the team led by Hartmut Neven made a significant advance in how physical qubits can be combined to create a logical qubit. Using Google’s new Willow quantum processor – which offers up to 105 superconducting physical qubits – they showed that the noise in their logical qubit remained below a maximum threshold as they increased the number of qubits.  This means that the logical error rate is suppressed exponentially as the number of physical qubits per logical qubit is increased.

Neven told Physics World that the Google system is “the most convincing prototype of a logical qubit built today”. He said that that Google is on track to develop a quantum processor with 100 or even 1000 logical qubits by 2030. He says that a 1000 logical qubit device could do useful calculations for the development of new drugs or new materials for batteries.

Bluvstein, Lukin and colleagues are already exploring how their processor could be used to study an effect called quantum scrambling. This could shed light on properties of black holes and even provide important clues about the nature of quantum gravity.

You can listen to Neven talk about his team’s research in this podcast. Bluvstein and Lukin talk about their group’s work in this podcast.

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 2024, 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 2024, which served as our shortlist. The other nine breakthroughs are listed below in no particular order.

Light-absorbing dye turns skin of live mouse transparent

To a team of researchers at Stanford University in the US for developing a method to make the skin of live mice temporarily transparent. One of the challenges of imaging biological tissue using optical techniques is that tissue scatters light, which makes it opaque. The team, led by Zihao Ou (now at The University of Texas at Dallas), Mark Brongersma and Guosong Hong, found that the common yellow food dye tartrazine strongly absorbs near-ultraviolet and blue light and can help make biological tissue transparent. Applying the dye onto the abdomen, scalp and hindlimbs of live mice enabled the researchers to see internal organs, such as the liver, small intestine and bladder, through the skin without requiring any surgery. They could also visualize blood flow in the rodents’ brains and the fine structure of muscle sarcomere fibres in their hind limbs. The effect can be reversed by simply rinsing off the dye. This “optical clearing” technique has so far only been conducted on animals. But if extended to humans, it could help make some types of invasive biopsies a thing of the past.

Laser cooling positronium 

To the AEgIS collaboration at CERN, and Kosuke Yoshioka and colleagues at the University of Tokyo, for independently demonstrating laser cooling of positronium. Positronium, an atom-like bound state of an electron and a positron, is created in the lab to allow physicists to study antimatter. Currently, it is created in “warm” clouds in which the atoms have a large distribution of velocities, making precision spectroscopy difficult. Cooling positronium to low temperatures could open up novel ways to study the properties of antimatter. It also enables researchers to produce one to two orders of magnitude more antihydrogen – an antiatom comprising a positron and an antiproton that’s of great interest to physicists. The research also paves the way to use positronium to test current aspects of the Standard Model of particle physics, such as quantum electrodynamics, which predicts specific spectral lines, and to probe the effects of gravity on antimatter.

Modelling lung cells to personalize radiotherapy

To Roman Bauer at the University of Surrey, UK, Marco Durante from the GSI Helmholtz Centre for Heavy Ion Research, Germany, and Nicolò Cogno from GSI and Massachusetts General Hospital/Harvard Medical School, US, for creating a computational model that could improve radiotherapy outcomes for patients with lung cancer. Radiotherapy is an effective treatment for lung cancer but can harm healthy tissue. To minimize radiation damage and help personalize treatment, the team combined a model of lung tissue with a Monte Carlo simulator to simulate irradiation of alveoli (the tiny air sacs within the lungs) at microscopic and nanoscopic scales. Based on the radiation dose delivered to each cell and its distribution, the model predicts whether each cell will live or die, and determines the severity of radiation damage hours, days, months or even years after treatment. Importantly, the researchers found that their model delivered results that matched experimental observations from various labs and hospitals, suggesting that it could, in principle, be used within a clinical setting.

A semiconductor and a novel switch made from graphene

To Walter de Heer, Lei Ma and colleagues at Tianjin University and the Georgia Institute of Technology, and independently to Marcelo Lozada-Hidalgo of the University of Manchester and a multinational team of colleagues, for creating a functional semiconductor made from graphene, and for using graphene to make a switch that supports both memory and logic functions, respectively. The Manchester-led team’s achievement was to harness graphene’s ability to conduct both protons and electrons in a device that performs logic operations with a proton current while simultaneously encoding a bit of memory with an electron current. These functions are normally performed by separate circuit elements, which increases data transfer times and power consumption. Conversely, de Heer, Ma and colleagues engineered a form of graphene that does not conduct as easily. Their new “epigraphene” has a bandgap that, like silicon, could allow it to be made into a transistor, but with favourable properties that silicon lacks, such as high thermal conductivity.

