Category: Physics

Quantum computing offers the potential to solve complex problems faster than classical computers by leveraging the principles of quantum mechanics. Significant advancements have been made in areas, such as artificial intelligence, cryptography, deep learning, optimization, and solving complex equations.

While major technology companies like IBM, Google, and Microsoft are working toward practical quantum computers capable of handling larger quantum information, significant challenges remain before quantum technology can be widely adopted.

Although quantum communication and cryptography are increasingly used in commercial applications owing to their secure systems, quantum communication and cryptography must undergo rigorous verification for use in security-critical applications. These processes are essential to ensure no lapses in safety or security.

To address this gap, Assistant Professor Canh Minh Do, along with Associate Professor Tsubasa Takagi and Professor Kazuhiro Ogata from the Japan Advanced Institute of Science and Technology (JAIST), Japan, developed an automated approach to verify quantum programs based on Basic Dynamic Quantum Logic (BDQL).

BDQL faithfully captures quantum evolution and measurement in quantum mechanics, providing a logical framework to formalize and verify quantum protocols with their desired properties. Despite its effectiveness, BDQL had limitations, particularly its inability to handle interactions between participants in quantum protocols.

To overcome these limitations, the team has now developed a new logic known as Concurrent Dynamic Quantum Logic (CDQL), which extends BDQL’s capabilities to handle concurrency in quantum protocols.

In their study published on Dec. 12 in ACM Transactions on Software Engineering and Methodology, Dr. Do explains, “CDQL effectively formalizes concurrent behaviors and communication between participants in quantum protocols.

“Our logical framework also provides a transformation from CDQL models to BDQL models, ensuring compatibility with BDQL semantics, and introduces a lazy rewriting strategy for fast verification.”

This advancement not only enhances the expressiveness of the logic but also speeds up the verification process, making it applicable to a wider range of verified practical quantum applications.

One of the major advantages of CDQL over BDQL is its ability to handle concurrent actions. While BDQL was limited to sequential actions, CDQL can model quantum protocols that require multiple actions to occur concurrently, making it better suited for real-world problems.

Additionally, the framework provides a lazy rewriting strategy to improve the efficiency of the verification process. Concretely, this strategy eliminates irrelevant interleavings from earlier stages and reuses results to avoid needless computations.

This enhances the speed and scalability of verifying quantum protocols. Despite its advantages, our framework has some limitations, such as its inability to handle quantum data sharing over quantum channels. However, Dr. Do and his team plan to resolve this constraint in the future to increase CDQL’s versatility.

To improve the modeling and verification of quantum protocols, the CDQL has been developed as an extension of BDQL. The research team has successfully formalized and verified various quantum communication protocols in both BDQL and CDQL.

“Our automated formal verification approach, using both BDQL and CDQL, provides a rigorous framework for verifying both sequential and concurrent models of quantum protocols. This contributes to the reliability of foundational technologies such as quantum communication, quantum cryptography, and distributed quantum computing systems,” explains Dr. Do.

This work highlights the importance of ensuring the correctness of quantum protocols before they are deployed in critical applications.

In conclusion, CDQL is more effective than BDQL for formalizing quantum protocols with concurrent actions.

“This work introduces an automated approach using CDQL to verify the correctness of quantum protocols, ensuring their reliability before deployment in safety-critical and security-critical applications,” concludes Dr. Do.

He further adds, “By ensuring the correctness of quantum protocols, this work contributes to the development of reliable, bug-free quantum technologies, particularly in quantum communication and cryptography, over the next five to 10 years.”

This study represents a significant advancement in the formal verification of quantum protocols, contributing to the reliability, security, and practical applicability of quantum technologies.

More information: Canh Minh Do et al, Automated Quantum Protocol Verification Based on Concurrent Dynamic Quantum Logic, ACM Transactions on Software Engineering and Methodology (2024). DOI: 10.1145/3708475

Provided by Japan Advanced Institute of Science and Technology 

Neither gas nor liquid, supercritical fluids exhibit a unique mashup of the properties of both and arise when fluids are pushed to very high temperatures and pressures. Their properties make them ideal for a wide variety of chemical, pharmaceutical and environmental applications.

