QT/ New quantum ruler to explore exotic matter
Quantum news biweekly vol.61, 12th October — 26th October
TL;DR
- Researchers have developed a ‘quantum ruler’ to measure and explore the strange properties of multilayered sheets of graphene, a form of carbon. The work may also lead to a new, miniaturized standard for electrical resistance that could calibrate electronic devices directly on the factory floor, eliminating the need to send them to an off-site standards laboratory.
- Understanding the interplay between consciousness, energy and matter could bring important insights into our fundamental understanding of reality.
- Scientists have theoretically predicted that light can be bent under pseudogravity. A recent study by researchers using photonic crystals has demonstrated this phenomenon. This breakthrough has significant implications for optics, materials science, and the development of 6G communications.
- Physicists have shown that simulating models of hypothetical time travel can solve experimental problems that appear impossible to solve using standard physics.
- Researchers have long been exploring the effect of using tailored laser drives to manipulate the properties of quantum materials away from equilibrium. One of the most striking demonstrations of this physics has been in unconventional superconductors, where signatures of enhanced electronic coherences and super-transport have been documented in the resulting non-equilibrium states. However, these phenomena have not yet been systematically studied or optimized, primarily due to the complexity of the experiments. Technological applications are therefore still far removed from reality. In a recent experiment, this same group of researchers discovered a far more efficient way to create a previously observed metastable, superconducting-like state in K3C60 using laser light.
- The interaction between solid matter and positron (the antiparticle of the electron) has provided important insights across a variety of disciplines, including atomic physics, materials science, elementary particle physics, and medicine. However, the experimental generation of positronic compounds by a bombardment of positrons onto surfaces has proved challenging. In a new study, researchers detect molecular ion desorption from the surface of an ionic crystal when bombarded with positrons and propose a model based on positronic compound generation to explain their results.
- Applying machine learning to find the properties of atomic pieces of geometry shows how AI has the power to accelerate discoveries in maths.
- Scientists unveil exciting possibilities for the development of highly efficient quantum devices.
- For the first time, in a unique laboratory experiment at CERN, researchers have observed individual atoms of antihydrogen fall under the effects of gravity. In confirming antimatter and regular matter are gravitationally attracted, the finding rules out gravitational repulsion as the reason why antimatter is largely missing from the observable universe.
- Negative pressure is a rare and challenging-to-detect phenomenon in physics. Using liquid-filled optical fibers and sound waves, researchers have now discovered a new method to measure it. The research group gain important insights into thermodynamic states.
Quantum Computing Market
According to the recent market research report ‘Quantum Computing Market with COVID-19 impact by Offering (Systems and Services), Deployment (On Premises and Cloud Based), Application, Technology, End-use Industry and Region — Global Forecast to 2026’, published by MarketsandMarkets, the Quantum Computing market is expected to grow from USD 472 million in 2021 to USD 1,765 million by 2026, at a CAGR of 30.2%. The early adoption of quantum computing in the banking and finance sector is expected to fuel the growth of the market globally. Other key factors contributing to the growth of the quantum computing market include rising investments by governments of different countries to carry out research and development activities related to quantum computing technology. Several companies are focusing on the adoption of QCaaS post-COVID-19. This, in turn, is expected to contribute to the growth of the quantum computing market. However, stability and error correction issues are expected to restrain the growth of the market.
According to ‘Quantum Computing Market Research Report: By Offering, Deployment Type, Application, Technology, Industry — Industry Share, Growth, Drivers, Trends and Demand Forecast to 2030’ report, the quantum computing market is projected to reach $64,988 million by 2030. Machine learning (ML) is expected to progress at the highest CAGR, during the forecast period, among all application categories, owing to the fact that quantum computing is being integrated in ML for improving the latter’s use case.
Latest Research
A Quantum Ruler for Orbital Magnetism in Moiré Quantum Matter
by M.R. Slot, Y. Maximenko, P.M. Haney, S. Kim, D.T. Walkup, E. Strelcov, Son T. Le, E.M. Shih, D. Yildiz, S.R. Blankenship, K. Watanabe, T. Taniguchi, Y. Barlas, N.B. Zhitenev, F. Ghahari and J.A. Stroscio in Science
A single-atom-thick sheet of carbon known as graphene has remarkable properties on its own, but things can get even more interesting when you stack up multiple sheets. When two or more overlying sheets of graphene are sightly misaligned — twisted at certain angles relative to each other — they take on a plethora of exotic identities.Depending on the twist angle, these materials, known as moiré quantum matter, can suddenly generate their own magnetic fields, become superconductors with zero electrical resistance, or conversely, turn into perfect insulators.
Joseph A. Stroscio and his colleagues at the National Institute of Standards and Technology (NIST), along with an international team of collaborators, have developed a “quantum ruler” to measure and explore the strange properties of these twisted materials. The work may also lead to a new, miniaturized standard for electrical resistance that could calibrate electronic devices directly on the factory floor, eliminating the need to send them to an off-site standards laboratory.
