Nonlocal correlations that define quantum entanglement could be reconciled with Einstein’s theory of relativity if space–time had two temporal dimensions. That is the implication of new theoretical work that extends nonlocal hidden variable theories of quantum entanglement and proposes a potential experimental test.

Marco Pettini, a theoretical physicist at Aix Marseille University in France, says the idea arose from conversations with the mathematical physicist Roger Penrose – who shared the 2020 Nobel Prize for Physics for showing that the general theory of relativity predicted black holes. “He told me that, from his point of view, quantum entanglement is the greatest mystery that we have in physics,” says Pettini. The puzzle is encapsulated by Bell’s inequality, which was derived in the mid-1960s by the Northern Irish physicist John Bell.

Bell’s breakthrough was inspired by the 1935 Einstein–Podolsky–Rosen paradox, a thought experiment in which entangled particles in quantum superpositions (using the language of modern quantum mechanics) travel to spatially separated observers Alice and Bob. They make measurements of the same observable property of their particles. As they are superposition states, the outcome of neither measurement is certain before it is made. However, as soon as Alice measures the state, the superposition collapses and Bob’s measurement is now fixed.

Quantum scepticism

A sceptic of quantum indeterminacy could hypothetically suggest that the entangled particles carried hidden variables all along, so that when Alice made her measurement, she simply found out the state that Bob would measure rather than actually altering it. If the observers are separated by a distance so great that information about the hidden variable’s state would have to travel faster than light between them, then hidden variable theory violates relativity. Bell derived an inequality showing the maximum degree of correlation between the measurements possible if each particle carried such a “local” hidden variable, and showed it was indeed violated by quantum mechanics.

A more sophisticated alternative investigated by the theoretical physicists David Bohm and his student Jeffrey Bub, as well as by Bell himself, is a nonlocal hidden variable. This postulates that the particle – including the hidden variable – is indeed in a superposition and defined by an evolving wavefunction. When Alice makes her measurement, this superposition collapses. Bob’s value then correlates with Alice’s. For decades, researchers believed the wavefunction collapse could travel faster than light without allowing superliminal exchange of information – therefore without violating the special theory of relativity. However, in 2012 researchers showed that any finite-speed collapse propagation would enable superluminal information transmission.

“I met Roger Penrose several times, and while talking with him I asked ‘Well, why couldn’t we exploit an extra time dimension?’,” recalls Pettini. Particles could have five-dimensional wavefunctions (three spatial, two temporal), and the collapse could propagate through the extra time dimension – allowing it to appear instantaneous. Pettini says that the problem Penrose foresaw was that this would enable time travel, and the consequent possibility that one could travel back through the “extra time” to kill one’s ancestors or otherwise violate causality. However, Pettini says he “recently found in the literature a paper which has inspired some relatively standard modifications of the metric of an enlarged space–time in which massive particles are confined with respect to the extra time dimension…Since we are made of massive particles, we don’t see it.”

Toy model

Pettini believes it might be possible to test this idea experimentally. In a new paper, he proposes a hypothetical experiment (which he describes as a toy model), in which two sources emit pairs of entangled, polarized photons simultaneously. The photons from one source are collected by recipients Alice and Bob, while the photons from the other source are collected by Eve and Tom using identical detectors. Alice and Eve compare the polarizations of the photons they detect. Alice’s photon must, by fundamental quantum mechanics, be entangled with Bob’s photon, and Eve’s with Tom’s, but otherwise simple quantum mechanics gives no reason to expect any entanglement in the system.

Pettini proposes, however, that Alice and Eve should be placed much closer together, and closer to the photon sources, than to the other observers. In this case, he suggests, the communication of entanglement through the extra time dimension when the wavefunction of Alice’s particle collapses, transmitting this to Bob, or when Eve’s particle is transmitted to Tom would also transmit information between the much closer identical particles received by the other woman. This could affect the interference between Alice’s and Eve’s photons and cause a violation of Bell’s inequality. “[Alice and Eve] would influence each other as if they were entangled,” says Pettini. “This would be the smoking gun.”

Bub, now a distinguished professor emeritus at the University of Maryland, College Park, is not holding his breath. “I’m intrigued by [Pettini] exploiting my old hidden variable paper with Bohm to develop his two-time model of entanglement, but to be frank I can’t see this going anywhere,” he says. “I don’t feel the pull to provide a causal explanation of entanglement, and I don’t any more think of the ‘collapse’ of the wave function as a dynamical process.” He says the central premise of Pettini’s – that adding an extra time dimension could allow the transmission of entanglement between otherwise unrelated photons, is “a big leap”. “Personally, I wouldn’t put any money on it,” he says.

The research is described in Physical Review Research.

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The world’s smallest pacemaker to date is smaller than a single grain of rice, optically controlled and dissolves after it’s no longer needed. According to researchers involved in the work, the pacemaker could work in human hearts of all sizes that need temporary pacing, including those of newborn babies with congenital heart defects.

“Our major motivation was children,” says Igor Efimov, a professor of medicine and biomedical engineering, in a press release from Northwestern University. Efimov co-led the research with Northwestern bioelectronics pioneer John Rogers.

“About 1% of children are born with congenital heart defects – regardless of whether they live in a low-resource or high-resource country,” Efimov explains. “Now, we can place this tiny pacemaker on a child’s heart and stimulate it with a soft, gentle, wearable device. And no additional surgery is necessary to remove it.”

The current clinical standard-of-care involves sewing pacemaker electrodes directly onto a patient’s heart muscle during surgery. Wires from the electrodes protrude from the patient’s chest and connect to an external pacing box. Placing the pacemakers – and removing them later – does not come without risk. Complications include infection, dislodgment, torn or damaged tissues, bleeding and blood clots.

To minimize these risks, the researchers sought to develop a dissolvable pacemaker, which they introduced in Nature Biotechnology in 2021. By varying the composition and thickness of materials in the devices, Rogers’ lab can control how long the pacemaker functions before dissolving. The dissolvable device also eliminates the need for bulky batteries and wires.

“The heart requires a tiny amount of electrical stimulation,” says Rogers in the Northwestern release. “By minimizing the size, we dramatically simplify the implantation procedures, we reduce trauma and risk to the patient, and, with the dissolvable nature of the device, we eliminate any need for secondary surgical extraction procedures.”

The latest iteration of the device – reported in Nature – advances the technology further. The pacemaker is paired with a small, soft, flexible, wireless device that is mounted onto the patient’s chest. The skin-interfaced device continuously captures electrocardiogram (ECG) data. When it detects an irregular heartbeat, it automatically shines a pulse of infrared light to activate the pacemaker and control the pacing.

“The new device is self-powered and optically controlled – totally different than our previous devices in those two essential aspects of engineering design,” says Rogers. “We moved away from wireless power transfer to enable operation, and we replaced RF wireless control strategies – both to eliminate the need for an antenna (the size-limiting component of the system) and to avoid the need for external RF power supply.”

Measurements demonstrated that the pacemaker – which is 1.8 mm wide, 3.5 mm long and 1 mm thick – delivers as much stimulation as a full-sized pacemaker. Initial studies in animals and in the human hearts of organ donors suggest that the device could work in human infants and adults. The devices are also versatile, the researchers say, and could be used across different regions of the heart or the body. They could also be integrated with other implantable devices for applications in nerve and bone healing, treating wounds and blocking pain.

The next steps for the research (supported by the Querrey Simpson Institute for Bioelectronics, the Leducq Foundation and the National Institutes of Health) include further engineering improvements to the device. “From the translational standpoint, we have put together a very early-stage startup company to work individually and/or in partnerships with larger companies to begin the process of designing the device for regulatory approval,” Rogers says.

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Harvard University is suing the Trump administration over its plan to block up to $9bn of government research grants to the institution. The suit, filed in a federal court on 21 April, claims that the administration’s “attempt to coerce and control” Harvard violates the academic freedom protected by the first amendment of the US constitution.

The action comes in the wake of the US administration claiming that Harvard and other universities have not protected Jewish students during pro-Gaza campus demonstrations. Columbia University has already agreed to change its teaching policies and clamp down on demonstrations in the hope of regaining some $400,000 of government grants.

Harvard president Alan Garber also sought negotiations with the administration on ways that it might satisfy its demands. But a letter sent to Garber dated 11 April, signed by three Trump administration officials, asserted that the university had “failed to live up to both the intellectual and civil rights conditions that justify federal investments”.