Supercritical carbon dioxide, for example, is often used to decaffeinate coffee—its liquid-like high density and gas-like rapid diffusion allows it to easily penetrate coffee beans and selectively extract the caffeine while preserving the beloved coffee taste.

In carbon capture and sequestration, carbon dioxide emissions are stored underground in their supercritical fluid form to combat climate change. It’s also found in rocket propulsion systems, because it can efficiently store a lot of energy, and the atmospheres of some planets, such as Venus. It could also be used as a more environmentally friendly fluid in future cooling systems.

Now, researchers at the Department of Energy’s SLAC National Accelerator Laboratory have uncovered new details of how supercritical fluids’ special properties arise from their molecular level dynamics. Their results are published in two studies in the journals Nature Communications and Physical Review Letters.

From static studies, researchers know that the molecular structure of supercritical fluids is made up of clusters of molecules of different sizes, but they haven’t been able to study the movement of these nanosized blobs until now.

“Probing these transient, fast-moving, nanoscale clusters is a challenge,” said Matthias Ihme, a professor of photon science at SLAC National Accelerator Laboratory, a professor of mechanical engineering at Stanford and a member of the Stanford PULSE Institute. The fact that supercritical fluids only form under high pressure and temperature further complicates their study, he said.

However, recent advances in X-ray free electron lasers allowed Ihme and his colleagues to use SLAC’s Linac Coherent Light Source (LCLS) to directly observe the ultrafast dynamics of molecular clusters in supercritical carbon dioxide. Those advances, said SLAC staff scientist Yanwen Sun, involved a decade-long effort to generate two bright, nearly identical LCLS X-ray flashes in rapid succession—making it possible to capture the kinds of dynamics Ihme and his team were interested in.

By measuring how the LCLS’s X-rays scattered off the samples over time, the authors found that the dynamics of these systems evolve within picoseconds, or trillionths of a second. Specifically, these results, published in Nature Communications, showed that the blobs transition from ballistic motion, which is relatively straight and predictable, to the more random and unpredictable Brownian motion.

However, Ihme said, “the existing theory does not capture these nanometer-length, picosecond-timescale dynamics,” so the team carried out follow-up molecular dynamics simulations. The simulations revealed that the observed transition in molecular dynamics is due to collisions between unbound, isolated molecules of the substance with its nanosized clusters.

“You can think of it like a molecular pinball machine, or billiards,” Ihme said. These collisions exchange momentum between the clusters, affecting the properties of the supercritical fluid such as heat capacity, density, and viscosity, which are directly related to how the fluid reacts and mixes, among other behaviors.

“Our measurements indicate that there are significant gaps in accurately predicting properties in these complex environments,” Ihme said.

Equipped with this novel insight, the team developed a theoretical model, published in Physical Review Letters, that connects these microscopic cluster dynamics with the macroscopic properties of supercritical fluids, potentially allowing researchers to predict and tailor them.

“This model is a tool that will allow us to better understand supercritical fluids, to better predict them, and ultimately to control them,” Ihme said. “That’s what an engineer or chemist needs for practical designs.”

In this work, the team focused solely on supercritical fluid carbon dioxide. Next, they hope to investigate the dynamics of supercritical water and the manipulation of chemical reactions in supercritical fluids, which could be used to break down harmful “forever chemicals” into harmless compounds or as environmentally benign solvents for green chemistry and catalytic applications.