Collaborator Fereshte Ghahari, a physicist from George Mason University in Fairfax, Virginia, took two layers of graphene (known as bilayer graphene) of about 20 micrometers across and twisted them relative to another two layers to create a moiré quantum matter device. Ghahari made the device using the nanofabrication facility at NIST’s Center for Nanoscale Science and Technology. NIST researchers Marlou Slot and Yulia Maximenko then chilled this twisted material device to one-hundredth of a degree above absolute zero, reducing random motions of atoms and electrons and heightening the ability for electrons in the material to interact. After reaching ultralow temperatures, they examined how the energy levels of electrons in the layers of graphene changed when they varied the strength of a strong external magnetic field. Measuring and manipulating the energy levels of electrons is critical for designing and manufacturing semiconductor devices.
To measure the energy levels, the team used a versatile scanning tunneling microscope that Stroscio designed and built at NIST. When the researchers applied a voltage to the graphene bilayers in the magnetic field, the microscope recorded the tiny current from the electrons that “tunneled” out from the material to the microscope probe tip.
In a magnetic field, electrons move in circular paths. Ordinarily, the circular orbits of the electrons in solid materials have a special relationship with an applied magnetic field: The area enclosed by each circular orbit, multiplied by the applied field, can only take on a set of fixed, discrete values, due to the quantum nature of electrons. In order to maintain that fixed product, if the magnetic field is halved, then the area enclosed by an orbiting electron must double. The difference in energy between successive energy levels that follow this pattern can be used like tick marks on a ruler to measure the material’s electronic and magnetic properties. Any subtle deviation from this pattern would represent a new quantum ruler that can reflect the orbital magnetic properties of the particular quantum moiré material researchers are studying.
In fact, when the NIST researchers varied the magnetic field applied to the moiré graphene bilayers, they found evidence of a new quantum ruler at play. The area enclosed by the circular orbit of electrons multiplied by the applied magnetic field no longer equaled a fixed value. Instead, the product of those two numbers had shifted by an amount dependent on the magnetization of the bilayers. This deviation translated into a set of different tick marks for the energy levels of the electrons. The findings promise to shed new light on how electrons confined to twisted sheets of graphene give rise to new magnetic properties.
“Using the new quantum ruler to study how the circular orbits vary with magnetic field, we hope to reveal the subtle magnetic properties of these moiré quantum materials,” Stroscio said.
In moiré quantum materials, electrons have a range of possible energies — highs and lows, shaped like an egg carton — that are determined by the electric field of the materials. The electrons are concentrated in the lower energy states, or valleys, of the carton. The large spacing between the valleys in the bilayers, bigger than the atomic spacing in any single layer of graphene or multiple layers that aren’t twisted, accounts for some of the unusual magnetic properties the team found, said NIST theoretical physicist Paul Haney. The researchers, including colleagues from the University of Maryland in College Park and the Joint Quantum Institute, a research partnership between NIST and the University of Maryland, described their work in the new aricle.
Because the properties of moiré quantum matter can be chosen by selecting a specific twist angle and number of atomically thin layers, the new measurements promise to provide a deeper understanding of how scientists can tailor and optimize the magnetic and electronic properties of quantum materials for a host of applications in microelectronics and related fields. For instance, ultrathin superconductors are already known to be exquisitely sensitive detectors of single photons, and quantum moiré superconductors rank among the very thinnest.
The NIST team also has an interest in another application: Under the right conditions, moiré quantum matter may provide a new, easier to use standard for electrical resistance. The present standard is based on the discrete resistance values that a material takes on when a strong magnetic field is applied to the electrons in a two-dimensional layer. This phenomenon, known as the quantum Hall effect, originates from the same quantized energy levels of the electrons in the circular orbits discussed above. The discrete resistance values can be used to calibrate the resistance in various electrical devices. But because a hefty magnetic field is needed, the calibrations can only be conducted at a metrology facility such as NIST.
If researchers could manipulate quantum moiré matter so that it has a net magnetization even in the absence of an external applied magnetic field, Stroscio said, then it could potentially be used to create a new portable version of the most precise standard for resistance, known as the anomalous quantum Hall resistance standard. Calibrations of electronic devices could be performed at the manufacturing site, potentially saving millions of dollars.
Unifying matter, energy and consciousness
by Mahendra Samarawickrama in AIP (the American Institute of Physics) Conference Proceedings
With the rise of brain-interface technology and artificial intelligence that can imitate brain functions, understanding the nature of consciousness and how it interacts with reality is not just an age-old philosophical question but also a salient challenge for humanity.
Can AI become conscious, and how would we know? Should we incorporate human or animal cells, such as neurons, into machines and robots? Would they be conscious and have subjective experiences? Does consciousness reduce to physicalism, or is it fundamental? And if machine-brain interaction influenced you to commit a crime, or caused a crime, would you be responsible beyond a reasonable doubt? Do we have a free will?