The letter demanded that Harvard reform and restructure its governance, stop all diversity, equality and inclusion (DEI) programmes and reform how it hires staff and students. It also said Harvard must stop recruiting international students who are “hostile to American values” and provide an audit on “viewpoint diversity” on admissions and hiring.

Some administration sources suggested that the letter, which effectively insists on government oversight of Harvard’s affairs, was an internal draft sent to Harvard by mistake. Nevertheless, Garber decided to end negotiations, leading Harvard to instead sue the government over the blocked funds.

We stand for the values that have made American higher education a beacon for the world

Alan Garber

A letter on 14 April from Harvard’s lawyers states that the university is “committed to fighting antisemitism and other forms of bigotry in its community”. It adds that it is “open to dialogue” about what it has done, and is planning to do, to “improve the experience of every member” of its community but concludes that Harvard “is not prepared to agree to demands that go beyond the lawful authority of this or any other administration”.

Writing in an open letter to the community dated 22 April, Garber says that “we stand for the values that have made American higher education a beacon for the world”. The administration has hit back by threatening to withdraw Harvard’s non-profit status, tax its endowment and jeopardise its ability to enrol overseas students, who currently make up more than 27% of its intake.

Budget woes

The Trump administration is also planning swingeing cuts to government science agencies. If its budget request for 2026 is approved by Congress, funding for NASA’s Science Mission Directorate would be almost halved from $7.3bn to $3.9bn. The Nancy Grace Roman Space Telescope, a successor to the Hubble and James Webb space telescopes, would be axed. Two missions to Venus – the DAVINCI atmosphere probe and the VERITAS surface-mapping project – as well as the Mars Sample Return mission would lose their funding too.

“The impacts of these proposed funding cuts would not only be devastating to the astronomical sciences community, but they would also have far-reaching consequences for the nation,” says Dara Norman, president of the American Astronomical Society. “These cuts will derail not only cutting-edge scientific advances, but also the training of the nation’s future STEM workforce.”

The National Oceanic and Atmospheric Administration (NOAA) also stands to lose key programmes, with the budget for its Ocean and Atmospheric Research Office slashed from $485m to just over $170m. Surviving programmes from the office, including research on tornado warning and ocean acidification, would move to the National Weather Service and National Ocean Service.

“This administration’s hostility toward research and rejection of climate science will have the consequence of eviscerating the weather forecasting capabilities that this plan claims to preserve,” says Zoe Lofgren, a senior Democrat who sits on the House of Representatives’ Science, Space, and Technology Committee.

The National Science Foundation (NSF), meanwhile, is unlikely to receive $234m for major building projects this financial year, which could spell the end of the Horizon supercomputer being built at the University of Texas at Austin. The NSF has already halved the number of graduate students in its research fellowship programme, while Science magazine says it is calling back all grant proposals that had been approved but not signed off, apparently to check that awardees conform to Trump’s stance on DEI.

A survey of 292 department chairs at US institutions in early April, carried out by the American Institute of Physics, reveals that almost half of respondents are experiencing or anticipate cuts in federal funding in the coming months. Entitled Impacts of Restrictions on Federal Grant Funding in Physics and Astronomy Graduate Programs, the report also says that the number of first-year graduate students in physics and astronomy is expected to drop by 13% in the next enrolment.

Update: 25/04/2025: Sethuraman Panchanathan has resigned as NSF director five years into his six-year term. Panchanathan took up the position in 2020 during Trump’s first term as US President. “I believe that I have done all I can to advance the mission of the agency and feel that it is time to pass the baton to new leadership,” Panchanathan said in a statement yesterday. “This is a pivotal moment for our nation in terms of global competitiveness. We must not lose our competitive edge.”

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Precise control over the generation of intense, ultrafast changes in magnetic fields called “magnetic steps” has been achieved by researchers in Hamburg, Germany. Using ultrashort laser pulses, Andrea Cavalleri and colleagues at the Max Planck Institute for the Structure and Dynamics of Matter disrupted the currents flowing through a superconducting disc. This alters the superconductor’s local magnetic environment on very short timescales – creating a magnetic step.

Magnetic steps rise to their peak intensity in just a few picoseconds, before decaying more slowly in several nanoseconds. They are useful to scientists because they rise and fall on timescales far shorter than the time it takes for materials to respond to external magnetic fields. As a result, magnetic steps could provide fundamental insights into the non-equilibrium properties of magnetic materials, and could also have practical applications in areas such as magnetic memory storage.

So far, however, progress in this field has been held back by technical difficulties in generating and controlling magnetic steps on ultrashort timescales. Previous strategies  have employed technologies including microcoils, specialized antennas, and circularly polarized light pulses. However, each of these schemes offer a limited degree of control over the properties of the magnetic steps they generated.

Quenching supercurrents

Now, Cavalleri’s team has developed a new technique that involves the quenching of currents in a superconductor. Normally, these “supercurrents” will flow indefinitely without losing energy, and will act to expel any external magnetic fields from the superconductor’s interior. However, if these currents are temporarily disrupted on ultrashort timescales, a sudden change will be triggered in the magnetic field close to the superconductor – which could be used to create a magnetic step.

To create this process, Cavalleri and colleagues applied ultrashort laser pulses to a thin, superconducting disc of yttrium barium copper oxide (YBCO), while also exposing the disc to an external magnetic field.

To detect whether magnetic steps had been generated, they placed a crystal of the semiconductor gallium phosphide in the superconductor’s vicinity. This material exhibits an extremely rapid Faraday response. This involves the rotation of the polarization of light passing through the semiconductor in response to changes in the local magnetic field. Crucially, this rotation can occur on sub-picosecond timescales.

In their experiments, researchers monitored changes to the polarization of an ultrashort “probe” laser pulse passing through the semiconductor shortly after they quenched supercurrents in their YBCO disc using a separate ultrashort “pump” laser pulse.

“By abruptly disrupting the material’s supercurrents using ultrashort laser pulses, we could generate ultrafast magnetic field steps with rise times of approximately one picosecond – or one trillionth of a second,” explains team member Gregor Jotzu.

Broadband step

This was used to generate an extremely broadband magnetic step, which contains frequencies ranging from sub-gigahertz to terahertz. In principle, this should make the technique suitable for studying magnetization in a diverse variety of materials.

To demonstrate practical applications, the team used these magnetic steps to control the magnetization of a ferrimagnet. Such a magnet has opposing magnetic moments, but has a non-zero spontaneous magnetization in zero magnetic field.

When they placed a ferrimagnet on top of their superconductor and created a magnetic step, the step field caused the ferrimagnet’s magnetization to rotate.

For now, the magnetic steps generated through this approach do not have the speed or amplitude needed to switch materials like a ferrimagnet between stable states. Yet through further tweaks to the geometry of their setup, the researchers are confident that this ability may not be far out of reach.

“Our goal is to create a universal, ultrafast stimulus that can switch any magnetic sample between stable magnetic states,” Cavalleri says. “With suitable improvements, we envision applications ranging from phase transition control to complete switching of magnetic order parameters.”

The research is described in Nature Photonics.

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Until now, researchers have had to choose between thermal and visible imaging: One reveals heat signatures while the other provides structural detail. Recording both and trying to align them manually — or harder still, synchronizing them temporally — can be inconsistent and time-consuming. The result is data that is close but never quite complete. The new FLIR MIX is a game changer, capturing and synchronizing high-speed thermal and visible imagery at up to 1000 fps. Visible and high-performance infrared cameras with FLIR Research Studio software work together to deliver one data set with perfect spatial and temporal alignment — no missed details or second guessing, just a complete picture of fast-moving events.

Jerry Beeney is a seasoned global business development leader with a proven track record of driving product growth and sales performance in the Teledyne FLIR Science and Automation verticals. With more than 20 years at Teledyne FLIR, he has played a pivotal role in launching new thermal imaging solutions, working closely with technical experts, product managers, and customers to align products with market demands and customer needs. Before assuming his current role, Beeney held a variety of technical and sales positions, including senior scientific segment engineer. In these roles, he managed strategic accounts and delivered training and product demonstrations for clients across diverse R&D and scientific research fields. Beeney’s dedication to achieving meaningful results and cultivating lasting client relationships remains a cornerstone of his professional approach.