More information: Arijit Majumdar et al, Direct observation of ultrafast cluster dynamics in supercritical carbon dioxide using X-ray Photon Correlation Spectroscopy, Nature Communications (2024). DOI: 10.1038/s41467-024-54782-1

Jingcun Fan et al, Heterogeneous Cluster Energetics and Nonlinear Thermodynamic Response in Supercritical Fluids, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.248001

Journal information: Physical Review Letters  , Nature Communications 

Provided by SLAC National Accelerator Laboratory 

When two probes orbiting the sun aligned with one another, researchers harnessed the opportunity to track the sun’s magnetic field as it traveled into the solar system. They found that the sharply oscillating magnetic field smooths out to gentle waves while accelerating the surrounding solar wind, according to a University of Michigan-led study published in The Astrophysical Journal.

The sharp S-shaped bends of the magnetic fields streaming out of the sun, called magnetic switchbacks, have long been of interest to solar scientists. Switchbacks impact the solar wind—the charged particles, or plasma, that stream from the sun and influence space weather in ways that can disrupt Earth’s electrical grids, radio waves, radar and satellites.

The new understanding of magnetic switchback changes over time will help improve solar wind forecasts to better predict space weather and its potential impacts on Earth.

“This study marks the first direct observation of switchback magnetic energy reducing with distance from the sun,” said Shirsh Soni, a research fellow of climate and space sciences engineering at the University of Michigan and corresponding author of the study.

The researchers pinpointed twelve time windows when the Parker Solar Probe and Solar Orbiter aligned. The Parker Solar Probe was positioned closest to the sun, less than 30 solar radii away (Rs)—a unit of distance based on the sun’s radius. The Solar Orbiter was further away at 130 Rs from the sun—nearing the orbit range of Venus which lies around 156 Rs.

Comparing magnetic field and plasma moment measurements collected from both spacecraft during these windows, the researchers traced the changes in magnetic switchbacks from one point to the next.

They found that switchback patches—bundles of sharp magnetic switchbacks—smoothed out into microstreams with 30% fewer magnetic reversals, while the background proton velocity increased by 10%, indicating acceleration of the surrounding solar wind.

The research team points to magnetic relaxation as the driving force of these changes. Essentially, as magnetic switchbacks travel outwards, the highly energetic switchbacks “relax,” transferring magnetic energy into kinetic energy to accelerate the surrounding plasma.

The next step is to track where and how the magnetic energy transfer occurs and whether it converts to thermal energy alongside kinetic energy. Magnetic switchbacks have been ruled out as a cause of the sun’s curiously hot corona, but could help solve another standing mystery of how the solar wind heats up as it travels through space.

“The collaboration between Parker Solar Probe and Solar Orbiter allows us to piece together this complex puzzle, marking a significant step forward in solar physics,” said Soni.

“Magnetic switchbacks are the fingerprints of the sun’s dynamic energy processes, revealing how it shapes the solar wind and, in turn, the entire solar system,” said Mojtaba Akhavan-Tafti, a U-M associate research scientist of climate and space sciences and engineering and co-corresponding author of the study.

Additional co-authors include Gabriel Ho Hin Suen and Christopher Owen of University College London; Justin Kasper of the University of Michigan; Marco Velli of the University of California, Los Angeles; and Rossana De Marco of the National Institute for Astrophysics and Institute for Space Astrophysics and Planetology in Rome, Italy.

More information: Shirsh Lata Soni et al, Switchback Patches Evolve into Microstreams via Magnetic Relaxation, The Astrophysical Journal (2024). DOI: 10.3847/1538-4357/ad94da

Journal information: Astrophysical Journal 

Provided by University of Michigan College of Engineering 

UNSW engineers have developed and built a special maser system that boosts microwave signals—such as those from deep space—but does not need to be super-cooled.

They say that diamonds are a girl’s best friend—but that might also soon be true for astronomers and astrophysicists following the new research. The team of quantum experts have developed a device known as a maser which uses a specially created purple diamond to amplify weak microwave signals, such as those which can come from deep space.

Most importantly, their maser works at room temperature, whereas previous such devices needed to be super-cooled, at great expense, down to about minus 269°C.

The amplified signals, originally emitted by pulsars, galaxies, or very distant spacecraft, could ultimately be crucial for expanding our understanding of the universe and fundamental physics.