AI and computer science specialist Dr Mahendra Samarawickrama, winner of the Australian Computer Society’s Information and Communications Technology (ICT) Professional of the year, has applied his knowledge of physics and artificial neural networks to this thorny topic. He presented a peer-reviewed paper on fundamental physics and consciousness at the 11th International Conference on Mathematical Modelling in Physical Sciences, Unifying Matter, Energy and Consciousness, which has just been published in the AIP (the American Institute of Physics) Conference Proceedings.
“Consciousness is an evolving topic connected to physics, engineering, neuroscience and many other fields. Understanding the interplay between consciousness, energy and matter could bring important insights to our fundamental understanding of reality,” said Dr Samarawickrama.
“Einstein’s dream of a unified theory is a quest that occupies the minds of many theoretical physicists and engineers. Some solutions completely change existing frameworks, which increases complexity and creates more problems than it solves.
“My theory brings the notion of consciousness to fundamental physics such that it complements the current physics models and explains the time, causality, and interplay of consciousness, energy and matter.
“I propose that consciousness is a high-speed sequential flow of awareness subjected to relativity. The quantised energy of consciousness can interplay with matter creating reality while adhering to laws of physics, including quantum physics and relativity.
“Awareness can be seen in life, AI and even physical realities like entangled particles. Studying consciousness helps us be aware of and differentiate realities that exist in nature,” he said.
Dr Samarawickrama is an honorary Visiting Scholar in the School of Computer Science at the University of Technology Sydney, where he has contributed to UTS research on data science and AI, focusing on social impact.
“Research in this field could pave the way towards the development of conscious AI, with robots that are aware and have the ability to think becoming a reality. We want to ensure that artificial intelligence is ethical and responsible in emerging solutions,” Dr Samarawickrama said.
Deflection of electromagnetic waves by pseudogravity in distorted photonic crystals
by Kanji Nanjyo, Yuki Kawamoto, Hitoshi Kitagawa, Daniel Headland, Masayuki Fujita, Kyoko Kitamura in Physical Review
A collaborative group of researchers has manipulated the behavior of light as if it were under the influence of gravity. The findings have far-reaching implications for the world of optics and materials science, and bear significance for the development of 6G communications.
Albert Einstein’s theory of relativity has long established that the trajectory of electromagnetic waves — including light and terahertz electromagnetic waves — can be deflected by gravitational fields.
Scientists have recently theoretically predicted that replicating the effects of gravity — i.e., pseudogravity — is possible by deforming crystals in the lower normalized energy (or frequency) region.
“We set out to explore whether lattice distortion in photonic crystals can produce pseudogravity effects,” said Professor Kyoko Kitamura from Tohoku University’s Graduate School of Engineering.
Photonic crystals possess unique properties that enable scientists to manipulate and control the behavior of light, serving as ‘traffic controllers’ for light within crystals. They are constructed by periodically arranging two or more different materials with varying abilities to interact with and slow down light in a regular, repeating pattern. Furthermore, pseudogravity effects due to adiabatic changes have been observed in photonic crystals.
Kitamura and her colleagues modified photonic crystals by introducing lattice distortion: gradual deformation of the regular spacing of elements, which disrupted the grid-like pattern of protonic crystals. This manipulated the photonic band structure of the crystals, resulting in a curved beam trajectory in-medium — just like a light-ray passing by a massive celestial body such as a black hole.
Specifically, they employed a silicon distorted photonic crystal with a primal lattice constant of 200 micrometers and terahertz waves. Experiments successfully demonstrated the deflection of these waves.
“Much like gravity bends the trajectory of objects, we came up with a means to bend light within certain materials,” adds Kitamura. “Such in-plane beam steering within the terahertz range could be harnessed in 6G communication. Academically, the findings show that photonic crystals could harness gravitational effects, opening new pathways within the field of graviton physics,” said Associate Professor Masayuki Fujita from Osaka University.
Nonclassical Advantage in Metrology Established via Quantum Simulations of Hypothetical Closed Timelike Curves
by David R. M. Arvidsson-Shukur, Aidan G. McConnell, Nicole Yunger Halpern in Physical Review Letters
Physicists have shown that simulating models of hypothetical time travel can solve experimental problems that appear impossible to solve using standard physics.
If gamblers, investors and quantum experimentalists could bend the arrow of time, their advantage would be significantly higher, leading to significantly better outcomes.
Researchers at the University of Cambridge have shown that by manipulating entanglement — a feature of quantum theory that causes particles to be intrinsically linked — they can simulate what could happen if one could travel backwards in time. So that gamblers, investors and quantum experimentalists could, in some cases, retroactively change their past actions and improve their outcomes in the present.