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Researchers at the University of Victoria in Canada are developing a low-cost radiotherapy system for use in low- and middle-income countries and geographically remote rural regions. Initial performance characterization of the proof-of-concept device produced encouraging results, and the design team is now refining the system with the goal of clinical commercialization.

This could be good news for people living in low-resource settings, where access to cancer treatment is an urgent global health concern. The WHO’s International Agency for Research on Cancer estimates that there are at least 20 million new cases of cancer diagnosed annually and 9.7 million annual cancer-related deaths, based on 2022 data. By 2030, approximately 75% of cancer deaths are expected to occur in low- and middle-income countries, due to rising populations, healthcare and financial disparities, and a general lack of personnel and equipment resources compared with high-income countries.

The team’s orthovoltage radiotherapy system, known as KOALA (kilovoltage optimized alternative for adaptive therapy), is designed to create, optimize and deliver radiation treatments in a single session. The device, described in Biomedical Physics & Engineering Express, consists of a dual-robot system with a 225 kVp X-ray tube mounted onto one robotic arm and a flat-panel detector mounted on the other.

The same X-ray tube can be used to acquire cone-beam CT (CBCT) images, as well as to deliver treatment, with a peak tube voltage of 225 kVp and a maximum tube current of 2.65 mA for a 1.2 mm focal spot. Due to its maximum reach of 2.05 m and collision restrictions, the KOALA system has a limited range of motion, achieving 190° arcs for both CBCT acquisition and treatments.

Device testing

To characterize the KOALA system, lead author Olivia Masella and colleagues measured X-ray spectra for tube voltages of 120, 180 and 225 kVp. At 120 and 180 kVp, they observed good agreement with spectra from SpekPy (a Python software toolkit for modelling X-ray tube spectra). For the 225 kVp spectrum, they found a notable overestimation in the higher energies.

The researchers performed dosimetric tests by measuring percent depth dose (PDD) curves for a 120 kVp imaging beam and a 225 kVp therapy beam, using solid water phantom blocks with a Farmer ionization chamber at various depths. They used an open beam with 40° divergence and a source-to-surface distance of 30 cm. They also measured 2D dose profiles with radiochromic film at various depths in the phantom for a collimated 225 kVp therapy beam and a dose of approximately 175 mGy at the surface.

The PDD curves showed excellent agreement between experiment and simulations at both 120 and 225 kVp, with dose errors of less than 2%. The 2D profile results were less than optimal. The team aims to correct this by using a more optimal source-to-collimator distance (100 mm) and a custom-built motorized collimator.

Geometrical evaluation conducted using a coplanar star-shot test showed that the system demonstrated excellent geometrical accuracy, generating a wobble circle with a diameter of just 0.3 mm.

Low costs and clinical practicality

Principal investigator Magdalena Bazalova-Carter describes the rationale behind the KOALA’s development. “I began the computer simulations of this project about 15 years ago, but the idea originated from Michael Weil, a radiation oncologist in Northern California,” she tells Physics World. “He and our industrial partner, Tai-Nang Huang, the president of Linden Technologies, are overseeing the progress of the project. Our university team is diversified, working in medical physics, computer science, and electrical and mechanical engineering. Orimtech, a medical device manufacturer and collaborator, developed the CBCT acquisition and reconstruction software and built the imaging prototype.”

Masella says that the team is keeping costs low is various ways. “Megavoltage X-rays are most commonly used in conventional radiotherapy, but KOALA’s design utilizes low-energy kilovoltage X-rays for treatment. By using a 225 kVp X-ray tube, the X-ray generation alone is significantly cheaper compared to a conventional linac, at a cost of USD $150,000 compared to $3 million,” she explains. “By operating in the kilovoltage instead of megavoltage range, only about 4 mm of lead shielding is required, instead of 6 to 7 feet of high-density concrete, bringing the shielding cost down from $2 million to $50,000. We also have incorporated components that are much lower cost than [those in] a conventional radiotherapy system.”

“Our novel iris collimator leaves are only 1-mm thick due to the lower treatment X-ray beam energy, and its 12 leaves are driven by a single motor,” adds Bazalova-Carter. “Although multileaf collimators with 120 leaves utilized with megavoltage X-ray radiotherapy are able to create complex fields, they are about 8-cm thick and are controlled by 120 separate motors. Given the high cost and mechanical vulnerability of multileaf collimators, our single motor design offers a more robust and reliable alternative.”

The team is currently developing a new motorized collimator, an improved treatment couch and a treatment planning system. They plan to improve CBCT imaging quality with hardware modifications, develop a CBCT-to-synthetic CT machine learning algorithm, refine the auto-contouring tool and integrate all of the software to smooth the workflow.

The researchers are planning to work with veterinarians to test the KOALA system with dogs diagnosed with cancer. They will also develop quality assurance protocols specific to the KOALA device using a dog-head phantom.

“We hope to demonstrate the capabilities of our system by treating beloved pets for whom available cancer treatment might be cost-prohibitive. And while our system could become clinically adopted in veterinary medicine, our hope is that it will be used to treat people in regions where conventional radiotherapy treatment is insufficient to meet demand,” they say.

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Physicists working on the ATLAS experiment on the Large Hadron Collider (LHC) are the first to report the production of top quark–antiquark pairs in collisions involving heavy nuclei. By colliding lead ions, CERN’s LHC creates a fleeting state of matter called the quark–gluon plasma. This is an extremely hot and dense soup of subatomic particles that includes deconfined quarks and gluons. This plasma is believed to have filled the early universe microseconds after the Big Bang.

“Heavy-ion collisions at the LHC recreate the quark–gluon plasma in a laboratory setting,” Anthony Badea, a postdoctoral researcher at the University of Chicago and one of the lead authors of a paper describing the research. As well as boosting our understanding of the early universe, studying the quark–gluon plasma at the LHC could also provide insights into quantum chromodynamics (QCD), which is the theory of how quarks and gluons interact.

Although the quark–gluon plasma at the LHC vanishes after about 10^-23 s, scientists can study it by analysing how other particles produced in collisions move through it. The top quark is the heaviest known elementary particle and its short lifetime and distinct decay pattern offer a unique way to explore the quark–gluon plasma. This because the top quark decays before the quark–gluon plasma dissipates.

“The top quark decays into lighter particles that subsequently further decay,” explains Stefano Forte at the University of Milan, who was not involved in the research. “The time lag between these subsequent decays is modified if they happen within the quark–gluon plasma, and thus studying them has been suggested as a way to probe [quark–gluon plasma’s] structure. In order for this to be possible, the very first step is to know how many top quarks are produced in the first place, and determining this experimentally is what is done in this [ATLAS] study.”

First observations

The ATLAS team analysed data from lead–lead collisions and searched for events in which a top quark and its antimatter counterpart were produced. These particles can then decay in several different ways and the researchers focused on a less frequent but more easily identifiable mode known as the di-lepton channel. In this scenario, each top quark decays into a bottom quark and a W boson, which is a weak force-carrying particle that then transforms into a detectable lepton and an invisible neutrino.

The results not only confirmed that top quarks are created in this complex environment but also showed that their production rate matches predictions based on our current understanding of the strong nuclear force.

“This is a very important study,” says Juan Rojo, a theoretical physicist at the Free University of Amsterdam who did not take part in the research. “We have studied the production of top quarks, the heaviest known elementary particle, in the relatively simple proton–proton collisions for decades. This work represents the first time that we observe the production of these very heavy particles in a much more complex environment, with two lead nuclei colliding among them.”

As well as confirming QCD’s prediction of heavy-quark production in heavy-nuclei collisions, Rojo explains that “we have a novel probe to resolve the structure of the quark–gluon plasma”. He also says that future studies will enable us “to understand novel phenomena in the strong interactions such as how much gluons in a heavy nucleus differ from gluons within the proton”.

Crucial first step

“This is a first step – a crucial one – but further studies will require larger samples of top quark events to explore more subtle effects,” adds Rojo.

The number of top quarks created in the ATLAS lead–lead collisions agrees with theoretical expectations. In the future, more detailed measurements could help refine our understanding of how quarks and gluons behave inside nuclei. Eventually, physicists hope to use top quarks not just to confirm existing models, but to reveal entirely new features of the quark–gluon plasma.

Rojo says we could, “learn about the time structure of the quark–gluon plasma, measurements which are ‘finer’ would be better, but for this we need to wait until more data is collected, in particular during the upcoming high-luminosity run of the LHC”.