Detecting the decay of individual nuclei

To David Moore, Jiaxiang Wang and colleagues at Yale University, US, for detecting the nuclear decay of individual helium nuclei by embedding radioactive lead-212 atoms in a micron-sized silica sphere and measuring the sphere’s recoil as nuclei escape from it. Their technique relies on the conservation of momentum, and it can gauge forces as small as 10^-20 N and accelerations as tiny as 10^-7 g, where g is the local acceleration due to the Earth’s gravitational pull. The researchers hope that a similar technique may one day be used to detect neutrinos, which are much less massive than helium nuclei but are likewise emitted as decay products in certain nuclear reactions.

Two distinct descriptions of nuclei unified for the first time

To Andrew Denniston at the Massachusetts Institute of Technology in the US, Tomáš Ježo at Germany’s University of Münster and an international team for being the first to unify two distinct descriptions of atomic nuclei. They have combined the particle physics perspective – where nuclei comprise quarks and gluons – with the traditional nuclear physics view that treats nuclei as collections of interacting nucleons (protons and neutrons). The team has provided fresh insights into short-range correlated nucleon pairs – which are fleeting interactions where two nucleons come exceptionally close and engage in strong interactions for mere femtoseconds. The model was tested and refined using experimental data from scattering experiments involving 19 different nuclei with very different masses (from helium-3 to lead-208). The work represents a major step forward in our understanding of nuclear structure and strong interactions. 

New titanium:sapphire laser is tiny, low-cost and tuneable

To Jelena Vučković, Joshua Yang, Kasper Van Gasse, Daniil Lukin, and colleagues at Stanford University in the US for developing a compact, integrated titanium:sapphire laser that needs only a simple green LED as a pump source. They have reduced the cost and footprint of a titanium:sapphire laser by three orders of magnitude and the power consumption by two. Traditional titanium:sapphire lasers have to be pumped with high-powered lasers – and therefore cost in excess of $100,000. In contrast, the team was able to pump its device using a $37 green laser diode. The researchers also achieved two things that had not been possible before with a titanium:sapphire laser. They were able to adjust the wavelength of the laser light and they were able to create a titanium:sapphire laser amplifier. Their device represents a key step towards the democratization of a laser type that plays important roles in scientific research and industry.

Entangled photons conceal and enhance images

To two related teams for their clever use of entangled photons in imaging. Both groups include Chloé Vernière and Hugo Defienne of Sorbonne University in France, who as duo used quantum entanglement to encode an image into a beam of light. The impressive thing is that the image is only visible to an observer using a single-photon sensitive camera – otherwise the image is hidden from view. The technique could be used to create optical systems with reduced sensitivity to scattering. This could be useful for imaging biological tissues and long-range optical communications. In separate work, Vernière and Defienne teamed up with Patrick Cameron at the UK’s University of Glasgow and others to use entangled photons to enhance adaptive optical imaging. The team showed that the technique can be used to produce higher-resolution images than conventional bright-field microscopy. Looking to the future, this adaptive optics technique could play a major role in the development of quantum microscopes.

First samples returned from the Moon’s far side

To the China National Space Administration for the first-ever retrieval of material from the Moon’s far side, confirming China as one of the world’s leading space nations. Landing on the lunar far side – which always faces away from Earth – is difficult due to its distance and terrain of giant craters with few flat surfaces. At the same time, scientists are interested in the unexplored far side and why it looks so different from the near side. The Chang’e-6 mission was launched on 3 May consisting of four parts: an ascender, lander, returner and orbiter. The ascender and lander successfully touched down on 1 June in the Apollo basin, which lies in the north-eastern side of the South Pole-Aitken Basin. The lander used its robotic scoop and drill to obtain about 1.9 kg of materials within 48 h. The ascender then lifted off from the top of the lander and docked with the returner-orbiter before the returner headed back to Earth, landing in Inner Mongolia on 25 June. In November, scientists released the first results from the mission finding that fragments of basalt – a type of volcanic rock – date back to 2.8 billion years ago, indicating that the lunar far side was volcanically active at that time. Further scientific discoveries can be expected in the coming months and years ahead as scientists analyze more fragments.

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One half of the Physics World 2024 Breakthrough of the Year has been awarded to Mikhail Lukin, Dolev Bluvstein and colleagues at Harvard University, the Massachusetts Institute of Technology and QuEra Computing for demonstrating quantum error correction on an atomic processor with 48 logical qubits.

In this episode of the Physics World Weekly podcast, Bluvstein and Lukin explain the crucial role that error correction is playing in the development of practical quantum computers. They also describe how atoms are moved around their quantum processor and why this coordinated motion allowed them to create logical qubits and use those qubits to perform quantum computations.

The Physics World 2024 Breakthrough of the Year also cites Hartmut Neven and colleagues at Google Quantum AI and their collaborators for implementing quantum error correction below the surface code threshold in a superconducting chip. Neven talks about his team’s accomplishments in this podcast.