Whether particles can travel backwards in time is a controversial topic among physicists, even though scientists have previously simulated models of how such spacetime loops could behave if they did exist. By connecting their new theory to quantum metrology, which uses quantum theory to make highly sensitive measurements, the Cambridge team has shown that entanglement can solve problems that otherwise seem impossible.
“Imagine that you want to send a gift to someone: you need to send it on day one to make sure it arrives on day three,” said lead author David Arvidsson-Shukur, from the Cambridge Hitachi Laboratory. “However, you only receive that person’s wish list on day two. So, in this chronology-respecting scenario, it’s impossible for you to know in advance what they will want as a gift and to make sure you send the right one.
“Now imagine you can change what you send on day one with the information from the wish list received on day two. Our simulation uses quantum entanglement manipulation to show how you could retroactively change your previous actions to ensure the final outcome is the one you want.”
The simulation is based on quantum entanglement, which consists of strong correlations that quantum particles can share and classical particles — those governed by everyday physics — cannot. The particularity of quantum physics is that if two particles are close enough to each other to interact, they can stay connected even when separated. This is the basis of quantum computing — the harnessing of connected particles to perform computations too complex for classical computers.
“In our proposal, an experimentalist entangles two particles,” said co-author Nicole Yunger Halpern, researcher at the National Institute of Standards and Technology (NIST) and the University of Maryland. “The first particle is then sent to be used in an experiment. Upon gaining new information, the experimentalist manipulates the second particle to effectively alter the first particle’s past state, changing the outcome of the experiment.”
“The effect is remarkable, but it happens only one time out of four!” said Arvidsson-Shukur. “In other words, the simulation has a 75% chance of failure. But the good news is that you know if you have failed. If we stay with our gift analogy, one out of four times, the gift will be the desired one (for example a pair of trousers), another time it will be a pair of trousers but in the wrong size, or the wrong colour, or it will be a jacket.”
To give their model relevance to technologies, the theorists connected it to quantum metrology. In a common quantum metrology experiment, photons — small particles of light — are shone onto a sample of interest and then registered with a special type of camera. If this experiment is to be efficient, the photons must be prepared in a certain way before they reach the sample. The researchers have shown that even if they learn how to best prepare the photons only after the photons have reached the sample, they can use simulations of time travel to retroactively change the original photons.
To counteract the high chance of failure, the theorists propose to send a huge number of entangled photons, knowing that some will eventually carry the correct, updated information. Then they would use a filter to ensure that the right photons pass to the camera, while the filter rejects the rest of the ‘bad’ photons.
“Consider our earlier analogy about gifts,” said co-author Aidan McConnell, who carried out this research during his master’s degree at the Cavendish Laboratory in Cambridge, and is now a PhD student at ETH, Zürich. “Let’s say sending gifts is inexpensive and we can send numerous parcels on day one. On day two we know which gift we should have sent. By the time the parcels arrive on day three, one out of every four gifts will be correct, and we select these by telling the recipient which deliveries to throw away.”
“That we need to use a filter to make our experiment work is actually pretty reassuring,” said Arvidsson-Shukur. “The world would be very strange if our time-travel simulation worked every time. Relativity and all the theories that we are building our understanding of our universe on would be out of the window.
“We are not proposing a time travel machine, but rather a deep dive into the fundamentals of quantum mechanics. These simulations do not allow you to go back and alter your past, but they do allow you to create a better tomorrow by fixing yesterday’s problems today.”
Resonant enhancement of photo-induced superconductivity in K3C60
by E. Rowe, B. Yuan, M. Buzzi, G. Jotzu, Y. Zhu, M. Fechner, M. Först, B. Liu, D. Pontiroli, M. Riccò, A. Cavalleri in Nature Physics
Researchers at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg, Germany, have long been exploring the effect of using tailored laser drives to manipulate the properties of quantum materials away from equilibrium. One of the most striking demonstrations of these physics has been in unconventional superconductors, where signatures of enhanced electronic coherences and super-transport have been documented in the resulting non-equilibrium states. However, these phenomena have not yet been systematically studied or optimized, primarily due to the complexity of the experiments. Technological applications are therefore still far removed from reality.
In a recent experiment, this same group of researchers discovered a far more efficient way to create a previously observed metastable, superconducting-like state in K3C60 using laser light. The researchers showed that, when tuning the laser light to a specific low frequency resonance, far less powerful light pulses could induce the same effect at much higher temperatures. Laser technology developed at the Institute was key to this work. By tuning the light source to 10 THz, a lower frequency than previously possible, the team successfully recreated the long-lived superconducting-like state in the fullerene-based material while reducing the pulse intensity by a factor of 100. This light-induced state was directly observed to persist at room temperature for 100 picoseconds, but is predicted to have a lifetime of at least 0.5 nanoseconds (a nanosecond is a billionth of a second, a picosecond a trillionth).
Their findings shed new light on the underlying microscopic mechanism in photo-induced superconductivity, says lead author Edward Rowe, a PhD student in the Cavalleri group: “The identification of the resonance frequency will allow theorists to understand which excitations are actually important, since there is currently no widely accepted theoretical explanation of this effect in K3C60.”