Badea agrees that ATLAS’s observation opens the door to deeper explorations. “As we collect more nuclei collision data and improve our understanding of top-quark processes in proton collisions, the future will open up exciting prospects”.

The research is described in Physical Review Letters.

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In the early days of quantum mechanics, physicists found its radical nature difficult to accept – even though the theory had successes. In particular Werner Heisenberg developed the first comprehensive formulation of quantum mechanics in 1925, while the following year Erwin Schrödinger was able to predict the spectrum of light emitted by hydrogen using his eponymous equation. Satisfying though these achievements were, there was trouble in store.

Long accustomed to Isaac Newton’s mechanical view of the universe, physicists had assumed that identical systems always evolve with time in exactly the same way, that is to say “deterministically”. But Heisenberg’s uncertainty principle and the probabilistic nature of Schrödinger’s wave function suggested worrying flaws in this notion. Those doubts were famously expressed by Albert Einstein, Boris Podolsky and Nathan Rosen in their “EPR” paper of 1935 (Phys. Rev. 47 777) and in debates between Einstein and Niels Bohr.

But the issues at stake went deeper than just a disagreement among physicists. They also touched on long-standing philosophical questions about whether we inhabit a deterministic universe, the related question of human free will, and the centrality of cause and effect. One person who rigorously addressed the questions raised by quantum theory was the German mathematician and philosopher Grete Hermann (1901–1984).

Hermann stands out in an era when it was rare for women to contribute to physics or philosophy, let alone to both. Writing in The Oxford Handbook of the History of Quantum Interpretations, published in 2022, the City University of New York philosopher of science Elise Crull has called Hermann’s work “one of the first, and finest, philosophical treatments of quantum mechanics”.

Grete Hermann upended the famous ‘proof’, developed by the Hungarian-American mathematician and physicist John von Neumann, that ‘hidden variables’ are impossible in quantum mechanics

What’s more, Hermann upended the famous “proof”, developed by the Hungarian-American mathematician and physicist John von Neumann, that “hidden variables” are impossible in quantum mechanics. But why have Hermann’s successes in studying the roots and meanings of quantum physics been so often overlooked? With 2025 being the International Year of Quantum Science and Technology, it’s time to find out.

Free thinker

Hermann was born on 2 March 1901 in the north German port city of Bremen. One of seven children, her mother was deeply religious, while her father was a merchant, a sailor and later an itinerant preacher. According to the 2016 book Grete Hermann: Between Physics and Philosophy by Crull and Guido Bacciagaluppi, she was raised according to her father’s maxim: “I train my children in freedom!” Essentially, he enabled Hermann to develop a wide range of interests and benefit from the best that the educational system could offer a woman at the time.

She was eventually admitted as one of a handful of girls at the Neue Gymnasium – a grammar school in Bremen – where she took a rigorous and broad programme of subjects. In 1921 Hermann earned a certificate to teach high-school pupils – an interest in education that reappeared in her later life – and began studying mathematics, physics and philosophy at the University of Göttingen.

In just four years, Hermann earned a PhD under the exceptional Göttingen mathematician Emmy Noether (1882–1935), famous for her groundbreaking theorem linking symmetry to physical conservation laws. Hermann’s final oral exam in 1925 featured not just mathematics, which was the subject of her PhD, but physics and philosophy too. She had specifically requested to be examined in the latter by the Göttingen philosopher Leonard Nelson, whose “logical sharpness” in lectures had impressed her.

By this time, Hermann’s interest in philosophy was starting to dominate her commitment to mathematics. Although Noether had found a mathematics position for her at the University of Freiburg, Hermann instead decided to become Nelson’s assistant, editing his books on philosophy. “She studies mathematics for four years,” Noether declared, “and suddenly she discovers her philosophical heart!”

Hermann found Nelson to be demanding and sometimes overbearing but benefitted from the challenges he set. “I gradually learnt to eke out, step by step,” she later declared, “the courage for truth that is necessary if one is to utterly place one’s trust, also within one’s own thinking, in a method of thought recognized as cogent.” Hermann, it appeared, was searching for a path to the internal discovery of truth, rather like Einstein’s Gedankenexperimente.

After Nelson died in 1927 aged just 45, Hermann stayed in Göttingen, where she continued editing and expanding his philosophical work and related political ideas. Espousing a form of socialism based on ethical reasoning to produce a just society, Nelson had co-founded a political action group and set up the associated Philosophical-Political Academy (PPA) to teach his ideas. Hermann contributed to both and also wrote for the PPA’s anti-Nazi newspaper.

Hermann’s involvement in the organizations Nelson had founded later saw her move to other locations in Germany, including Berlin. But after Hitler came to power in 1933, the Nazis banned the PPA, and Hermann and her socialist associates drew up plans to leave Germany. Initially, she lived at a PPA “school-in-exile” in neighbouring Denmark. As the Nazis began to arrest socialists, Hermann feared that Germany might occupy Denmark (as it indeed later did) and so moved again, first to Paris and then London.

Amid all these disruptions, Hermann continued to bring her dual philosophical and mathematical perspectives to physics, and especially to quantum mechanics

Arriving in Britain in early 1938, Hermann became acquainted with Edward Henry, another socialist, whom she later married. It was, however, merely a marriage of convenience that gave Hermann British citizenship and – when the Second World War started in 1939 – stopped her from being interned as an enemy alien. (The couple divorced after the war.) Amid all these disruptions, Hermann continued to bring her dual philosophical and mathematical perspectives to physics, and especially to quantum mechanics.

Mixing philosophy and physics

A major stimulus for Hermann’s work came from discussions she had in 1934 with Heisenberg and Carl Friedrich von Weizsäcker, who was then his research assistant at the Institute for Theoretical Physics in Leipzig. The previous year Hermann had written an essay entitled “Determinism and quantum mechanics”, which analysed whether the indeterminate nature of quantum mechanics – central to the “Copenhagen interpretation” of quantum behaviour – challenged the concept of causality.

Much cherished by physicists, causality says that every event has a cause, and that a given cause always produces a single specific event. Causality was also a tenet of the 18th-century German philosopher Immanuel Kant, best known for his famous 1781 treatise Critique of Pure Reason. He believed that causality is fundamental for how humans organize their experiences and make sense of the world.

Hermann, like Nelson, was a “neo-Kantian” who believed that Kant’s ideas should be treated with scientific rigour. In her 1933 essay, Hermann examined how the Copenhagen interpretation undermines Kant’s principle of causality. Although the article was not published at the time, she sent copies to Heisenberg, von Weizsäcker, Bohr and also Paul Dirac, who was then at the University of Cambridge in the UK.

In fact, we only know of the essay’s existence because Crull and Bacciagaluppi discovered a copy in Dirac’s archives at Churchill College, Cambridge. They also found a 1933 letter to Hermann from Gustav Heckmann, a physicist who said that Heisenberg, von Weizsäcker and Bohr had all read her essay and took it “absolutely and completely seriously”. Heisenberg added that Hermann was a “fabulously clever woman”.

Heckmann then advised Hermann to discuss her ideas more fully with Heisenberg, who he felt would be more open than Bohr to new ideas from an unexpected source. In 1934 Hermann visited Heisenberg and von Weizsäcker in Leipzig, with Heisenberg later describing his interaction in his 1971 memoir Physics and Beyond: Encounters and Conversations.

In that book, Heisenberg relates how rigorously Hermann wanted to treat philosophical questions. “[She] believed she could prove that the causal law – in the form Kant had given it – was unshakable,” Heisenberg recalled. “Now the new quantum mechanics seemed to be challenging the Kantian conception, and she had accordingly decided to fight the matter out with us.”

Their interaction was no fight, but a spirited discussion, with some sharp questioning from Hermann. When Heisenberg suggested, for instance, that a particular radium atom emitting an electron is an example of an unpredictable random event that has no cause, Hermann countered by saying that just because no cause has been found, it didn’t mean no such cause exists.

Significantly, this was a reference to what we now call “hidden variables” – the idea that quantum mechanics is being steered by additional parameters that we possibly don’t know anything about. Heisenberg then argued that even with such causes, knowing them would lead to complications in other experiments because of the wave nature of electrons.