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One half of the Physics World 2024 Breakthrough of the Year has been awarded to Hartmut Neven and colleagues at Google Quantum AI and their collaborators for implementing quantum error correction below the surface code threshold in a superconducting chip.

In this episode of the Physics World Weekly podcast, Neven talks about Google’s new Willow quantum processor, which integrates 105 superconducting physical qubits. He also explains how his team used these qubits to create logical qubits with error rates that dropped exponentially with the number of physical qubits used. He also outlines Googles ambitious plan to create a processor with 100, or even 1000, logical qubits by 2030.

The Physics World 2024 Breakthrough of the Year also cites Mikhail Lukin, Dolev Bluvstein and colleagues at Harvard University, the Massachusetts Institute of Technology and QuEra Computing for demonstrating quantum error correction on an atomic processor with 48 logical qubits. Lukin and Bluvstein explain how they did it in this podcast.

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A building may be little more than bricks and mortar, but behind the façade it can bring people together and catalyse change. That was the vision for the main facility of the UK’s National Quantum Computing Centre (NQCC), located on the Harwell Campus in Oxfordshire, which is designed to foster collaboration and accelerate innovation across all parts of the UK’s quantum ecosystem.

At the official opening of the building, held at the end of October 2024, the NQCC team showed how that original vision had been turned into reality. In the new experimental labs on the ground floor, NQCC scientists who were previously working as individual teams in borrowed facilities around the Harwell site are now working in an environment where they can swap notes with colleagues working on other hardware platforms.

“It is always useful to have other scientists around to share ideas and solve specific problems,” said Klara Theophilo, an atomic physicist who is setting up trapped-ion systems based on chips originally developed at the University of Oxford and the National Physical Laboratory (NPL). “Trapped-ion systems share some of the same challenges as hardware platforms based on neutral atoms, while the cryogenic engineering we need is also being used for systems based on superconducting qubits.”

Theophilo and her scientific colleagues are benefiting from state-of-the-art experimental facilities purpose-designed for building and testing quantum computers. “This lab has the best environmental control I have ever worked in,” she said. “To achieve high gate fidelities we need careful control of both the temperature and the humidity to ensure that our lasers can manipulate the qubits with high precision, and in our previous lab space there was a constant need to realign and recalibrate the lasers.”

Joining the NQCC technical teams will be scientists and engineers from commercial companies who are building their own systems for quantum computing. In the coming months, several firms are due to install prototype hardware platforms commissioned by the NQCC as part of its programme to establish seven experimental testbeds based on different qubit modalities.

Others will be hosted at the Innovation Hub, the NQCC’s other facility on the Harwell Campus, while quantum networking company NuQuantum is also preparing to establish a team within the main building for a three-year co-development project with the NQCC. The aim of this programme, called Project IDRA, will be to build a distributed quantum computing system that will connect together multiple hardware nodes by entangling the qubits in different quantum processors.

 facility like the NQCC can act like an anchor for businesses to build around, creating a cluster of companies that form a supply chain for each other

Mark Thomson, executive chair of the Science and Technology Facilities Council (STFC)

For the NQCC and its backers, the longer term hope is that bringing these hardware companies into the national lab will catalyse the formation of a quantum cluster in and around the Harwell Campus.

“We have a unique ability on this site to connect academia and national infrastructure with start-up businesses and large enterprise,” said Mark Thomson, currently the executive chair of the Science and Technology Facilities Council (STFC) and soon to be the new director general of CERN. “A facility like the NQCC can act like an anchor for businesses to build around, creating a cluster of companies that form a supply chain for each other. We have already seen that in the space sector, and I genuinely believe that we will now see the same clustering effect for quantum technologies.”

Indeed, many of the hardware providers who are installing their prototype systems within the NQCC are eager to find new ways to work with the national lab and its growing network of academic and commercial partners. “Establishing a presence in the NQCC is a great way for us to become more connected with the UK’s wider quantum ecosystem,” said Alice Voaden, project manager for Rigetti, one of the testbed providers. “It puts us in a better position to identify future opportunities for collaboration, which could help us to explore how emerging applications and software strategies can work with our technology.”

Beyond the technical work, the new facility brings together the NQCC’s growing team of technical and innovation specialists under the same roof for the first time. Previously distributed among temporary office spaces across the Harwell Campus, around 80 people working across a diverse range of activities now have the chance to make new connections and forge a collective identity that will help to establish the NQCC as a focal point for quantum computing in the UK and beyond.

Indeed, since the NQCC was established in 2020 it has put an increasing emphasis on building a community of hardware providers, software developers and end users who can work together to explore the value of quantum computing for the benefit of society and the economy.

“The early vision for the NQCC was to address the issue of scaling in quantum computing, and originally we were primarily focused on technology development,” commented NQCC director Michael Cuthbert. “But increasingly we’ve been turning our attention to scaling the user community for quantum computing, and today is an opportunity for us to highlight our activities across the breadth of our programme.”