Rowe envisages that a light source with a higher repetition rate at the 10 THz frequency could help sustain the metastable state for longer: “If we could deliver each new pulse before the sample returns to its non-superconducting equilibrium state, it may be possible to sustain the superconducting-like state continuously.”
“These experiments are a very nice demonstration of how suitable advances in technology can make applicable many phenomena that are so far not practical,” says MPSD Director Andrea Cavalleri, who sees a two-decade long effort in exploring these effects converging towards future technologies. “It is also clear that a crucial bottleneck to be addressed is the type and availability of laser sources, which should go hand in hand with these studies to bring the field forward.”
Molecular Ion Desorption from LiF(110) Surfaces by Positron Annihilation
by T. Tachibana, D. Hoshi, Y. Nagashima in Physical Review Letters
Positron, the antiparticle of electron, has the same mass and charge as that of an electron but with the sign flipped for the charge. It is an attractive particle for scientists because the use of positrons has led to important insights and developments in the fields of elementary particle physics, atomic physics, materials science, astrophysics, and medicine. For instance, positrons are known to be components of antimatter. They are also powerful in detecting lattice defects in solids and semiconductors and in structural analysis of the topmost surface of crystals. Positronic compounds, namely bound states of positrons with regular atoms, molecules, or ions, represent an intriguing aspect of positron-matter interactions and have been studied experimentally via observation of positron annihilation in gases. It may be possible to generate new molecules and ions via the formation of positron compounds, but no research has ever been done from such a perspective.
Against this backdrop, a research team including Professor Yasuyuki Nagashima from Tokyo University of Science (TUS), Japan, has recently found an innovative way to explore the interactions between positrons and ionic crystals. Their work involved collaborative efforts from Dr. Takayuki Tachibana, former Assistant Professor at TUS and currently affiliated with Rikkyo University, and Mr. Daiki Hoshi, a former graduate student at TUS.
The researchers used a technique based on a well-explored phenomenon arising from the bombardment of a solid with an electron beam. “It has long been known that when electrons are injected into a solid surface, atoms that make up the surface are ejected as monoatomic positive ions,” explains Dr. Tachibana. This process, known as electron-stimulated desorption, motivated the team to explore what would happen if a crystal was instead bombarded with positrons.
In their experiments, the researchers shot either a positron or electron beam at the (110) surface of a lithium fluoride (LiF) crystal. Using carefully placed electric fields generated by deflectors, they controlled the incident energies of the charged particles. Moreover, the deflectors enabled them to redirect any ions desorbed from the crystal towards an ion detector. The detected signals were then used to conduct spectroscopic analysis to identify the precise composition of the desorbed ions.
They found that when the LiF crystal was irradiated with electrons, only the expected monoatomic ions, namely Li+, F+, and H+ (due to residual gases in the experimental chamber) were detected. However, injecting the crystal with positrons led to the detection of positive molecular fluorine ions (F2+) and positive hydrogen fluoride ions (FH+). Notably, this is the first-ever report of molecular ions being ejected upon positron irradiation.
After further analysis and experimentation, the researchers developed a desorption model to explain their observations. According to this model, as positrons are injected into a solid, some of them return to the surface after losing their energy. In the case of LiF crystals, these positrons may attract two neighboring fluorine negative ions on the surface to form a positronic compound. If the bound positron annihilates with one of the fluorine ion’s core electrons, a special type of electron, known as an Auger electron, is emitted, resulting in a charge swap and the generation of a positive F2+ molecular ion. This ion is pushed out of the crystal by the repulsing forces of the nearby Li+ ions. The findings of this study could further our understanding of matter-antimatter interactions.
“The stability and binding properties of positronic compounds provide unique perspectives on the interaction of antiparticles with ordinary substances, paving the way for novel investigations in the field of quantum chemistry,” remarks Dr. Tachibana. “The proposed method could thus pave the way for the generation of new molecular ions and molecules in the future.”
Notably, the approach could be leveraged in many applied fields. In materials science, it could be used to modify the surface of materials and study their properties with unprecedented precision. Other potential applications include cancer therapy, quantum computing, energy storage, and next-generation electronic devices.
Machine learning the dimension of a Fano variety
by Tom Coates, Alexander M. Kasprzyk, Sara Veneziale in Nature Communications
Applying machine learning to find the properties of atomic pieces of geometry shows how AI has the power to accelerate discoveries in maths.
Mathematicians from Imperial College London and the University of Nottingham have, for the first time, used machine learning to expand and accelerate work identifying ‘atomic shapes’ that form the basic pieces of geometry in higher dimensions.
The way they used artificial intelligence, in the form of machine learning, could transform how maths is done, say the authors. Dr Alexander Kasprzyk from the University of Nottingham said: “For mathematicians, the key step is working out what the pattern is in a given problem. This can be very difficult, and some mathematical theories can take years to discover.”