Suppose, using a hidden variable, we could predict exactly which direction an electron would move. The electron wave wouldn’t then be able to split and interfere with itself, resulting in an extinction of the electron. But such electron interference effects are experimentally observed, which Heisenberg took as evidence that no additional hidden variables are needed to make quantum mechanics complete. Once again, Hermann pointed out a discrepancy in Heisenberg’s argument.

In the end, neither side fully convinced the other, but inroads were made, with Heisenberg concluding in his 1971 book that “we had all learned a good deal about the relationship between Kant’s philosophy and modern science”. Hermann herself paid tribute to Heisenberg in a 1935 paper “Natural-philosophical foundations of quantum mechanics”, which appeared in a relatively obscure philosophy journal called Abhandlungen der Fries’schen Schule (6 69). In it, she thanked Heisenberg “above all for his willingness to discuss the foundations of quantum mechanics, which was crucial in helping the present investigations”.

Quantum indeterminacy versus causality

In her 1933 paper, Hermann aimed to understand if the indeterminacy of quantum mechanics threatens causality. Her overall finding was that wherever indeterminacy is invoked in quantum mechanics, it is not logically essential to the theory. So without claiming that quantum theory actually supports causality, she left the possibility open that it might.

To illustrate her point, Hermann considered Heisenberg’s uncertainty principle, which says that there’s a limit to the accuracy with which complementary variables, such as position, q, and momentum, p, can be measured, namely ΔqΔp ≥ h where h is Planck’s constant. Does this principle, she wondered, truly indicate quantum indeterminism?

Hermann asserted that this relation can mean only one of two possible things. One is that measuring one variable leaves the value of the other undetermined. Alternatively, the result of measuring the other variable can’t be precisely predicted. Hermann dismissed the first option because its very statement implies that exact values exist, and so it cannot be logically used to argue against determinism. The second choice could be valid, but that does not exclude the possibility of finding new properties – hidden variables – that give an exact prediction.

Hermann used her mathematical training to point out a flaw in von Neumann’s 1932 famous proof, which said that no hidden-variable theory can ever reproduce the features of quantum mechanics

In making her argument about hidden variables, Hermann used her mathematical training to point out a flaw in von Neumann’s 1932 famous proof, which said that no hidden-variable theory can ever reproduce the features of quantum mechanics. Quantum mechanics, according to von Neumann, is complete and no extra deterministic features need to be added.

For decades, his result was cited as “proof” that any deterministic addition to quantum mechanics must be wrong. Indeed, von Neumann had such a well-deserved reputation as a brilliant mathematician that few people had ever bothered to scrutinize his analysis. But in 1964 the Northern Irish theorist John Bell famously showed that a valid hidden-variable theory could indeed exist, though only if it’s “non-local” (Physics 1 195).

Non-locality says that things can happen at different parts of the universe simultaneously without needing faster-than-light communication. Despite being a notion that Einstein never liked, non-locality has been widely confirmed experimentally. In fact, non-locality is a defining feature of quantum physics and one that’s eminently useful in quantum technology.

Then, in 1966 Bell examined von Neumann’s reasoning and found an error that decisively refuted the proof (Rev. Mod, Phys. 38 447). Bell, in other words, showed that quantum mechanics could permit hidden variables after all – a finding that opened the door to alternative interpretations of quantum mechanics. However, Hermann had reported the very same error in her 1933 paper, and again in her 1935 essay, with an especially lucid exposition that almost exactly foresees Bell’s objection.

She had got there first, more than three decades earlier (see box).

A new view of causality

After rebutting von Neumann’s proof in her 1935 essay, Hermann didn’t actually turn to hidden variables. Instead, Hermann went in a different and surprising direction, probably as a result of her discussions with Heisenberg. She accepted that quantum mechanics is a complete theory that makes only statistical predictions, but proposed an alternative view of causality within this interpretation.

We cannot foresee precise causal links in a quantum mechanics that is statistical, she wrote. But once a measurement has been made with a known result, we can work backwards to get a cause that led to that result. In fact, Hermann showed exactly how to do this with various examples. In this way, she maintains, quantum mechanics does not refute the general Kantian category of causality.

Not all philosophers have been satisfied by the idea of retroactive causality. But writing in The Oxford Handbook of the History of Quantum Interpretations, Crull says that Hermann “provides the contours of a neo-Kantian interpretation of quantum mechanics”. “With one foot squarely on Kant’s turf and the other squarely on Bohr’s and Heisenberg’s,” Crull concludes, “[Hermann’s] interpretation truly stands on unique ground.”

Grete Hermann’s 1935 paper shows a deep and subtle grasp of elements of the Copenhagen interpretation.

But Hermann’s 1935 paper did more than just upset von Neumann’s proof. In the article, she shows a deep and subtle grasp of elements of the Copenhagen interpretation such as its correspondence principle, which says that – in the limit of large quantum numbers – answers derived from quantum physics must approach those from classical physics.

The paper also shows that Hermann was fully aware – and indeed extended the meaning – of the implications of Heisenberg’s thought experiment that he used to illustrate the uncertainty principle. Heisenberg envisaged a photon colliding with an electron, but after that contact, she writes, the wave function of the physical system is a linear combination of terms, each being “the product of one wave function describing the electron and one describing the light quantum”.

As she went on to say, “The light quantum and the electron are thus not described each by itself, but only in their relation to each other. Each state of the one is associated with one of the other.” Remarkably, this amounts to an early perception of quantum entanglement, which Schrödinger described and named later in 1935. There is no evidence, however, that Schrödinger knew of Hermann’s insights.

Hermann’s legacy                             

On the centenary of the birth of a full theory of quantum mechanics, how should we remember Hermann? According to Crull, the early founders of quantum mechanics were “asking philosophical questions about the implications of their theory [but] none of these men were trained in both physics and philosophy”. Hermann, however, was an expert in the two. “[She] composed a brilliant philosophical analysis of quantum mechanics, as only one with her training and insight could have done,” Crull says.

Had Hermann’s 1935 paper been more widely known, it could have altered the early development of quantum mechanics

Sadly for Hermann, few physicists at the time were aware of her 1935 paper even though she had sent copies to some of them. Had it been more widely known, her paper could have altered the early development of quantum mechanics. Reading it today shows how Hermann’s style of incisive logical examination can bring new understanding.

Hermann leaves other legacies too. As the Second World War drew to a close, she started writing about the ethics of science, especially the way in which it was carried out under the Nazis. After the war, she returned to Germany, where she devoted herself to pedagogy and teacher training. She disseminated Nelson’s views as well as her own through the reconstituted PPA, and took on governmental positions where she worked to rebuild the German educational system, apparently to good effect according to contemporary testimony.

Hermann also became active in politics as an adviser to the Social Democratic Party. She continued to have an interest in quantum mechanics, but it is not clear how seriously she pursued it in later life, which saw her move back to Bremen to care for an ill comrade from her early socialist days.

Hermann’s achievements first came to light in 1974 when the physicist and historian Max Jammer revealed her 1935 critique of von Neumann’s proof in his book The Philosophy of Quantum Mechanics. Following Hermann’s death in Bremen on 15 April 1984, interest slowly grew, culminating in Crull and Bacciagaluppi’s 2016 landmark study Grete Hermann: Between Physics and Philosophy.

The life of this deep thinker, who also worked to educate others and to achieve worthy societal goals, remains an inspiration for any scientist or philosopher today.

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A few years ago, I wrote in Physics World about various bizarre structures I’d built from tennis balls, the most peculiar of which I termed “tennis-ball towers”. They consisted of a series of three-ball layers topped by a single ball (“the locker”) that keeps the whole tower intact. Each tower had (3n + 1) balls, where n is the number of triangular layers. The tallest tower I made was a seven-storey, 19-ball structure (n = 6). Shortly afterwards, I made an even bigger, nine-storey, 25-ball structure (n = 8).

Now, in the latest exciting development, I have built a new, record-breaking tower with 34 balls (n = 11), in which all 30 balls from the second to the eleventh layer are kept in equilibrium by the locker on the top (see photo a). The three balls in the bottom layer aren’t influenced by the locker as they stay in place by virtue of being on the horizontal surface of a table.

I tried going even higher but failed to build a structure that would stay intact without supporting “scaffolds”. Now in case you think I’ve just glued the balls together, watch the video below to see how the incredible 34-ball structure collapses spontaneously, probably due to a slight vibration as I walked around the table.

