Physics News and Discussions

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Strange new phase of matter created in quantum computer acts like it has two time dimensions
https://phys.org/news/2022-07-strange-p ... sions.html
by Simons Foundation

By shining a laser pulse sequence inspired by the Fibonacci numbers at atoms inside a quantum computer, physicists have created a remarkable, never-before-seen phase of matter. The phase has the benefits of two time dimensions despite there still being only one singular flow of time, the physicists report July 20 in Nature.

This mind-bending property offers a sought-after benefit: Information stored in the phase is far more protected against errors than with alternative setups currently used in quantum computers. As a result, the information can exist without getting garbled for much longer, an important milestone for making quantum computing viable, says study lead author Philipp Dumitrescu.

The approach's use of an "extra" time dimension "is a completely different way of thinking about phases of matter," says Dumitrescu, who worked on the project as a research fellow at the Flatiron Institute's Center for Computational Quantum Physics in New York City. "I've been working on these theory ideas for over five years, and seeing them come actually to be realized in experiments is exciting."

Dumitrescu spearheaded the study's theoretical component with Andrew Potter of the University of British Columbia in Vancouver, Romain Vasseur of the University of Massachusetts, Amherst, and Ajesh Kumar of the University of Texas at Austin. The experiments were carried out on a quantum computer at Quantinuum in Broomfield, Colorado, by a team led by Brian Neyenhuis.

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Physicists find signatures of highly entangled quantum matter
https://phys.org/news/2022-07-physicist ... antum.html
by The University of Hong Kong

Via large-scale simulations on supercomputers, a research team from the Department of Physics, the University of Hong Kong (HKU), discovered clear evidence to characterize a highly entangled quantum matter phase—the quantum spin liquid (QSL), a phase of matter that remains disordered even at very low temperatures. This research has recently been published in npj Quantum Materials.

QSLs were proposed in 1973 by P. W. Anderson, the Nobel Physics Laureate of 1977. They have the potential to be used in topological quantum computing and to help understand the mechanisms of high-temperature superconductors that could greatly reduce energy costs during electricity transport owing to the absence of electrical resistance.

The QSL is called a liquid due to its lack of conventional order. QSLs have a topological order that originates from long-range and strong quantum entanglement. The detection of this topological order is a tough task due to the lack of materials that can perfectly achieve the many model systems that scientists propose to find a topological order of QSL and prove its existence. Thus, there has not been firmly accepted concrete evidence showing QSLs exist in nature.

Jiarui Zhao, Dr. Bin-Bin Chen, Dr. Zheng Yan, and Dr. Zi Yang Meng from HKU Department of Physics successfully probed this topological order in a phase of the Kagome lattice quantum spin model, which is a two-dimensional lattice model with intrinsic quantum entanglement and proposed by scientists that have Z2 (a cyclic group of order 2) topological order, via a carefully designed numerical experiment on supercomputers. Their unambiguous results of topological entanglement entropy strongly suggest the existence of QSLs in high entanglement quantum models from a numerical perspective.

"Our work takes advantage of the superior computing power of modern supercomputers, and we use them to simulate a very complicated model which is thought to possess topological order. With our findings, physicists are more confident that QSLs should exist in nature," said Jiarui Zhao, the first author of the journal paper and a Ph.D. student at the Department of Physics.

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Study shows that skyrmions and antiskyrmions can coexist at different temperatures
https://phys.org/news/2022-07-skyrmions ... tures.html
by Ingrid Fadelli , Phys.org

Matching particles and antiparticles are small units of matter that have the same mass but opposite electric charges. Typically, these units of matter with opposite electric charge tend to annihilate one another.

Studies have predicted that the same behavior should also be observed in magnetic solitons with opposing topological charges. Magnetic solitons, or solitary waves, are localized spin textures that maintain their shape while propagating at a constant velocity and can be distinguished by their topological charge Q.