Professor Tom Coates, from the Department of Mathematics at Imperial, added: “We have shown that machine learning can help uncover patterns within mathematical data, giving us both new insights and hints of how they can be proved.”
PhD student Sara Veneziale, from the Department of Mathematics at Imperial, said: “This could be very broadly applicable, such that it could rapidly accelerate the pace at which maths discoveries are made. It’s like when computers were first used in maths research, or even calculators: it’s a step-change in the way we do maths.”
Mathematicians describe shapes using equations, and by analysing these equations can break the shape down into fundamental pieces. These are the building blocks of shapes, the equivalent of atoms, and are called Fano varieties.
The Imperial and Nottingham team began building a ‘periodic table’ of these Fano varieties several years ago, but finding ways of classifying them into groups with common properties has been challenging. Now, they have used machine learning to reveal unexpected patterns in the Fano varieties.
One aspect of a Fano variety is its quantum period — a sequence of numbers that acts like a barcode or fingerprint. It has been suggested that the quantum period defines the dimension of the Fano variety, but there has been no theoretical proposal for how this works, so no way to test it on the huge set of known Fano varieties. Machine learning, however, is built to find patterns in large datasets. By training a machine learning model with some example data, the team were able to show the resulting model could predict the dimensions of Fano varieties from quantum periods with 99% accuracy.
The AI model doesn’t conclusively show the team have discovered a new statement, so they then used more traditional mathematical methods to prove that the quantum period defines the dimension — using the AI model to guide them.
As well as using machine learning to discover new maths, the team say that the datasets used in maths could help refine machine learning models. Most models are trained on data taken from real life, such as health or transport data, which are inherently ‘noisy’ — they contain a lot of randomness that to some degree mask the real information.
Mathematical data is ‘pure’ — noise free — and contains patterns and structures that underly the data, waiting to be uncovered. This data can therefore be used as testing grounds for machine learning models, improving their ability to find new patterns.
A quantum engine in the BEC–BCS crossover
by Jennifer Koch, Keerthy Menon, Eloisa Cuestas, Sian Barbosa, Eric Lutz, Thomás Fogarty, Thomas Busch, Artur Widera in Nature
Quantum mechanics is a branch of physics that explores the properties and interactions of iparticles at very small scale, such as atoms and molecules. This has led to the development of new technologies that are more powerful and efficient compared to their conventional counterparts, causing breakthroughs in areas such as computing, communication, and energy.
At the Okinawa Institute of Science and Technology (OIST), researchers at the Quantum Systems Unit have collaborated with scientists from the University of Kaiserslautern-Landau and the University of Stuttgart to design and build an engine that is based on the special rules that particles obey at very small scales. They have developed an engine that uses the principles of quantum mechanics to create power, instead of the usual way of burning fuel. The paper describing these results is co-authored by OIST researchers Keerthy Menon, Dr. Eloisa Cuestas, Dr. Thomas Fogarty and Prof.
In a classical car engine, usually a mixture of fuel and air is ignited inside a chamber. The resulting explosion heats the gas in the chamber, which in turn pushes a piston in and out, producing work that turns the wheels of the car.
In their quantum engine the scientists have replaced the use of heat with a change in the quantum nature of the particles in the gas. To understand how this change can power the engine, we need to know that all particles in nature can be classified as either bosons or fermions, based on their special quantum characteristics.
At very low temperatures, where quantum effects become important, bosons have a lower energy state than fermions, and this energy difference can be used to power an engine. Instead of heating and cooling a gas cyclically like a classical engine does, the quantum engine works by changing bosons into fermions and back again.
“To turn fermions into bosons, you can take two fermions and combine them into a molecule. This new molecule is a boson. Breaking it up allows us to retrieve the fermions again. By doing this cyclically, we can power the engine without using heat,” Prof. Thomas Busch, leader of the Quantum Systems Unit explained.
While this type of engine only works in the quantum regime, the team found that its efficiency is quite high and can reach up to 25% with the present experimental set up built by the collaborators in Germany.
This new engine is an exciting development in the field of quantum mechanics and has the potential to lead to further advances in the burgeoning area of quantum technologies. But does this mean we will soon see quantum mechanics powering the engines of our cars?
“While these systems can be highly efficient, we have only done a proof-of-concept together with our experimental collaborators,” explained Keerthy Menon. “There are still many challenges in building a useful quantum engine.”
Heat can destroy the quantum effects if the temperature gets too high, so researchers must keep their system as cold as possible. However, this requires a substantial amount of energy to run the experiment at these low temperatures in order to protect the sensitive quantum state.
The next steps in the research will involve addressing fundamental theoretical questions about the system’s operation, optimizing its performance, and investigating its potential applicability to other commonly used devices, such as batteries and sensors.