The UNSW research team, led by Associate Professor Jarryd Pla, have published their findings in the journal Physical Review X, describing how a so-called spin system within the diamond can boost weak signals at room temperature.

“The microwaves enter the device and then the spins inside the diamond create copies of them, which in effect amplifies the microwave signals. Ideally, the microwave signals then come out much larger and with very little noise on top,” A/Prof. Pla says.

“Currently, electronic amplifiers are being used to detect signals from very distant spacecraft like Voyager 1 which is now more than 15 billion miles away from earth, but still sending out data.

“Those amplifiers are cryogenically cooled to reduce what is known as thermal noise, which is random electrical noise generated by the motion of electrons in the amplifier’s components. Otherwise, that noise would just overwhelm the signals being received.

“Our room temperature solid-state maser amplifier avoids all the complication and cost of having to cool everything down to extremely low temperatures and is also much more compact.”

In the paper, the researchers show their maser system can boost signals by a factor of up to 1,000.

Nitrogen vacancy center spins

The proof-of-concept maser developed by the UNSW team, which also includes Mr. Tom Day, lead author on the study, works by growing a diamond in a lab which contains imperfections known as nitrogen vacancy (NV) centers.

This NV is a deliberate defect where a nitrogen atom replaces a carbon atom next to an empty spot in the crystal structure, thereby creating a spin system.

When the spin system is placed inside a magnetic field and simultaneously exposed to a strong green laser beam, it is able to amplify incoming microwave signals..

As well as applications in space exploration, the room-temperature maser could also be hugely beneficial in defense applications, such as radar.

Radars work by sending out electromagnetic signals, which bounce off objects and return to the radar to provide information about the objects’ location, speed, and size. Being more easily able to detect and boost weak signals would therefore potentially be very useful.

Purple reigns

The research team acknowledge that further developments are needed to reduce noise in their maser system, but believe a commercial device could be operating within two to three years.

They are investigating the effect of increasing the concentration of NV-spins inside the diamond, as well as improving other components of the system, such as the resonator that the diamond sits in.

“In effect, we need to make the diamonds more purple,” says Mr. Day.

“The purple color is actually caused by red light emitted by the NV centers. Making darker samples means more NV centers, which ultimately produces higher levels of gain and lower levels of noise and makes the amplified signals clearer.

“However, if you grow these diamonds with very high densities of NV centers, then you can get unwanted defects, so that’s a materials engineering problem that we’re solving.”

A/Prof. Pla adds, “To be competitive against the current cryogenic amplifiers in terms of the low levels of noise then we know we need to boost the NV concentration in the diamond even further. And we think there is quite some way we can go, potentially up to an order of magnitude improvement there.

“We are also working with manufacturers from France and Japan to produce better resonators and we estimate that could also improve the noise by quite some margin.”

More information: Tom Day et al, Room-Temperature Solid-State Maser Amplifier, Physical Review X (2024). DOI: 10.1103/PhysRevX.14.041066

Journal information: Physical Review X 

Provided by University of New South Wales 

In-plane magnetic fields are responsible for inducing anomalous Hall effect in EuCd₂Sb₂ films, report researchers from the Institute of Science Tokyo. By studying how these fields change electronic structures, the team discovered a large in-plane anomalous Hall effect.

These findings, published in Physical Review Letters on December 3, 2024, pave the way for new strategies for controlling electronic transport under magnetic fields, potentially advancing applications in magnetic sensors.

The Hall effect is a fundamental phenomenon in material science. It occurs when a material carrying an electric current is exposed to a magnetic field, producing a voltage perpendicular to both the current and the magnetic field. This effect has been extensively studied in materials under out-of-plane magnetic fields. However, research on how in-plane magnetic fields induce this phenomenon has been very limited.

In recent years, in-plane magnetic fields have attracted growing interest due to their potential to unlock new material behaviors, particularly in materials with singular points in their electronic band structures, such as EuCd₂Sb₂.