Based on theoretical predictions, magnetic solitons with opposite Q values should continuously merge and annihilate themselves. This includes skyrmions and antiskyrmions, swirling topological magnetic textures that are realized as emergent particles in magnets.

Researchers at Forschungszentrum Jülich and JARA in Germany have recently carried out one of the first experiments aimed at testing these predictions. Their paper, published in Nature Physics, demonstrates the creation and annihilation of skyrmion-antiskyrmion pairs in a cubic chiral magnet.

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Simulating infinitely many chaotic particles using a quantum computer
https://phys.org/news/2022-08-simulatin ... antum.html
by Bob Yirka , Phys.org

A team of researchers at Quantinuum, working with a colleague at the University of Texas, Austin, has developed a way to simulate infinitely many chaotic particles using a quantum computer running with a limited number of qubits. In their paper published in the journal Nature Physics, the group describes their technique.

To learn more about how molecules behave in materials, researchers have come up with strategies to simulate their behavior on a computer. Such attempts have worked well with simple operations but have run into trouble when simulating complexity, such as an infinitely long line of interacting particles over a given period of time. Attempts on traditional supercomputers have bogged down, and researchers have theorized that a quantum computer could do the job quite nicely. In this new effort, the researchers have found that is indeed the case.

The researchers claim the key to running an algorithm capable of tackling such a problem came down to a design that not only carried out the operations needed to run the simulation but also to add code that would allow such a simulation to run with very few qubits. Once they had an algorithm that they thought would work, the team turned to the hardware. They chose a machine using qubits represented by ytterbium atoms—and they altered the number of qubits that were run from three to 11.

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Manipulating interlayer magnetic coupling in van der Waals heterostructures
https://phys.org/news/2022-08-interlaye ... n-der.html
by FLEET

An RMIT-led international collaboration has observed, for the first time, electric gate-controlled exchange-bias effect in van der Waals (vdW) heterostructures, offering a promising platform for future energy-efficient, beyond-CMOS electronics.

The exchange-bias (EB) effect, which originates from interlayer magnetic coupling, has played a significant role in fundamental magnetics and spintronics since its discovery.

Although manipulating the EB effect by an electronic gate has been a significant goal in spintronics, until now, only very limited electrically-tunable EB effects have been demonstrated.

Electrical gate-manipulated EB effects in AFM-FM structures enable scalable energy-efficient spin-orbit logic, which is very promising for beyond-COMS devices in future low-energy electronic technologies.

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A Step Towards Quantum Gravity
August 12, 2022

Entire Article:

(EurekAlert) In Einstein’s theory of general relativity, gravity arises when a massive object distorts the fabric of spacetime the way a ball sinks into a piece of stretched cloth. Solving Einstein’s equations by using quantities that apply across all space and time coordinates could enable physicists to eventually find their ‘white whale’: a quantum theory of gravity. In a new article in EPJ Historical Perspectives on Contemporary Physics, Donald Salisbury from Austin College in Sherman, USA, explains how Peter Bergmann and Arthur Komar first proposed a way to get one step closer to this goal by using Hamilton-Jacobi techniques. These arose in the study of particle motion in order to obtain the complete set of solutions from a single function of particle position and constants of the motion.

Three of the four fundamental forces – strong, weak, and electromagnetic – hold under both the ordinary world of our everyday experience, modelled by classical physics, and the spooky world of quantum physics. Problems arise, though, when trying to apply to the fourth force, gravity, to the quantum world. In the 1960s and 1970s, Peter Bergmann of Syracuse University, New York and his associates recognised that in order to someday reconcile Einstein’s theory of general relativity with the quantum world, they needed to find quantities for determining events in space and time that applied across all frames of reference. They succeeded in doing this by using the Hamilton-Jacobi techniques.

This is in contrast to other researchers’ approaches, including that of John Wheeler and Bryce DeWitt, who thought it only essential to find quantities of space that applied across all frames of reference. By excluding time, their solutions result in ambiguities in the way time develops, which are known as the problem of time.