Observation of the effect of gravity on the motion of antimatter
by E. K. Anderson, C. J. Baker, W. Bertsche, N. M. Bhatt, et al in Nature
If you dropped antimatter, would it fall down or up? In a unique laboratory experiment, researchers have now observed the downward path taken by individual atoms of antihydrogen, providing a definitive answer: antimatter falls down.
In confirming antimatter and regular matter are gravitationally attracted, the finding also rules out gravitational repulsion as the reason why antimatter is largely missing from the observable universe.
Researchers from the international Antihydrogen Laser Physics Apparatus (ALPHA) collaboration at CERN in Switzerland published their findings, an effort supported by more than a dozen countries and private institutions, including the U.S. through the joint U.S. National Science Foundation/Department of Energy Partnership in Basic Plasma Science and Engineering program.
“The success of the ALPHA collaboration is a testament to the importance of teamwork across continents and scientific communities,” says Vyacheslav “Slava” Lukin, a program director in NSF’s Physics Division. “Understanding the nature of antimatter can help us not only understand how our universe came to be but can enable new innovations never before thought possible — like positron emission tomography (PET) scans that have saved many lives by applying our knowledge of antimatter to detect cancerous tumors in the body.”
Beyond the imagined antimatter-fueled warp drives and photon torpedoes of Star Trek, antimatter is completely real, yet mysteriously scarce.
“Einstein’s theory of general relativity says antimatter should behave exactly the same as matter,” said University of California, Berkeley plasma physicist and ALPHA collaboration member Jonathan Wurtele. “Many indirect measurements indicate that gravity interacts with antimatter as expected” he added, “but until the result today, nobody had actually performed a direct observation that could rule out, for example, antihydrogen moving upwards as opposed to downwards in a gravitational field.”
Our bodies, the Earth, and most everything else scientists know about in the universe are overwhelmingly made of regular matter consisting of protons, neutrons, and electrons, like atoms of oxygen, carbon, iron and the other elements of the periodic table.
Antimatter, on the other hand, is regular matter’s twin, though with some opposite properties. For example, antiprotons have a negative charge while protons have a positive charge. Antielectrons (also known as positrons) are positive while electrons are negative. However, perhaps most challenging for experimenters, “As soon as antimatter touches matter, it blows up,” said ALPHA collaboration member and University of California, Berkeley plasma physicist Joel Fajans.
The combined mass of matter and antimatter is transformed entirely into energy in a reaction so powerful that scientists call it an annihilation.
“For a given mass, such annihilations are the densest form of energy release that we know of,” Fajans added.
But, the amount of antimatter used in the ALPHA experiment is so small that the energy created by antimatter/matter annihilations is perceptible only to sensitive detectors.
“Still, we have to manipulate the antimatter very carefully or we will lose it,” said Fajans.
“Broadly speaking, we’re making antimatter and we’re doing a Leaning Tower of Pisa kind of experiment,” said Wurtele, referring to their experiment’s simpler intellectual ancestor, Galileo’s perhaps apocryphal 16th century experiment demonstrating identical gravitational acceleration of two simultaneously dropped objects of similar volume but different mass. “We’re letting the antimatter go, and we’re seeing if it goes up or down.”
For the ALPHA experiment, the antihydrogen was contained within a tall cylindrical vacuum chamber with a variable magnetic trap, called ALPHA-g. The scientists reduced the strength of the trap’s top and bottom magnetic fields until the antihydrogen atoms could escape and the relatively weak influence of gravity became apparent. As each antihydrogen atom escaped the magnetic trap, it touched the chamber walls either above or below the trap and annihilated, which the scientists could detect and count.
The researchers repeated the experiment more than a dozen times, varying the magnetic field strength at the top and bottom of the trap to rule out possible errors. They observed that when the weakened magnetic fields were precisely balanced at the top and bottom, about 80% of the antihydrogen atoms annihilated beneath the trap — a result consistent with how a cloud of regular hydrogen would behave under the same conditions. Thus, gravity was causing the antihydrogen to fall down.
Despite some modest sources of antimatter — like positrons emitted from the decay of potassium, even within a banana — scientists do not see much of it in the universe. However, the laws of physics predict antimatter should exist in roughly equal amounts as regular matter. Scientists call that conundrum the baryogenesis problem. One potential explanation is that antimatter was gravitationally repelled by regular matter during the big bang, although the new findings suggest that theory no longer seems plausible.
“We’ve ruled out antimatter being repelled by the gravitational force as opposed to attracted,” said Wurtele. That doesn’t mean there isn’t a difference in the gravitational force on antimatter, he adds. Only a more precise measurement will tell.
The ALPHA collaboration researchers will continue to probe the nature of antihydrogen. In addition to refining their measurement of the effect of gravity, they are also studying how antihydrogen interacts with electromagnetic radiation through spectroscopy.
“If antihydrogen were somehow different from hydrogen, that would be a revolutionary thing because the physical laws, both in quantum mechanics and gravity, say the behavior should be the same,” said Wurtele. “However, one doesn’t know until one does the experiment.”