Those efforts include providing easy access to quantum computing resources, offering learning opportunities to boost the ranks of scientists and engineers with an understanding of quantum computers, and working directly with organizations in the public and private sectors to develop use cases where quantum computing can make a meaningful impact.

In one example highlighted at the inauguration, applications engineers from the NQCC are working with software company Unisys and the University of Newcastle to explore how today’s quantum computers could be used to optimize the loading of cargo onto aircraft, which can cut fuel costs and reduce carbon emissions.

“What happens here will create jobs and businesses, and it will benefit people across the UK and beyond,” said Science Minister Lord Patrick Vallance, who officially opened the building. “You have created something that will bring academics and people from industry together to harness the power of quantum computing to solve problems that really matter.”

Another element of the NQCC’s remit is to provide clear, trusted and impartial guidance to government, businesses and the  ublic. It is already working with NPL and other government and industry bodies on standards development, with the NQCC spearheading the global debate around responsible and ethical quantum computing. “Gaining public trust is vital to drive user adoption,” said Cuthbert. “The NQCC is in a unique position to provide thought leadership on ethical considerations, which will ultimately benefit the whole community.”

While the inauguration of the UK’s newest national lab was focused on the prospects for quantum computing, there were also reminders that the NQCC is a direct result of the country’s established strength in quantum science and technology. Following decades of basic research across many contributing disciplines, the National Quantum Technologies Programme, which has seen more than £1bn of investment since 2014, has been created a collaborative culture in which academics work in tandem with start-up companies to translate scientific insights into innovative technologies.

“We know that quantum computing will be a long-haul journey that requires some patience, but the NQCC is already showing what can be achieved through collaboration and co-location,” said Peter Knight, the architect of the NQTP and the instigator behind the NQCC. “Bringing companies and academics into the facility will enable dialogue, drive future collaboration, and accelerate progress towards our mission of delivering quantum computing at scale.”

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Microscopic robots with small-scale features that can control light at the microscale offer the potential to probe the microscopic world in more detail – with the scattering of light from such microbots able to induce diffractive optical effects.

To date, this combination of diffractive optics and tuneable mechanics has primarily exploited microelectromechanical systems (MEMS) devices, but creating actuatable microbots with features on the scale of the wavelength of light has been challenging.

To address this challenge, researchers at Cornell University turned to magnetically controlled microbots. While such robots have been developed at millimetre scales, the ability to perform magnetic actuation at the micron scale only became possible recently, due to the creation of protocols that encode magnetic information into microscale robotics and the use of atomic layer deposition (ALD) to create nanoscale hinges that make flexible micromachines capable of advanced navigation.

The team has now created magnetically controlled microbots that operate at the visible-light diffraction limit, so-called diffractive robots.

“A walking robot that’s small enough to interact with and shape light effectively takes a microscope’s lens and puts it directly into the microworld,” says team leader Paul McEuen in a press statement. “It can perform up-close imaging in ways that a regular microscope never could.”

New magnetic microbots

Using nanometre-scale mechanical membranes, rigid panels, programmable nanomagnets and diffractive optical elements, McEuen and colleagues created untethered microbots that are small enough to diffract visible light. They used the ALD hinges to connect the microbot’s rigid panels with magnetically actuatable joints, enabling them to reconfigure and move in millitesla-scale magnetic fields.

The core elements of the diffractive microbots comprise the light-diffracting panels with integrated nanomagnet arrays and the flexible hinges; the platform can also embed optical elements such as an optical diffraction grating. To enable the required mechanical, diffractive and magnetic performance, these integrated elements span several orders of magnitude in terms of their individual scales. The light diffracting grating panels were tens of microns in size, with each panel 1 µm wide, whereas the diffractive grating lines were on the scale of light wavelengths, the hinges had a thickness of 5 nm, and the magnetic domains were in the nanoscale realm.

The hinges played a crucial role, the researchers note, by providing a high degree of flexibility to an otherwise rigid robot. This flexibility allowed the microbots to rotate and reorientate themselves to dynamically change how light is diffracted, focused and redirected.

When manipulated with a magnetic field, the microrobots were able to simultaneously change shape, locomote along a surface and control diffracted light. This locomotion capability was due to the array of nanomagnets integrated into the light-diffracting grating panels.

By selectively controlling the aspect ratio of the nanomagnet domains and programming them using the strength of the external magnetic field, the researchers could control the movement of the microbots – including crawling forward on a solid surface and “swimming” through fluids while simultaneously steering and diffracting light.

“These robots are 5 microns to 2 microns,” says co-author Itai Cohen. “They’re tiny. And we can get them to do whatever we want by controlling the magnetic fields driving their motions.”

The researchers note that the tuneability of the optical elements could be further improved by adding more magnetic material to the microbots and/or increasing the size of the magnetic fields used to control them. And while this study centred around individual microbots, it should also be possible to use multiple microbots in magnetically actuated robot swarms to introduce collective optical effects.