Against this backdrop, a team of researchers from Institute of Science Tokyo and the RIKEN Center for Emergent Matter Science (CEMS), led by Associate Professor Masaki Uchida, explored how in-plane magnetic fields induce the anomalous Hall effect in EuCd₂Sb₂ films. Their study sheds light on how these fields induce a distinctive change in electronic band structures.

Uchida explains, “Our findings highlight a new way to manipulate the Hall effect in magnetic materials. This opens up exciting possibilities for future technologies that rely on precise magnetic field measurement, such as magnetic sensing.”

The team’s efforts revealed that in-plane magnetic fields lead to a significantly large anomalous Hall effect in EuCd₂Sb₂ thin films. This effect changes its sign with rotation of the in-plane magnetic field, exhibiting clear three-fold symmetry for rotation of the in-plane magnetic fields.

Furthermore, the study revealed that these effects are linked to an unusual out-of-plane shift of the singular points in electronic band structures. This shift corresponds to the manifestation of orbital magnetization, which is the rotational motion of an electron wave packet, formulated in modern terms as a quantum geometric tensor in solids.

This discovery deepens our understanding of how in-plane magnetic fields change the material’s internal structure.

The researchers also discovered that even small adjustments in the angle of the magnetic field could lead to significant variations in the in-plane anomalous Hall effect. This directional dependence further highlights the material’s versatility and its potential for use in technologies that require precise measurement of magnetic fields along specific directions.

Uchida concludes, “The present work not only heralds a breakthrough in experimentally studying orbital magnetization, but also stimulates materials development for future applications, revolutionizing the concept of the Hall effect ‘from out to in.'”

Overall, this study enhances our understanding of how in-plane magnetic fields influence the electronic properties of advanced materials, such as EuCd₂Sb₂, bringing us closer to developing materials with tailored magnetotransport properties for future technologies.

More information: Ayano Nakamura et al, In-Plane Anomalous Hall Effect Associated with Orbital Magnetization: Measurements of Low-Carrier Density Films of a Magnetic Weyl Semimetal, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.236602. On arXiv: DOI: 10.48550/arxiv.2405.16722

Journal information: Physical Review Letters  , arXiv 

Provided by Institute of Science Tokyo 

The future storage and processing of data stand to benefit greatly from tiny magnetic whirlpools known as skyrmions, which are robust against noise and may be useful in lower power consumption devices. The development of skyrmion-based technologies has received a boost from a simple and intuitive model for visualizing the complex motions of skyrmions developed by RIKEN researchers.

In addition to having mass and electric charge, electrons also possess spin—a form of intrinsic angular momentum.

In some crystalline materials, nearby electrons orient their spins relative to each other to form strange patterns. A skyrmion is one such example where the spin at the center points directly upward, while the surrounding spins gradually twist and point downwards to create a magnetic vortex.

As an electron moves through a lattice of skyrmions, its path bends due to the net (or “emergent”) magnetic field created by the skyrmions—a phenomenon known as the topological Hall effect. But this flow of electrons also causes the skyrmion lattice to move, resulting in an emergent electric field.

Given this complicated interplay, Max Birch and his colleagues at the RIKEN Center for Emergent Matter Science wanted to investigate what happens to the topological Hall effect when a skyrmion lattice moves.

The team chose the compound gadolinium palladium silicide (Gd₂PdSi₃) because its topological Hall effect is almost 100 times larger than those of similar materials. Their samples were also relatively small, making it easier to reach the high currents required to track skyrmion motion over micrometer length scales.

The researchers discovered that the skyrmion lattice motion totally canceled out the topological Hall effect. The paper is published in the journal Nature.

“It turns out that the topological Hall effect essentially scales with the velocity of the electrons relative to the skyrmions,” explains Birch. “Once the skyrmions reach the same velocity as the electrons, the topological Hall effect will vanish, since it is totally canceled out by the induced emergent electric field.”

An intuitive way of looking at this is that when the electrons and the skyrmions are moving at the same speed, their relative velocity is zero, and so there is no topological Hall effect.