Even more unexpectedly, I have been able to make tennis-ball towers consisting of layers of four balls (4n + 1) and five balls too (5n + 1). Their equilibria are more delicate and, in the case of four-ball structures, so far I have only managed to build (photo b) a 21-ball, six-storey tower (n = 5). You can also see the tower in the video below.

The (5n + 1) towers are even trickier to make and (photo c) I have only got up to a three-storey structure with 11 balls (n = 2): two lots of five balls with a sixth single ball on top. In case you’re wondering, towers with six balls in each layer are physically impossible to build because they form a regular hexagon. You can’t just use another ball as a locker because it would simply sit between the other six (photo d).

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Researchers from the Karlsruhe Tritium Neutrino experiment (KATRIN) have announced the most precise upper limit yet on the neutrino’s mass. Thanks to new data and upgraded techniques, the new limit – 0.45 electron volts (eV) at 90% confidence – is half that of the previous tightest constraint, and marks a step toward answering one of particle physics’ longest-standing questions.

Neutrinos are ghostlike particles that barely interact with matter, slipping through the universe almost unnoticed. They come in three types, or flavours: electron, muon, and tau. For decades, physicists assumed all three were massless, but that changed in the late 1990s when experiments revealed that neutrinos can oscillate between flavours as they travel. This flavour-shifting behaviour is only possible if neutrinos have mass.

Although neutrino oscillation experiments confirmed that neutrinos have mass, and showed that the masses of the three flavours are different, they did not divulge the actual scale of these masses. Doing so requires an entirely different approach.

Looking for clues in electrons

In KATRIN’s case, that means focusing on a process called tritium beta decay, where a tritium nucleus (a proton and two neutrons) decays into a helium-3 nucleus (two protons and one neutron) by releasing an electron and an electron antineutrino. Due to energy conservation, the total energy from the decay is shared between the electron and the antineutrino. The neutrino’s mass determines the balance of the split.

“If the neutrino has even a tiny mass, it slightly lowers the energy that the electron can carry away,” explains Christoph Wiesinger, a physicist at the Technical University of Munich, Germany and a member of the KATRIN collaboration. “By measuring that [electron] spectrum with extreme precision, we can infer how heavy the neutrino is.”

Because the subtle effects of neutrino mass are most visible in decays where the neutrino carries away very little energy (most of it bound up in mass), KATRIN concentrates on measuring electrons that have taken the lion’s share. From these measurements, physicists can calculate neutrino mass without having to detect these notoriously weakly-interacting particles directly.

Improvements over previous results

The new neutrino mass limit is based on data taken between 2019 and 2021, with 259 days of operations yielding over 36 million electron measurements. “That’s six times more than the previous result,” Wiesinger says.

Other improvements include better temperature control in the tritium source and a new calibration method using a monoenergetic krypton source. “We were able to reduce background noise rates by a factor of two, which really helped the precision,” he adds.

At 0.45 eV, the new limit means the neutrino is at least a million times lighter than the electron. “This is a fundamental number,” Wiesinger says. “It tells us that neutrinos are the lightest known massive particles in the universe, and maybe that their mass has origins beyond the Standard Model.”

Despite the new tighter limit, however, definitive answers about the neutrino’s mass are still some ways off. “Neutrino oscillation experiments tell us that the lower bound on the neutrino mass is about 0.05 eV,” says Patrick Huber, a theoretical physicist at Virginia Tech, US, who was not involved in the experiment. “That’s still about 10 times smaller than the new KATRIN limit… For now, this result fits comfortably within what we expect from a Standard Model that includes neutrino mass.”

Model independence

Though Huber emphasizes that there are “no surprises” in the latest measurement, KATRIN has a key advantage over its rivals. Unlike cosmological methods, which infer neutrino mass based on how it affects the structure and evolution of the universe, KATRIN’s direct measurement is model-independent, relying only on energy and momentum conservation. “That makes it very powerful,” Wiesinger argues. “If another experiment sees a measurement in the future, it will be interesting to check if the observation matches something as clean as ours.”

KATRIN’s own measurements are ongoing, with the collaboration aiming for 1000 days of operations by the end of 2025 and a final sensitivity approaching 0.3 eV. Beyond that, the plan is to repurpose the instrument to search for sterile neutrinos – hypothetical heavier particles that don’t interact via the weak force and could be candidates for dark matter.

“We’re testing things like atomic tritium sources and ultra-precise energy detectors,” Wiesinger says. “There are exciting ideas, but it’s not yet clear what the next-generation experiment after KATRIN will look like.”

The research appears in Science.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Rigorous experiments

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

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

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

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

Giant atoms

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

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

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

Three important findings

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

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

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

The research is described in Physical Review Letters.

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

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

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

Cat on a hot tin…microwave cavity?

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

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

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

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

Benefits for quantum sensing and error correction

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

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

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

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

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

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

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

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

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

Intense flashes of light

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

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

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

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

Gold and platinum

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

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

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

Kilonova explosions

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

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

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

The research is described in The Astrophysical Journal.

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

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

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

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

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

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

Brain drain

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

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

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

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

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

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

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

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

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

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

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

High-fidelity quantum computing

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

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

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

Studying other problems

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

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

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

“We’ve gone through a shift”

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

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

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

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

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

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

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

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

Manipulative metasurfaces

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

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

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

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

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

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

Future challenges

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

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

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

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

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

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

Solar cell shading an issue for plant growth

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

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

A semi-transparent perovskite solar cell greenhouse

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

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

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

Low light conditions promote seedling growth

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

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

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

The research is published in Nature Communications.

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

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

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

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

Intrinsic energy density

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

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

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

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

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

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

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

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

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

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

Dark energy takes over

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

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

Scalar quantum field

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

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

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

“Big rip” avoided

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

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

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

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

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Physicists in the UK have drawn up plans for an International Year of Classical Physics (IYC) in 2027 – exactly three centuries after the death of Isaac Newton. Following successful international years devoted to astronomy (2009), light (2015) and quantum science (2025), they want more recognition for a branch of physics that underpins much of everyday life.

A bright green Flower of Kent apple has now been picked as the official IYC logo in tribute to Newton, who is seen as the “father of classical physics”. Newton, who died in 1727, famously developed our understanding of gravity – one of the fundamental forces of nature – after watching an apple fall from a tree of that variety in his home town of Woolsthorpe, Lincolnshire, in 1666.

“Gravity is central to classical physics and contributes an estimated $270bn to the global economy,” says Crispin McIntosh-Smith, chief classical physicist at the University of Lincoln. “Whether it’s rockets escaping Earth’s pull or skiing down a mountain slope, gravity is loads more important than quantum physics.”

McIntosh-Smith, who also works in cosmology having developed the Cosmic Crisp theory of the universe during his PhD, will now be leading attempts to get endorsement for IYC from the United Nations. He is set to take a 10-strong delegation from Bramley, Surrey, to Paris later this month.

An official gala launch ceremony is being pencilled in for the Travelodge in Grantham, which is the closest hotel to Newton’s birthplace. A parallel scientific workshop will take place in the grounds of Woolsthorpe Manor, with a plenary lecture from TV physicist Brian Cox. Evening entertainment will feature a jazz band.

Numerous outreach events are planned for the year, including the world’s largest demonstration of a wooden block on a ramp balanced by a crate on a pulley. It will involve schoolchildren pouring Golden Delicious apples into the crate to illustrate Newton’s laws of motion. Physicists will also be attempting to break the record for the tallest tower of stacked Braeburn apples.

But there is envy from those behind the 2025 International Year of Quantum Science and Technology. “Of course, classical physics is important but we fear this year will peel attention away from the game-changing impact of quantum physics,” says Anne Oyd from the start-up firm Qrunch, who insists she will only play a cameo role in events. “I believe the impact of classical physics is over-hyped.”

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FLASH irradiation, an emerging cancer treatment that delivers radiation at ultrahigh dose rates, has been shown to significantly reduce acute skin toxicity in laboratory mice compared with conventional radiotherapy. Having demonstrated this effect using proton-based FLASH treatments, researchers from Aarhus University in Denmark have now repeated their investigations using electron-based FLASH (eFLASH).

Reporting their findings in Radiotherapy and Oncology, the researchers note a “remarkable similarity” between eFLASH and proton FLASH with respect to acute skin sparing.