Potential applications

As a generalized robotics platform, the microbots could easily be modified and produced with differing sizes, geometries and optical elements according to the intended application. Some key optical elements that could be integrated include meta-atoms, subwavelength apertures and plasmonic resonant probes.

The researchers have already demonstrated that the microbots have capabilities including force sensing with piconewton sensitivity, subdiffractive imaging using a type of structured illumination microscopy, and light beam steering and focusing using tunable diffractive optical elements. Other potential applications include endoscopic imaging and tissue ablation, high-resolution fluorescence microscopy of cells, and the high-resolution sensing of magnetic fields and current in integrated circuits.

The research is described in Science.

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Physics takes us from the far reaches of the universe to the subatomic scale. A passion for physics also takes us further than we imagined possible, building skills that set us up for life, no matter what path we follow in our careers.

If you’re a physicist or physics professional, your drive for the subject is invaluable. By sharing your passion, you show others how far physics could take them. It can be intimidating, but outreach is vital for nurturing the next generation of physicists, promoting public understanding of science and building a skilled physics community.

Outreach is also an important part of the mission of The Ogden Trust – a UK-based charitable organization that promotes the teaching and learning of physics. The trust has been supporting university physics outreach since 2005, with nearly all universities in England that offer physics undergraduate degrees – and several in Scotland and Wales too – having worked with the trust.

As well as providing funding for public engagement and outreach initiatives, the trust also supports universities through the Outreach Officer Network and annual Outreach Awards. So as a physicist, how can you get involved in outreach? Here are some tips and case studies to inspire you along your journey.

Starting out strong

Just as collaboration and shared tools are vital for physics research, there is also a wealth of support that physicists interested in outreach can draw on. No matter how ambitious your idea is, remember that others have been in your position before. Accessing shared resources and training will make starting out much easier (see box on the Physics Mentoring Project).

You could begin by signing up for The Interact Symposium, a biennial event for physical scientists seeking to gain new skills and share their experiences of public engagement. Run by the Science and Technology Facilities Council (STFC), the Institute of Physics (IOP), The Ogden Trust, the Royal Astronomical Society and the South East Physics Network (SEPnet), a bank of resources from the 2024 symposium is available online, including lots of examples of successful projects.

Meanwhile, many departments in universities, schools and workplaces have a specialist outreach co-ordinator whose experience you could tap into. If there isn’t, you might have a more experienced colleague who can advise you and share community or school links. You could also contact your local IOP branch committee or join the IOP’s Physics Communicators Group.

As with any scientific endeavour, it’s important to do your research. Attending local science festivals and community events will give you great ideas and inspiration. One day, they may even provide an opportunity to deliver your own outreach.

Strategic thinking

So, you’ve tried outreach for the first time and are eager to do more. It’s tempting to jump straight in. But before making any big commitments, it is worth making a long-term strategic plan.

Your department might have an engagement-specific strategy or other priorities that could be linked to your activities. If there is a dedicated outreach or public engagement professional in your organization, they can advise on this. If your workplace doesn’t have a strategy for outreach and engagement, you could advocate for one to be written (see box on the Institute of Cosmology and Gravitation, University of Portsmouth, UK).

In the UK, the quality of research in higher-education institutions is assessed by the Research Excellence Framework (REF), the results of which informs research funding allocations. Part of the exercise considers the impact of research on people, culture and environment. In REF 2021 around half the impact case studies submitted featured outreach and engagement activities.

In 2021 The Ogden Trust released the Taking a Strategic Approach to Outreach guide. In partnership with the STFC, the trust also funds an annual leadership training course for outreach and public engagement which equips academics and teaching staff with the skills to plan and deliver effective outreach.

At this point, you should also consider whether you have all the resources you need. It is often possible to deliver activities with equipment from your institution but, as you do more, the cost of travel, time and equipment can add up. You may be able to fund activities from your existing budgets, particularly if they are closely related to your work. However, you may also need to consider external funding opportunities.

Engagement funding is available through a number of organizations. For example, the STFC has created the Spark awards (£1000–15,000), Nucleus awards (£15,000–125,000) and other grants to engage the public with STFC science. The IOP public-engagement grant scheme awards £500-4000 to improve young people’s relationship with physics. The Royal Academy of Engineering, meanwhile, has its Ingenious grant scheme, which offers funding of £3000–30,000 for projects that engage under-represented audiences.

Remember that while one-off outreach activities can spark your audience’s interest, building long-term partnerships is often more effective. Outreach work with schools is ideally suited for this kind of approach – in fact, regular interactions with a school can tackle systemic inequalities in UK STEM education (see box on Orbyts).