Ironically, this demonstration on skyrmions, which are promising for forming the basis of future devices, means that they can be described by equations developed more than a century and a half ago. “We’ve shown that the topological effects can be expressed analogously to Maxwell’s equations of electromagnetism,” explains Birch.

This way of looking at skyrmion dynamics will be crucial for developing spintronic devices, the researchers believe.

More information: Max T. Birch et al, Dynamic transition and Galilean relativity of current-driven skyrmions, Nature (2024). DOI: 10.1038/s41586-024-07859-2

Journal information: Nature 

Provided by RIKEN 

Heating plasma to the ultra-high temperatures needed for fusion reactions requires more than turning the dial on a thermostat. Scientists consider multiple methods, one of which involves injecting electromagnetic waves into the plasma, the same process that heats food in microwave ovens. But when they produce one type of heating wave, they can sometimes simultaneously create another type of wave that does not heat the plasma, in effect wasting energy.

In response to the problem, scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have performed computer simulations confirming a technique that prevents the production of the unhelpful waves, known as slow modes, boosting the heat put into the plasma and increasing the efficiency of the fusion reactions.

“This is the first time scientists have used 2D computer simulations to explore how to reduce slow modes,” said Eun-Hwa Kim, a PPPL principal research physicist and lead author of the paper reporting the results in Physics of Plasmas. “The results could lead to more efficient plasma heating and possibly an easier path to fusion energy.”

The team, which included researchers from General Atomics who use the DIII-D tokamak fusion facility, determined that positioning a metal grate known as a Faraday screen at a slight five-degree slant with respect to the antenna producing the heating waves, also known as helicon waves, stops the production of the slow modes. Researchers want to avoid creating slow modes, because unlike helicon waves, they cannot penetrate the magnetic field lines confining the plasma to heat the core, where most fusion reactions occur. In addition, the slow modes are easily damped or snuffed out by the plasma itself. Therefore, any energy used to create slow modes is energy that is not used to heat the plasma and foster fusion reactions.

The researchers simulated the production of helicon waves and slow modes using the Petra-M computer code, a powerful and versatile program used to model electromagnetic waves in fusion devices and space plasmas. The simulations replicated conditions in the DIII-D tokamak, a doughnut-shaped plasma device operated by General Atomics for the DOE. The team performed a series of virtual experiments to test which of the following had the greatest effect on the production of slow modes—the antenna’s alignment, the Faraday screen’s alignment or the density of small particles known as electrons in front of the antenna.

The simulations confirmed suggestions made by previous researchers indicating that when the Faraday screen was aligned at an angle of five degrees or less from the orientation of the antenna, the screen—in effect—short-circuits the slow modes, making them fizzle out before they propagate into the plasma.

The suppression of slow modes depends greatly on how much the Faraday screen leans to the side.

“We found that when the screen’s orientation exceeds five degrees by only a little bit, the slow modes grow by a great deal,” said PPPL principal research physicist Masayuki Ono, one of the paper’s authors. “We were surprised by how sensitive the development of slow modes was to the screen alignment.”

Scientists could use this information to tweak the design of new fusion facilities to make their heating more powerful and efficient.

In the future, the scientists plan to increase their understanding of how to prevent slow modes by running computer simulations that consider more of the plasma’s properties and factor in more information about the antenna.

More information: E.-H. Kim et al, Full-wave simulations on helicon and parasitic excitation of slow waves near the edge plasma, Physics of Plasmas (2024). DOI: 10.1063/5.0222413

Journal information: Physics of Plasmas 

Provided by Princeton Plasma Physics Laboratory 

Figuring out certain aspects of a material’s electron structure can take a lot out of a computer—up to a million CPU hours, in fact. A team of Yale researchers, though, are using a type of artificial intelligence to make these calculations much faster and more accurately. Among other benefits, this makes it much easier to discover new materials. Their results are published in Nature Communications.