Salisbury concludes that because the approach taken by Bergmann and associates resolves the ambiguity in the way time develops, their approach deserves more recognition by those exploring an eventual theory of quantum gravity.

Source: https://www.eurekalert.org/news-releases/961729

For the truly interested, you can go to this site, read an abstract of the referenced article and buy a PDF copy of the full article for $39.95: https://link.springer.com/article/10.1 ... 2-00039-8

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Matter at extreme conditions of very high temperature and pressure turns out to be remarkably simple and universal

by Queen Mary, University of London
https://phys.org/news/2022-08-extreme-c ... ssure.html

Scientists at Queen Mary University of London have made two discoveries about the behavior of "supercritical matter"—matter at the critical point where the differences between liquids and gases seemingly disappear.

While the behavior of matter at reasonably low temperature and pressure was well understood, the picture of matter at high temperature and pressure was blurred. Above the critical point, differences between liquids and gases seemingly disappear, and the supercritical matter was thought to become hot, dense and homogeneous.

The researchers believed there was new physics yet to be uncovered about this matter at the supercritical state.

By applying two parameters—the heat capacity and the length over which waves can propagate in the system, they made two key discoveries. First, they found that there is a fixed inversion point between the two where matter changes its physical properties—from liquid-like to gas-like. They also found that this inversion point is remarkably close in all systems studied, telling us that the supercritical matter is intriguingly simple and amenable to new understanding.

As well as fundamental understanding of the states of matter and the phase transition diagram, understanding supercritical matter has many practical applications; hydrogen and helium are supercritical in gas giant planets such as Jupiter and Saturn, and therefore govern their physical properties. In green environmental applications, supercritical fluids have also proved to be very efficient at destroying hazardous wastes, but engineers increasingly want guidance from theory in order to improve efficiency of supercritical processes.

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2D array of electron and nuclear spin qubits opens new frontier in quantum science
https://phys.org/news/2022-08-2d-array- ... ubits.html
by Purdue University

By using photons and electron spin qubits to control nuclear spins in a two-dimensional material, researchers at Purdue University have opened a new frontier in quantum science and technology, enabling applications like atomic-scale nuclear magnetic resonance spectroscopy, and to read and write quantum information with nuclear spins in 2D materials.

As published Monday (Aug. 15) in Nature Materials, the research team used electron spin qubits as atomic-scale sensors, and also to effect the first experimental control of nuclear spin qubits in ultrathin hexagonal boron nitride.

"This is the first work showing optical initialization and coherent control of nuclear spins in 2D materials," said corresponding author Tongcang Li, a Purdue associate professor of physics and astronomy and electrical and computer engineering, and member of the Purdue Quantum Science and Engineering Institute.

"Now we can use light to initialize nuclear spins and with that control, we can write and read quantum information with nuclear spins in 2D materials. This method can have many different applications in quantum memory, quantum sensing, and quantum simulation."

Quantum technology depends on the qubit, which is the quantum version of a classical computer bit. It is often built with an atom, subatomic particle, or photon instead of a silicon transistor. In an electron or nuclear spin qubit, the familiar binary "0" or "1" state of a classical computer bit is represented by spin, a property that is loosely analogous to magnetic polarity—meaning the spin is sensitive to an electromagnetic field. To perform any task, the spin must first be controlled and coherent, or durable.

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New quantum technology combines free electrons and photons
https://phys.org/news/2022-08-quantum-t ... trons.html
by Max Planck Society

Faster computers, tap-proof communication, better car sensors—quantum technologies have the potential to revolutionize our lives just as the invention of computers or the internet once did. Experts worldwide are trying to implement findings from basic research into quantum technologies. To this end, they often require individual particles, such as photons—the elementary particles of light—with tailored properties.

However, obtaining individual particles is complicated and requires intricate methods. In a study recently published in the journal Science, researchers now present a new method that simultaneously generates two individual particles in form of a pair.