You should also think about your target audience. A lot of physics engagement takes place in schools but partnerships with community organizations can reach those who may not attend science festivals or talks. There may be an increased willingness to engage in physics outside of the classroom, where it can capture the imagination of young people who find a school environment challenging (see box on My Place, My Science).

Steps to success

As with any activity in which you are investing your time and energy, it is important to know whether you are achieving your outreach goals. Having a clear strategy will give you a clear idea of what success looks like, but effective evaluation should also be built into your project from the start.

This will also be valuable if you have to justify the time and money spent on a project or make funding applications. The STFC has a useful public engagement evaluation framework that you can follow. The Ogden Trust has also published an evaluation toolkit for working with young people that uses the science capital framework.

Bear in mind that evaluation doesn’t always mean surveys and quantitative data. You might instead get verbal feedback from participants or ask someone else to observe you. In a university, you could consult colleagues in education or social-science departments who are familiar with such methodologies. For larger projects or those for REF or business cases, you could turn to an external evaluator to  provide an independent perspective.

Physicists know that their subject impacts everything from space exploration to sustainable technology, but unfortunately many people don’t think physics is for them. Young people from disadvantaged backgrounds, in particular, struggle to see themselves as future physicists. Outreach can make a real difference by showing that you don’t need to belong to a specific group or demographic to be a physicist – all you need is a passion for the subject.

• For more information about The Ogden Trust or to sign up for its Physics Outreach Network newsletter, visit its website or e-mail outreach@ogdentrust.com.

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When surgery is performed to remove cancerous tissue, one question always lingers: “did the surgeon get everything?”.

In the case of brain tumour resection, the answer is often “no”. Residual cancerous tissue at the edges of a cavity where a malignant mass has been removed can visually resemble healthy tissue and be overlooked, or may be microscopic in size.

A new tool for neurosurgeons, designed for fast and accurate detection of microscopic brain tumour infiltration in unprocessed tissue samples from surgical margins, may lead to a new era of success for brain cancer surgery.

The developers of the new FastGlioma tool, at the University of Michigan and the University of California, San Francisco (UCSF), explain that it can predict if and the extent to which glioma remains in the brain while the surgical procedure is underway. FastGlioma also provides visual heat-map guidance of the location(s) requiring additional reaction for safe maximal tumour removal.

FastGlioma combines rapid, easy-to-use stimulated Raman histology (SRH) optical imaging with open-source visual foundation models (artificial intelligence models trained on massive, diverse datasets that can be adapted for a wide range of tasks) to perform a 10 s analysis of fresh tissue specimens in operating room suites. FastGlioma proved not only significantly faster and cheaper than conventional standard-of-care MRI- and fluorescence-based surgical guidance, but in head-to-head comparisons, it significantly outperformed them in detection of two types of glioma (IDH wild-type and IDH-mutant diffuse gliomas).

Training and validation

In a prospective multicentre clinical study, principal investigators Todd Hollon of the University of Michigan and Shawn Hervey-Jumper from UCSF and co-researchers trained and validated FastGlioma to detect microscopic tumour infiltration in an international cohort of patients. They explain that “foundation modelling had not been previously investigated in studies on the clinical applications of SRH”, adding that they focused on tumour infiltration “as the most clinically important and ubiquitous problem in cancer surgery”.

The researchers trained FastGlioma using 11,462 whole-slide SRH images, divided into around four million unique 300×300 pixel SRH patches, acquired from 2799 patients undergoing surgery for suspected central nervous system tumours and/or epilepsy. They validated the model using a dataset of 3560 whole-slide images (852,000 patches) from 896 patients. Diagnostic classes of the dataset included normal brain, high-grade glioma, low-grade glioma, meningioma, pituitary adenoma, schwannoma and metastatic tumour. A subset of these had tumour infiltration categorized, ranging from normal brain to dense infiltration.

The researchers also developed a rapid visualization strategy, called few-shot visualizations. Based on FastGlioma’s self-supervised training, few-shot visualizations use a small support set of physician-selected SRH patch examples, representing a diverse selection of diffuse gliomas and normal brain parenchyma. By comparing feature similarity between the support set and the tissue sample being analysed, FastGlioma creates both a tumour-infiltration score and infiltration heat maps.

Prospective clinical testing

To test the fine-tuned FastGlioma model, three medical centres – UCSF, NYU Langone in New York City and the Medical University of Vienna – enrolled 220 patients with suspected diffuse gliomas who underwent tumour resection.

FastGlioma could detect and quantify the degree of tumour infiltration with an average accuracy of 92.1%. The tool maintained accurate tumour-infiltration scores despite significant cytological and histoarchitectural differences related to tumour grade, molecular genetics, treatment effect or WHO subtypes.

The primary end point for the study, reported in Nature, was to validate the accuracy and reproducibility of FastGlioma across various patient populations, demographics, medical centres and World Health Organization (WHO) diffuse glioma molecular subgroups. Additionally, the team aimed to compare the performance of FastGlioma with standard-of-care methods for intraoperative tumour-infiltration detection during brain tumour surgery.