In the field of materials science, exploring the electronic structure of real materials is of particular interest, since it allows for better understanding of the physics of larger and more complex systems, such as moiré systems and defect states. Researchers typically will use a method known as density functional theory (DFT) to explore electronic structure, and for the most part it works fine.

“But the issue is that if you’re looking at excited state properties, like how materials behave when they interact with light or when they conduct electricity, then DFT really isn’t sufficient to understand the properties of the material,” said Prof. Diana Qiu, who led the study.

In that case, she said, researchers turn to higher-level theories that build on top of DFT. The problem for Qiu, though, is that her research focuses on problems that tend to be very computationally expensive. Sometimes, researchers will solve this by applying machine learning to their calculations. But it’s not much help in figuring out a material’s band structure, Qiu said, “which is what’s necessary to really understand the properties of the material.”

Qiu and her team decided to focus on the electrons’ wave function, which mathematically describes the quantum state of a particle. For the study, they used 2D materials, which are just a few atoms in thickness.

“We said ‘Okay, what is the wave function?'” said Qiu, assistant professor of mechanical engineering & materials science. “It’s this probability over space. We can always plot this as an image in space.”

They used a variational autoencoder, an AI image-processing tool, to create a dimensional representation of the wave function.

“This is done in what’s called an unsupervised way, so there’s no human guidance,” she said. “It takes this 100-gigabyte object and reduces it to 30 numbers, and those numbers represent the initial wave function. We then use that as the input for a second neural network that can then predict these more complicated excited state properties.”

Because the method avoids relying on intuition-based human guidance, it provides a more accurate representation. It’s also much more efficient and can be generalized for other applications.

“The representation that we can end up getting is also about 100 to 1,000 times smaller than what you need for feature selection,” she said. That’s important because the simpler the input, the better it can be used for other applications.

Qiu notes that conventional methods of calculating the band structure of something with three atoms could take between 100,000 and a million CPU hours. Their VAE-assisted method takes about an hour.

“The immediate practical application is that it gives us a way of really speeding up these complicated calculations, which means that now we can do these calculations for a wider range of materials, and that enables the discovery of new materials with properties that we care about.”

More information: Bowen Hou et al, Unsupervised representation learning of Kohn–Sham states and consequences for downstream predictions of many-body effects, Nature Communications (2024). DOI: 10.1038/s41467-024-53748-7

Journal information: Nature Communications 

Provided by Yale University 

Queen Mary University of London physicist Professor Chris White, along with his twin brother Professor Martin White from the University of Adelaide, have discovered a surprising connection between the Large Hadron Collider (LHC) and the future of quantum computing.

For decades, scientists have been striving to build quantum computers that leverage the bizarre laws of quantum mechanics to achieve far greater processing power than traditional computers. A recently identified property—amusingly called “magic”—is critical for building these machines, but its generation and enhancement remain a mystery.

For any given quantum system, magic is a measure that tells us how hard it is to calculate on a non-quantum computer. The higher the magic, the more we need quantum computers to describe the behavior. Studying the magic properties of quantum systems generates profound insights into the development and use of quantum computers.

This new research, published in Physical Review D, demonstrates for the first time that the LHC routinely produces “magic.” By studying the behavior of top quarks, the heaviest known fundamental particles, produced at the LHC, the researchers have predicted that “magic top quarks” will be made very often.

Interestingly, the amount of “magic” exhibited by these top quarks depends on how fast they are moving and their direction of travel, all of which can be measured by the ATLAS and CMS detectors that observe the results of the LHC proton collisions.

This discovery holds significant implications for understanding and potentially enhancing magic in other quantum systems. “While entanglement, where particles become linked, has been a major focus of quantum research,” explains Professor Chris White.

“Our work explores the concept of ‘magic’ in top quarks, which essentially measures how well-suited particles are for building powerful quantum computers.”

Professor Martin White adds, “The ATLAS experiment has already observed evidence of quantum entanglement. We have shown that the LHC can also observe more complex patterns of quantum behavior, at the highest energies yet attempted for these kinds of experiments.”