Fundamental quantum physics in electron microscopes

The international team from the Göttingen Max Planck Institute (MPI) for Multidisciplinary Sciences, the University of Göttingen, and the Swiss Federal Institute of Technology in Lausanne (EPFL) succeeded in coupling single free electrons and photons in an electron microscope. In the Göttingen experiment, the beam from an electron microscope passes through an integrated optical chip, fabricated by the Swiss team. The chip consists of a fiber-optic coupling and a ring-shaped resonator that stores light by keeping moving photons on a circular path.

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New evidence that water separates into two different liquids at low temperatures
https://phys.org/news/2022-08-evidence- ... tures.html
by University of Birmingham

A new kind of "phase transition" in water was first proposed 30 years ago in a study by researchers from Boston University. Because the transition has been predicted to occur at supercooled conditions, however, confirming its existence has been a challenge. That's because at these low temperatures, water really does not want to be a liquid, instead it wants to rapidly become ice. Because of its hidden status, much is still unknown about this liquid-liquid phase transition, unlike the everyday examples of phase transitions in water between a solid or vapor phase and a liquid phase.

This new evidence, published in Nature Physics, represents a significant step forward in confirming the idea of a liquid-liquid phase transition first proposed in 1992. Francesco Sciortino, now a professor at Sapienza Università di Roma, was a member of the original research team at Boston University and is also a co-author of this paper.

The team has used computer simulations to help explain what features distinguish the two liquids at the microscopic level. They found that the water molecules in the high-density liquid form arrangements that are considered to be "topologically complex," such as a trefoil knot (think of the molecules arranged in such a way that they resemble a pretzel) or a Hopf link (think of two links in a steel chain). The molecules in the high-density liquid are thus said to be entangled.

In contrast, the molecules in the low-density liquid mostly form simple rings, and hence the molecules in the low-density liquid are unentangled.

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Surprising attractiveness of hurdle to developing safe, clean and carbon-free energy
https://phys.org/news/2022-08-hurdle-sa ... nergy.html
by John Greenwald

Scientists have discovered the remarkable impact of reversing a standard method for combatting a key obstacle to producing fusion energy on Earth. Theorists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have proposed doing precisely the opposite of the prescribed procedure to sharply improve future results.

Tearing holes in plasma

The problem, called "locked tearing modes," occurs in all today's tokamaks, doughnut-shaped magnetic facilities designed to create and control the virtually unlimited fusion power that drives the sun and stars. The instability-caused modes rotate with the hot, charged plasma— the fourth state of matter composed of free electrons and atomic nuclei that fuels fusion reaction

s—and tear holes called islands in the magnetic field that confines the gas, allowing the leakage of key heat.

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Scientists identify liquid-like atoms in densely packed solid glasses
https://phys.org/news/2022-08-scientist ... solid.html
by Zhang Nannan, Chinese Academy of Sciences

Metallic glass is an important advanced alloy, holding promise for broad engineering applications. It appears as a solid form in many aspects, with beautiful metal appearance, exceeding elasticity, high strength, and a densely packed atomic structure.

However, this all-solid notion has now been challenged. Prof. Bai Haiyang from the Institute of Physics of the Chinese Academy of Sciences (CAS) has recently shown the existence of liquid-like atoms in metallic glasses. These atoms inherit the dynamics of high-temperature liquid atoms, revealing the nature of metallic glasses as part-solid and part-liquid.

Results were published in Nature Materials.

Condensed matter can generally be classified into solid and liquid states. Under extreme conditions or in specific systems, matter exists in special states that simultaneously exhibit some properties of both solids and liquids. In this case, solids may contain rapidly diffusing, liquid-like atoms that can move fast even at low temperatures.

For example, ice enters a "superionic" state under high pressure at high temperatures. In this state, H atoms can diffuse freely while O atoms are fixed in their sublattices. Such special states are also observed in Earth's inner core and in the Li-conducting materials of advanced batteries, which are drawing growing attention in science and engineering.