Principal investigator Brita Singers Sørensen and colleagues quantified the dose–response modification of eFLASH irradiation for acute skin toxicity and late fibrotic toxicity in mice, using similar experimental designs to those previously employed for their proton FLASH study. This enabled the researchers to make direct quantitative comparisons of acute skin response between electrons and protons. They also compared the effectiveness of the two modalities to determine whether radiobiological differences were observed.

Over four months, the team examined 197 female mice across five irradiation experiments. After being weighed, earmarked and given an ID number, each mouse was randomized to receive either eFLASH irradiation (average dose rate of 233 Gy/s) or conventional electron radiotherapy (average dose rate of 0.162 Gy/s) at various doses.

For the treatment, two unanaesthetized mice (one from each group) were restrained in a jig with their right legs placed in a water bath and irradiated by a horizontal 16 MeV electron beam. The animals were placed on opposite sides of the field centre and irradiated simultaneously, with their legs at a 3.2 cm water-equivalent depth, corresponding to the dose maximum.

The researchers used a diamond detector to measure the absolute dose at the target position in the water bath and assumed that the mouse foot target received the same dose. The resulting foot doses were 19.2–57.6 Gy for eFLASH treatments and 19.4–43.7 Gy for conventional radiotherapy, chosen to cover the entire range of acute skin response.

FLASH confers skin protection

To evaluate the animals’ response to irradiation, the researchers assessed acute skin damage daily from seven to 28 days post-irradiation using an established assay. They weighed the mice weekly, and one of three observers blinded to previous grades and treatment regimens assessed skin toxicity. Photographs were taken whenever possible. Skin damage was also graded using an automated deep-learning model, generating a dose–response curve independent of observer assessments.

The researchers also assessed radiation-induced fibrosis in the leg joint, biweekly from weeks nine to 52 post-irradiation. They defined radiation-induced fibrosis as a permanent reduction of leg extensibility by 75% or more in the irradiated leg compared with the untreated left leg.

To assess the tissue-sparing effect of eFLASH, the researchers used dose–response curves to derive TD₅₀ – the toxic dose eliciting a skin response in 50% of mice. They then determined a dose modification factor (DMF), defined as the ratio of eFLASH TD₅₀ to conventional TD_50. A DMF larger than one suggests that eFLASH reduces toxicity.

The eFLASH treatments had a DMF of 1.45–1.54 – in other words, a 45–54% higher dose was needed to cause comparable skin toxicity to that caused by conventional radiotherapy. “The DMF indicated a considerable acute skin sparing effect of eFLASH irradiation,” the team explain. Radiation-induced fibrosis was also reduced using eFLASH, with a DMF of 1.15.

For DMF-based equivalent doses, the development of skin toxicity over time was similar for eFLASH and conventional treatments, throughout the dose groups. This supports the hypothesis that eFLASH modifies the dose–response rather than causing a changed biological mechanism. The team also suggests that the difference in DMF seen for fibrotic response and acute skin damage suggests that FLASH sparing depends on tissue type and might be specific to acute and late-responding tissue.

Similar skin damage between electrons and protons

Sørensen and colleagues compared their findings to previous studies of normal-tissue damage from proton irradiation, both in the entrance plateau and using the spread-out Bragg peak (SOBP). DMF values for electrons (1.45–1.54) were similar to those of transmission protons (1.44–1.50) and slightly higher than for SOBP protons (1.35–1.40). “Despite dose rate and pulse structure differences, the response to electron irradiation showed substantial similarity to transmission and SOBP damage,” they write.

Although the average eFLASH dose rate (233 Gy/s) was higher than that of the proton studies (80 and 60 Gy/s), it did not appear to influence the biological response. This supports the hypothesis that beyond a certain dose rate threshold, the tissue-sparing effect of FLASH does not increase notably.

The researchers point out that previous studies also found biological similarities in the FLASH effect for electrons and protons, with this latest work adding data on similar comparable and quantifiable effects. They add, however, that “based on the data of this study alone, we cannot say that the biological response is identical, nor that the electron and proton irradiation elicit the same biological mechanisms for DNA damage and repair. This data only suggests a similar biological response in the skin.”

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Last year the UK government placed a new cap of £9535 on annual tuition fees, a figure that will likely rise in the coming years as universities tackle a funding crisis. Indeed, shortfalls are already affecting institutions, with some saying they will run out of money in the next few years. The past couple of months alone have seen several universities announce plans to shed academic staff and even shut departments.

Whether you agree with tuition fees or not, the fact is that students will continue to pay a significant sum for a university education. Value for money is part of the university proposition and lecturers can play a role by conveying the excitement of their chosen field. But what are the key requirements to help do so? In the late 1990s we carried out a study aimed at improving the long-term performance of students who initially struggled with university-level physics.

With funding from the Higher Education Funding Council for Wales, the study involved structured interviews with 28 students and 17 staff. An internal report – The Rough Guide to Lecturing – was written which, while not published, informed the teaching strategy of Cardiff University’s physics department for the next quarter of a century.

From the findings we concluded that lecture courses can be significantly enhanced by simply focusing on three principles, which we dub the three “E”s. The first “E” is enthusiasm. If a lecturer appears bored with the subject – perhaps they have given the same course for many years – why should their students be interested? This might sound obvious, but a bit of reading, or examining the latest research, can do wonders to freshen up a lecture that has been given many times before.

For both old and new courses it is usually possible to highlight at least one research current paper in a semester’s lectures. Students are not going to understand all of the paper, but that is not the point – it is the sharing in contemporary progress that will elicit excitement. Commenting on a nifty experiment in the work, or the elegance of the theory, can help to inspire both teacher and student.

As well as freshening up the lecture course’s content, another tip is to mention the wider context of the subject being taught, perhaps by mentioning its history or possible exciting applications. Be inventive –we have evidence of a lecturer “live” translating parts of Louis de Broglie’s classic 1925 paper “La relation du quantum et la relativité” during a lecture. It may seem unlikely, but the students responded rather well to that.

Supporting students

The second “E” is engagement. The role of the lecturer as a guide is obvious, but it should also be emphasized that the learner’s desire is to share the lecturer’s passion for, and mastery of, a subject. Styles of lecturing and visual aids can vary greatly between people, but the important thing is to keep students thinking.

Don’t succumb to the apocryphal definition of a lecture as only a means of transferring the lecturer’s notes to the student’s pad without first passing through the minds of either person. In our study, when the students were asked “What do you expect from a lecture?”, they responded simply to learn something new, but we might extend this to a desire to learn how to do something new.

Simple demonstrations can be effective for engagement. Large foam dice, for example, can illustrate the non-commutation of 3D rotations. Fidget-spinners in the hands of students can help explain the vector nature of angular momentum. Lecturers should also ask rhetorical questions that make students think, but do not expect or demand answers, particularly in large classes.

More importantly, if a student asks a question, never insult them – there is no such thing as a “stupid” question. After all, what may seem a trivial point could eliminate a major conceptual block for them. If you cannot answer a technical query, admit it and say you will find out for next time – but make sure you do. Indeed, seeing that the lecturer has to work at the subject too can be very encouraging for students.

The final “E” is enablement. Make sure that students have access to supporting material. This could be additional notes; a carefully curated reading list of papers and books; or sets of suitable interesting problems with hints for solutions, worked examples they can follow, and previous exam papers. Explain what amount of self-study will be needed if they are going to benefit from the course.

Have clear and accessible statements concerning the course content and learning outcomes – in particular, what students will be expected to be able to do as a result of their learning. In our study, the general feeling was that a limited amount of continuous assessment (10–20% of the total lecture course mark) encourages both participation and overall achievement, provided students are given good feedback to help them improve.

Next time you are planning to teach a new course, or looking through those decades-old notes, remember enthusiasm, engagement and enablement. It’s not rocket science, but it will certainly help the students learn it.

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Researchers in China have unveiled a 105-qubit quantum processor that can solve in minutes a quantum computation problem that would take billions of years using the world’s most powerful classical supercomputers. The result sets a new benchmark for claims of so-called “quantum advantage”, though some previous claims have faded after classical algorithms improved.

The fundamental promise of quantum computation is that it will reduce the computational resources required to solve certain problems. More precisely, it promises to reduce the rate at which resource requirements grow as problems become more complex. Evidence that a quantum computer can solve a problem faster than a classical computer – quantum advantage – is therefore a key measure of success.