To achieve this, the researchers evaluated FastGlioma as a surgical adjunct in a subset of 129 patients. Neurosurgeons sampled surgical margins at their discretion. Following SHR-imaging during the surgical procedure, the resected specimens were preserved for subsequent microscopic analysis. Expert neuropathologists scored each SRH image postoperatively to provide ground truth tumour-infiltration scores. FastGlioma significantly outperformed conventional methods, with only a 3.8% tumour miss rate, compared with a 24% miss rate for current standard-of-care surgical guidance methods.

Another benefit is that the analytic speed of FastGlioma provides a rapid and scalable alternative to conventional intraoperative pathology methods. The researchers point out that visual foundation models like FastGlioma also minimize reliance on radiographic features, contrast enhancement or extrinsic fluorescent labels to optimize the extent of resection.

The researchers also note that FastGlioma can accurately detect residual tumour for several non-glioma brain tumours, including paediatric brain tumours. “FastGlioma represents the transformative potential of medical foundation models to unlock the role of artificial intelligence in care of patients with cancer,” they write.

Future research will focus on applying a similar workflow to other human cancers, including lung, prostate, head-and-neck and breast cancer.

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A cutting-edge experiment that probes the internal structure of the neutron has been done at Jefferson Lab in the US. An international collaboration used the CEBAF Large Acceptance Spectrometer (CLAS12) to study the scattering of high-energy electrons from a deuterium target. The team measured generalized parton distributions, which provide a detailed picture of how the neutron’s constituent quarks contribute to its momentum and spin. A key innovation was the use of the Central Neutron Detector, a specialized instrument enabling the direct detection of neutrons ejected from the target.

“The theory of the strong force, called quantum chromodynamics [QCD], that describes the interaction between quarks via the exchange of gluons, is too complex and cannot be used to compute the properties of bound states, such as nucleons [both protons and neutrons],” explains Silvia Niccolai, a research director at the French National Centre for Scientific Research, who proposed the idea for the new detector. “Therefore, we need to use unknown but experimentally measurable functions called generalized parton distributions that help us connect the properties of the nucleons (for instance their spin) to the dynamics of quarks and gluons.”

The parton model assumes that a nucleon contains point-like constituents called partons – which represent the quarks and gluons of QCD.  By measuring parton distributions, physicists can examine correlations between a quark’s longitudinal momentum — how much of the nucleon’s total momentum it carries — and its transverse position within the nucleon. By analyzing these relationships for varying momentum values, scientists create a tomographic-like scan of the nucleon’s internal structure.

“This experiment is important because it directly accesses the structure of the neutron,” says Gerald Miller at the University of Washington, who was not involved in the study. “A neutron [outside of a nuclei] will decay in about 15 min, so it is difficult to study. The experiment in question used a novel technique to directly examine the neutron. They measured the neutron in the final state, which required new detection techniques.”

Separating quark contributions

Protons and neutrons consist of distinct combinations of up and down quarks: up-up-down for protons and down-down-up for neutrons. Each type of quark is associated with its own set of generalized parton distributions, and the overarching aim of the experimental effort is to determine distributions for both protons and neutrons. This would enable researchers to disentangle the distributions by quark type, offering deeper insights into the contributions of individual quark flavours to the properties of nucleons.

While these distributions are vital for understanding the strong interactions within both protons and neutrons, our understanding of protons is significantly more advanced. This disparity arises from the electric charge of protons, which facilitates their interaction with other charged particles, unlike electrically neutral neutrons. Additionally, proton targets are simpler to prepare, consisting solely of hydrogen atoms. In contrast, neutron experiments target deuterium nuclei, which comprise a neutron and a proton. The interaction between these two nucleons within the nucleus complicates the analysis of scattering data in neutron experiments.

To address these problems, the CLAS12 collaboration utilized the Central Neutron Detector, which was developed at France’s Laboratory of the Physics of the Two Infinities Irène Joliot-Curie (IJCLab). This allowed them to detect neutrons ejected from the deuterium target by high-energy electrons for the first time.

By combining neutron detection with the simultaneous measurement of scattered electrons and energetic photons produced during the interactions, the team gathered comprehensive data on particle momenta. This was used to calculate the generalized parton distributions of quarks inside neutrons.

Spin alignment

The CLAS12 team used electron beams with spins aligned both parallel and antiparallel to their momentum. This configuration resulted in slightly different interactions with the target, enabling the team to investigate subtle features of the generalized parton distributions related to angular momentum. By analyzing these details, they successfully disentangled the contributions of up and down quarks to the angular momentum of the neutron.

The team believes their findings could help address the longstanding “spin crisis“. This is the large body of experimental evidence suggesting that quarks and gluons contribute far less to the total spin of nucleons than initially expected.