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Physicists entangle more than a dozen photons efficiently
https://phys.org/news/2022-08-physicist ... ently.html
by Max Planck Society MPQ

Physicists at the Max Planck Institute of Quantum Optics have managed to entangle more than a dozen photons efficiently and in a defined way. They are thus creating a basis for a new type of quantum computer. Their study is published in Nature.

The phenomena of the quantum world, which often seem bizarre from the perspective of the common everyday world, have long since found their way into technology. For example, entanglement: a quantum-physical connection between particles that links them in a strange way over arbitrarily long distances. It can be used, for example, in a quantum computer—a computing machine that, unlike a conventional computer, can perform numerous mathematical operations simultaneously. However, in order to use a quantum computer profitably, a large number of entangled particles must work together. They are the basic elements for calculations, so-called qubits.

"Photons, the particles of light, are particularly well suited for this because they are robust by nature and easy to manipulate," says Philip Thomas, a doctoral student at the Max Planck Institute of Quantum Optics (MPQ) in Garching near Munich. Together with colleagues from the Quantum Dynamics Division led by Prof. Gerhard Rempe, he has now succeeded in taking an important step towards making photons usable for technological applications such as quantum computing: For the first time, the team generated up to 14 entangled photons in a defined way and with high efficiency.

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Physicists develop a perfect light trap
https://phys.org/news/2022-08-physicists.html
by Vienna University of Technology

Whether in photosynthesis or in a photovoltaic system: if you want to use light efficiently, you have to absorb it as completely as possible. However, this is difficult if the absorption is to take place in a thin layer of material that normally lets a large part of the light pass through.

Now, research teams from TU Wien and from The Hebrew University of Jerusalem have found a surprising trick that allows a beam of light to be completely absorbed even in the thinnest of layers: They built a "light trap" around the thin layer using mirrors and lenses, in which the light beam is steered in a circle and then superimposed on itself—exactly in such a way that the beam of light blocks itself and can no longer leave the system. Thus, the light has no choice but to be absorbed by the thin layer—there is no other way out.

This absorption-amplification method, which has now been presented in the scientific journal Science, is the result of a fruitful collaboration between the two teams: the approach was suggested by Prof. Ori Katz from The Hebrew University of Jerusalem and conceptualized with Prof. Stefan Rotter from TU Wien; the experiment was carried out in by the lab team in Jerusalem and the theoretical calculations came from the team in Vienna.

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Extended tests with levitated force sensor fail to find evidence of fifth force
https://phys.org/news/2022-08-levitated ... dence.html
by Bob Yirka , Phys.org

A team of researchers from Nanjing University, working with two colleagues from the University of Science and Technology of China, has conducted new tests of the chameleon theory and report a failure to find any evidence of a fifth force. They have published their paper in the journal Nature Physics.

Prior research has suggested that there is a mysterious force acting on the universe—dubbed by theoretical physicists as dark energy, it was theorized as a way to explain why the universe is expanding at an accelerating rate. Despite much effort, no one has been able to prove that dark energy exists. One theory called the chameleon theory suggests that objects affected by gravity can behave in ways that fluctuate based on factors in their environment. The theory includes the idea of a chameleon field as a fifth force. The theory has been hotly debated because it directly contradicts the theory of general relativity, which states that gravitational forces are expected to be constant.

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Researchers use infrared light to wirelessly transmit power over 30 meters
https://phys.org/news/2022-08-infrared- ... eters.html
by Optica

Imagine walking into an airport or grocery store and your smartphone automatically starts charging. This could be a reality one day, thanks to a new wireless laser charging system that overcomes some of the challenges that have hindered previous attempts to develop safe and convenient on-the-go charging systems.