Extreme thermodynamics in nanolitre volumes through stimulated Brillouin–Mandelstam scattering
by Andreas Geilen, Alexandra Popp, Debayan Das, Saher Junaid, Christopher G. Poulton, Mario Chemnitz, Christoph Marquardt, Markus A. Schmidt, Birgit Stiller in Nature Physics
Negative pressure is a rare and challenging-to-detect phenomenon in physics. Using liquid-filled optical fibers and sound waves, researchers at the Max Planck Institute for the Science of Light (MPL) in Erlangen have now discovered a new method to measure it. In collaboration with the Leibniz Institute of Photonic Technologies in Jena (IPHT), the scientists in the Quantum Optoacoustics research group, led by Birgit Stiller, can gain important insights into thermodynamic states.
As a physical quantity pressure is encountered in various fields: atmospheric pressure in meteorology, blood pressure in medicine, or even in everyday life with pressure cookers and vacuum-sealed foods. Pressure is defined as a force per unit area acting perpendicular to a surface of a solid, liquid, or gas. Depending on the direction in which the force acts within a closed system, very high pressure can lead to explosive reactions in extrem cases, while very low pressure in a closed system can cause the implosion of the system itself. Overpressure always means that the gas or liquid pushes against the walls of its container from the inside, like a balloon expanding when more air is added. Regardless of whether it’s high or low pressure, the numerical value of pressure is always positive under normal circumstances.
However, liquids exhibit a peculiar characteristic. They can exist in a specific metastable state corresponding to a negative pressure value. In this metastable state, even a tiny external influence can cause the system to collapse into one state or another. One can imagine it as sitting at the top of a roller coaster: the slightest touch on one side or the other sends you hurtling down the tracks. In their current research, the scientists are examining the metastable state of liquids with negative pressure. To achieve this, the research team combined two unique techniques in a study to measure various thermodynamic states. Initially, tiny amounts — nanoliters — of a liquid were encapsulated in a fully closed optical fiber, allowing both highly positive and negative pressures. Subsequently, the specific interaction of optical and acoustic waves in the liquid enabled the sensitive measurement of the influence of pressure and temperature in different states of the liquid. Sound waves act as sensors for examining negative pressure values, exploring this unique state of matter with high precision and detailed spatial resolution.
The influence of negative pressure on a liquid can be envisioned as follows: According to the laws of thermodynamics, the volume of the liquid will decrease, but the liquid is retained in the glass fiber capillary by adhesive forces, much like a water droplet sticking to a finger. This results in a “stretching” of the liquid. It is pulled apart and behaves like a rubber band being stretched. Measuring this exotic state typically requires complex equipment with heightened safety precautions. High pressures can be hazardous endeavors, particularly with toxic liquids. Carbon disulfide, used by the researchers in this study, falls into this category. Due to this complication, previous measurement setups for generating and determining negative pressures have required significant laboratory space and even posed a disturbance to the system in the metastable state. With the method presented here, the researchers have instead developed a tiny, simple setup in which they can make very precise pressure measurements using light and sound waves. The fiber used for this purpose is only as thick as a human hair.
“Some phenomena which are difficult to explore with ordinary and established methods can become unexpectedly accessible when new measurement methods are combined with novel platforms. I find that exciting,” says Dr. Birgit Stiller, head of the Quantum Optoacoustics research group at MPL. The sound waves used by the group can detect temperature, pressure, and strain changes very sensitively along an optical fiber. Furthermore, spatially resolved measurements are possible, meaning that the sound waves can provide an image of the situation inside the optical fiber at centimeter-scale resolution along its length. “Our method allows us to gain a deeper understanding of the thermodynamic dependencies in this unique fiber-based system,” says Alexandra Popp, one of the two lead authors of the article. The other lead author, Andreas Geilen, adds: “The measurements revealed some surprising effects. The observation of the negative pressure regime becomes abundantly clear when looking at the frequency of the sound waves.”
The combination of optoacoustic measurements with tightly sealed capillary fibers enables new discoveries regarding the monitoring of chemical reactions in toxic liquids within otherwise difficult-to-investigate materials and microreactors. It can penetrate new, hard-to-access areas of thermodynamics. “This new platform of fully sealed liquid core fibers provides access to high pressures and other thermodynamic regimes,” says Prof. Markus Schmidt from IPHT in Jena, and Dr. Mario Chemnitz, also from IPHT in Jena, emphasizes: “It is of great interest to investigate and even tailor further nonlinear optical phenomena in this type of fiber.” These phenomena can unlock previously unexplored and potentially new properties in the unique thermodynamic state of materials.
Birgit Stiller concludes: “The collaboration between our research groups in Erlangen and Jena, with their respective expertise, is unique in gaining new insights into thermodynamic processes and regimes on a tiny and easy-to-handle optical platform.”
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