The potential benefits of quantum computers are vast, impacting fields like drug discovery and materials science. However, harnessing this power requires robust and controllable quantum states, and “magic” plays a critical role in achieving that control.

The White brothers’ research paves the way for a deeper understanding of the connection between quantum information theory and high-energy physics. “By studying ‘magic’ in top quark production,” Professor Chris White says, “we create a new bridge between these two exciting areas of physics.”

Furthermore, this research highlights the potential of the LHC as a unique platform for exploring the frontiers of quantum theory.

This discovery is not just about the heaviest particles in the universe; it’s about unlocking the potential of a revolutionary new computing paradigm.

More information: Chris D. White et al, Magic states of top quarks, Physical Review D (2024). DOI: 10.1103/PhysRevD.110.116016

Journal information: Physical Review D 

Provided by Queen Mary, University of London 

Quantum technologies are radically transforming our understanding of the universe. One emerging technology is macroscopic mechanical oscillators, devices that are vital in quartz watches, mobile phones, and lasers used in telecommunications. In the quantum realm, macroscopic oscillators could enable ultra-sensitive sensors and components for quantum computing, opening new possibilities for innovation in various industries.

Controlling mechanical oscillators at the quantum level is essential for developing future technologies in quantum computing and ultra-precise sensing. But controlling them collectively is challenging, as it requires near-perfect units, i.e., identical.

Most research in quantum optomechanics has centered on single oscillators, demonstrating quantum phenomena like ground-state cooling and quantum squeezing. But this hasn’t been the case for collective quantum behavior, where many oscillators act as one. Although these collective dynamics are key to creating more powerful quantum systems, they demand exceptionally precise control over multiple oscillators with nearly identical properties.

Scientists led by Tobias Kippenberg at EPFL have now achieved the long-sought goal: They successfully prepared six mechanical oscillators in a collective state, observed their quantum behavior, and measured phenomena that only emerge when oscillators act as a group. The research, published in Science, marks a significant step forward for quantum technologies, opening the door to large-scale quantum systems.

“This is enabled by the extremely low disorder among the mechanical frequencies in a superconducting platform, reaching levels as low as 0.1%,” says Mahdi Chegnizadeh, the first author of the study. “This precision allowed the oscillators to enter a collective state, where they behave as a unified system rather than independent components.”

To enable the observation of quantum effects, the scientists used sideband cooling, a technique that reduces the energy of oscillators to their quantum ground state—the lowest possible energy allowed by quantum mechanics.

Sideband cooling works by shining a laser at an oscillator, with the laser’s light tuned slightly below the oscillator‘s natural frequency. The light’s energy interacts with the vibrating system in a way that subtracts energy from it. This process is crucial for observing delicate quantum effects, as it reduces thermal vibrations and brings the system near stillness.

By increasing the coupling between the microwave cavity and the oscillators, the system transitions from individual to collective dynamics.

“More interestingly, by preparing the collective mode in its quantum ground state, we observed quantum sideband asymmetry, which is the hallmark of quantum collective motion. Typically, quantum motion is confined to a single object, but here it spanned the entire system of oscillators,” says Marco Scigliuzzo, a co-author of the study.

The researchers also observed enhanced cooling rates and the emergence of “dark” mechanical modes, i.e., modes that did not interact with the system’s cavity and retained higher energy.

The findings provide experimental confirmation of theories about collective quantum behavior in mechanical systems and open new possibilities for exploring quantum states. They also have major implications for the future of quantum technologies, as the ability to control collective quantum motion in mechanical systems could lead to advances in quantum sensing and generation of multi-partite entanglement.

All devices were fabricated in the Center of MicroNanoTechnology (CMi) at EPFL.

More information: Mahdi Chegnizadeh et al, Quantum collective motion of macroscopic mechanical oscillators, Science (2024). DOI: 10.1126/science.adr8187. www.science.org/doi/10.1126/science.adr8187

Journal information: Science 

Provided by Ecole Polytechnique Federale de Lausanne