“The sum of both the intrinsic spin of the quarks and gluons still doesn’t add up to the total spin,” says Adam Hobart, a researcher at IJCLab who led the data analysis for this experiment. “The only missing piece to complement the intrinsic spin of the quarks and the gluons is the orbital angular momentum of the quarks.”

The team plan to do a new and more accurate experiment that will involve firing electrons at a polarized target in which the nuclear spins of the deuterium all point in the same direction. This should allow the physicists to extract all possible generalized parton distributions from the scattering data.

“More data are needed to get a fuller picture, but this experiment can be thought of as a big step in a huge experimental program that is needed to get a complete understanding,” concludes Miller. “I think that this work will clearly influence future studies. Others will try to build on this experiment to expand the kinematic reach.”

The research is described in Physical Review Letters.

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When the Voyager 2 spacecraft flew past Uranus and Neptune in 1986 and 1989, it detected something strange: neither of these “ice giant” planets has a well-defined north and south magnetic pole. This absence has remained mysterious ever since, but simulations performed at the University of California, Berkeley (UCB) in the US have now suggested an explanation. According to UCB planetary scientist Burkhard Militzer, the disorganized magnetic fields of Uranus and Neptune may arise from a separation of the icy fluids that make up their interiors. The theory could be tested in laboratory experiments of fluids at high pressures, as well as by a proposed mission to Uranus in the 2040s.

On Earth, the dipole magnetic field that loops from the North Pole to the South Pole arises from convection in the planet’s liquid-iron outer core. Since Uranus and Neptune lack such a dipole field, this implies that the convective movement of material in their interiors must be very different.

In 2004, planetary scientists Sabine Stanley and Jeremy Bloxham suggested that the planets’ interiors might contain immiscible layers. This separation would make widespread convection impossible, preventing a global dipolar magnetic field from forming, while convection in just one layer would produce the disorganized magnetic field that Voyager 2 observed. However, the nature of these non-mixing layers was still unexplained – hampered, in part, by a lack of data.

“Since both planets have been visited by only one spacecraft (Voyager 2), we do not have many measurements to analyse,” Militzer says.

Two immiscible fluids

To investigate conditions deep beneath Uranus and Neptune’s icy surfaces, Militzer developed computer models to simulate how a mixture of water, methane and ammonia will behave at the temperatures (above 4750 K) and pressures (above 3 x 10⁶ atmospheres) that prevail there. The results surprised him. “One morning, I opened my laptop,” he recalls. “When I started analysing my latest simulations, I could not believe my eyes. An initially homogeneous mixture of water, methane and ammonia had separated into two distinct layers.”

The upper layer, he explains, is thin, rich in water and convecting, which allows it to generate the disordered magnetic field. The lower layer is magnetically inactive and composed of carbon, nitrogen and hydrogen. “This had never been observed before and I could tell right then that this result might allow us to understand what has been going on in the interiors of Uranus and Neptune,” he says.

A plastic polymer-like- and a water-rich layer

Militzer’s model, which he describes in PNAS, shows that the hydrogen content in the methane-ammonia mixture gradually decreases with depth, transforming into a C-N-H fluid. This C-N-H layer is almost like a plastic polymer, Militzer explains, and cannot support even a disorganized magnetic field – unlike the upper, water-rich layer, which likely convects.

A future mission to Uranus with the right instruments on board could provide observational evidence for this structure, Militzer says. “I would advocate for a Doppler imager so we can detect the planet’s natural oscillation frequencies,” he tells Physics World. Though such instruments are expensive and heavy, he says they are essential to detecting the presence of the predicted two ice layers in Uranus’ interior: “Like one can distinguish between an oboe and a clarinet, these frequencies can tell [us] about a planet’s interior structure.”

A follow-up to Voyager 2 could also reveal how the ice giants’ structures have evolved since they formed 4.5 billion years ago. Initially, their interiors would have contained only a single ice layer, and this layer would have generated a strong dipolar magnetic field with well-defined north and south poles. “Then, at some point, this ice separated into two distinct layers and their magnetic field switched from dipolar to disordered fields that we see today,” Militzer explains.

Determining when this switch occurred would help us understand not only Uranus and Neptune, but also ice giants orbiting stars other than our Sun. “The most common exoplanets discovered to date are around the same size as Uranus and Neptune, so when we observe the magnetic field of such ‘sub-Neptune’ exoplanets in the future, we might be able to say something about their age,” Militzer says.

In the near term, Militzer hopes that experimentalists will be able to test his theory in extremely-high temperatures and pressure fluid systems that mimic the proportions of elements found on Uranus and Neptune. But his long-term hopes are pinned on a new mission that could detect the predicted layers directly. “While I will have long retired when such a detection might eventually be made, I would be so happy to see it in my lifetime,” he says.

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