The first claim of quantum advantage came in 2019, when researchers at Google reported that their 53-qubit Sycamore processor had solved a problem known as random circuit sampling (RCS) in just 200 seconds. Xiaobu Zhu, a physicist at the University of Science and Technology of China (USTC) in Hefei who co-led the latest work, describes RCS as follows: “First, you initialize all the qubits, then you run them in single-qubit and two-qubit gates and finally you read them out,” he says. “Since this process includes every key element of quantum computing, such as initializing the gate operations and readout, unless you have really good fidelity at each step you cannot demonstrate quantum advantage.”

At the time, the Google team claimed that the best supercomputers would take 10::000 years to solve this problem. However, subsequent improvements to classical algorithms reduced this to less than 15 seconds. This pattern has continued ever since, with experimentalists pushing quantum computing forward even as information theorists make quantum advantage harder to achieve by improving techniques used to simulate quantum algorithms on classical computers.

Recent claims of quantum advantage

In October 2024, Google researchers announced that their 67-qubit Sycamore processor had solved an RCS problem that would take an estimated 3600 years for the Frontier supercomputer at the US’s Oak Ridge National Laboratory to complete. In the latest work, published in Physical Review Letters, Jian-Wei Pan, Zhu and colleagues set the bar even higher. They show that their new Zuchongzhi 3.0 processor can complete in minutes an RCS calculation that they estimate would take Frontier billions of years using the best classical algorithms currently available.

To achieve this, they redesigned the readout circuit of their earlier Zuchongzhi processor to improve its efficiency, modified the structures of the qubits to increase their coherence times and increased the total number of superconducting qubits to 105. “We really upgraded every aspect and some parts of it were redesigned,” Zhu says.

Google’s latest processor, Willow, also uses 105 superconducting qubits, and in December 2024 researchers there announced that they had used it to demonstrate quantum error correction. This achievement, together with complementary advances in Rydberg atom qubits from Harvard University’s Mikhail Lukin and colleagues, was named Physics World’s Breakthrough of the Year in 2024. However, Zhu notes that Google has not yet produced any peer-reviewed research on using Willow for RCS, making it hard to compare the two systems directly.

The USTC team now plans to demonstrate quantum error correction on Zuchongzhi 3.0. This will involve using an error correction code such as the surface code to combine multiple physical qubits into a single “logical qubit” that is robust to errors.  “The requirements for error-correction readout are much more difficult than for RCS,” Zhu notes. “RCS only needs one readout, whereas error-correction needs readout many times with very short readout times…Nevertheless, RCS can be a benchmark to show we have the tools to run the surface code. I hope that, in my lab, within a few months we can demonstrate a good-quality error correction code.”

“How progress gets made”

Quantum information theorist Bill Fefferman of the University of Chicago in the US praises the USTC team’s work, describing it as “how progress gets made”. However, he offers two caveats. The first is that recent demonstrations of quantum advantage do not have efficient classical verification schemes – meaning, in effect, that classical computers cannot check the quantum computer’s work. While the USTC researchers simulated a smaller problem on both classical and quantum computers and checked that the answers matched, Fefferman doesn’t think this is sufficient. “With the current experiments, at the moment you can’t simulate it efficiently, the verification doesn’t work anymore,” he says.

The second caveat is that the rigorous hardness arguments proving that the classical computational power needed to solve an RCS problem grows exponentially with the problem’s complexity apply only to situations with no noise. This is far from the case in today’s quantum computers, and Fefferman says this loophole has been exploited in many past quantum advantage experiments.

Still, he is upbeat about the field’s prospects. “The fact that the original estimates the experimentalists gave did not match some future algorithm’s performance is not a failure: I see that as progress on all fronts,” he says. “The theorists are learning more and more about how these systems work and improving their simulation algorithms and, based on that, the experimentalists are making their systems better and better.”

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Sometimes, you just have to follow your instincts and let serendipity take care of the rest.

North Ronaldsay, a remote island north of mainland Orkney, has a population of about 50 and a lot of sheep. In the early 19th century, it thrived on the kelp ash industry, producing sodium carbonate (soda ash), potassium salts and iodine for soap and glass making.

But when cheaper alternatives became available, the island turned to its unique breed of seaweed-eating sheep. In 1832 islanders built a 12-mile-long dry stone wall around the island to keep the sheep on the shore, preserving inland pasture for crops.

My connection with North Ronaldsay began last summer when my partner, Sue Bowler, and I volunteered for the island’s Sheep Festival, where teams of like minded people rebuild sections of the crumbling wall. That experience made us all the more excited when we learned that North Ronaldsay also had a science festival.

This year’s event took place on 14–16 March and getting there was no small undertaking. From our base in Leeds, the journey involved a 500-mile drive to a ferry, a crossing to Orkney mainland, and finally, a flight in a light aircraft. With just 50 inhabitants, we had no idea how many people would turn up but instinct told us it was worth the trip.

Sue, who works for the Royal Astronomical Society (RAS), presented Back to the Moon, while together we ran hands-on maker activities, a geology walk and a trip to the lighthouse, where we explored light beams and Fresnel lenses.

The Yorkshire Branch of the Institute of Physics (IOP) provided laser-cut hoist kits to demonstrate levers and concepts like mechanical advantage, while the RAS shared Connecting the Dots – a modern LED circuit version of a Victorian after-dinner card set illustrating constellations.

Despite the island’s small size, the festival drew attendees from neighbouring islands, with 56 people participating in person and another 41 joining online. Across multiple events, the total accumulated attendance reached 314.

One thing I’ve always believed in science communication is to listen to your audience and never make assumptions. Orkney has a rich history of radio and maritime communications, shaped in part by the strategic importance of Scapa Flow during the Second World War.

The Orkney Wireless Museum is a testament to this legacy, and one of our festival guests had even reconstructed a working 1930s Baird television receiver for the museum.

Leaving North Ronaldsay was hard. The festival sparked fascinating conversations, and I hope we inspired a few young minds to explore physics and astronomy.

• The author would like to thanks Alexandra Wright (festival organizer), Lucinda Offer (education, outreach and events officer at the RAS) and Sue Bowler (editor of Astronomy & Geophysics)

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Analysing circulating tumour cells (CTCs) in the blood could help scientists detect cancer in the body. But separating CTCs from blood is a difficult, laborious process and requires large sample volumes.

Researchers at the K N Toosi University of Technology (KNTU) in Tehran, Iran believe that ultrasonic waves could separate CTCs from red blood cells accurately, in an energy efficient way and in real time. They publish their study in the journal Physics of Fluids.

“In a broader sense, we asked: ‘How can we design a microfluidic, lab-on-a-chip device powered by SAWs [standing acoustic waves] that remains simple enough for medical experts to use easily, while still delivering precise and efficient cell separation?’,” says senior author Naser Naserifar, an assistant professor in mechanical engineering at KNTU. “We became interested in acoustofluidics because it offers strong, biocompatible forces that effectively handle cells with minimal damage.”

Acoustic waves can deliver enough force to move cells over small distances without damaging them. The researchers used dual pressure acoustic fields at critical positions in a microchannel to separate CTCs from other cells. The CTCs are gathered at an outlet for further analyses, cultures and laboratory procedures.

In the process of designing the chip, the researchers integrated computational modelling, experimental analysis and artificial intelligence (AI) algorithms to analyse acoustofluidic phenomena and generate datasets that predict CTC migration in the body.

“We introduced an acoustofluidic microchannel with two optimized acoustic zones, enabling fast, accurate separation of CTCs from RBCs [red blood cells],” explains Afshin Kouhkord, who performed the work while a master’s student in the Advance Research in Micro And Nano Systems Lab at KNTU. “Despite the added complexity under the hood, the resulting chip is designed for simple operation in a clinical environment.”

So far, the researchers have evaluated the device with numerical simulations and tested it using a physical prototype. Simulations modelled fluid flow, acoustic pressure fields and particle trajectories. The physical prototype was made of lithium niobate, with polystyrene microspheres used as surrogates for red blood cells and CTCs. Results from the prototype agreed with numerical simulations to within 3.5%.

“This innovative approach in laboratory-on-chip technology paves the way for personalized medicine, real-time molecular analysis and point-of-care diagnostics,” Kouhkord and Naserifar write.

The researchers are now refining their design, aiming for a portable device that could be operated with a small battery pack in resource-limited and remote environments.

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