"The ability to power devices wirelessly could eliminate the need to carry around power cables for our phones or tablets," said research team leader Jinyong Ha from Sejong University in South Korea. "It could also power various sensors such as those in Internet of Things (IoT) devices and sensors used for monitoring processes in manufacturing plants."

In Optics Express, the researchers describe their new system, which uses infrared light to safely transfer high levels of power. Laboratory tests showed that it could transfer 400 mW light power over distances of up to 30 meters. This power is sufficient for charging sensors, and with further development, it could be increased to levels necessary to charge mobile devices.

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Less risk, less costs: Portable spectroscopy devices could soon become real
https://phys.org/news/2022-09-portable- ... -real.html
by Petra Giegerich, Universitaet Mainz

Nuclear magnetic resonance (NMR) is an analytical tool with a wide range of applications, including the magnetic resonance imaging that is used for diagnostic purposes in medicine. However, NMR often requires powerful magnetic fields to be generated, which limits the scope of its use.

Researchers working at Johannes Gutenberg University Mainz (JGU) and the Helmholtz Institute Mainz (HIM) have now discovered potential new ways to reduce the size of the corresponding devices and also the possible associated risk by eliminating the need for strong magnetic fields. This is achieved by combining so-called zero- to ultralow-field NMR with a special hyperpolarization technique. "This exciting new method is based on an innovative concept. It opens up a whole range of opportunities and overcomes previous disadvantages," said Dr. Danila Barskiy, a Sofja Kovalevskaja Award winner who has been working in the relevant discipline at JGU and HIM since 2020.

New approach to enable measurements without strong magnetic fields

The current generation of NMR devices is—because of the magnets—extremely heavy and expensive. Another complicating factor is the present shortage of liquid helium that is employed as a coolant. "With our new technique we are gradually moving ZULF NMR towards a status of being completely magnet-free, but we still have many challenges to overcome," stated Barskiy.

To make magnets redundant in this context, Barskiy has come up with the idea of combining zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) with a special technique that makes it possible to hyperpolarize atomic nuclei. ZULF NMR is itself a recently developed form of spectroscopy that provides abundant analytical results without the need for large magnetic fields.

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SU(N) matter is about 3 billion times colder than deep space
https://phys.org/news/2022-09-sun-billi ... space.html
by Rice University

Japanese and U.S. physicists have used atoms about 3 billion times colder than interstellar space to open a portal to an unexplored realm of quantum magnetism.

"Unless an alien civilization is doing experiments like these right now, anytime this experiment is running at Kyoto University it is making the coldest fermions in the universe," said Rice University's Kaden Hazzard, corresponding theory author of a study published today in Nature Physics. "Fermions are not rare particles. They include things like electrons and are one of two types of particles that all matter is made of."

A Kyoto team led by study author Yoshiro Takahashi used lasers to cool its fermions, atoms of ytterbium, within about one-billionth of a degree of absolute zero, the unattainable temperature where all motion stops. That's about 3 billion times colder than interstellar space, which is still warmed by the afterglow from the Big Bang.

"The payoff of getting this cold is that the physics really changes," Hazzard said. "The physics starts to become more quantum mechanical, and it lets you see new phenomena."

Atoms are subject to the laws of quantum dynamics just like electrons and photons, but their quantum behaviors only become evident when they are cooled within a fraction of a degree of absolute zero. Physicists have used laser cooling to study the quantum properties of ultracold atoms for more than a quarter century. Lasers are used to both cool the atoms and restrict their movements to optical lattices, 1D, 2D or 3D channels of light that can serve as quantum simulators capable of solving complex problems beyond the reach of conventional computers.

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Physicists develop a linear response theory for open systems having exceptional points
https://phys.org/news/2022-09-physicist ... ional.html
by Michigan Technological University

Linear analysis plays a central role in science and engineering. Even when dealing with nonlinear systems, understanding the linear response is often crucial for gaining insight into the underlying complex dynamics. In recent years, there has been a great interest in studying open systems that exchange energy with a surrounding reservoir. In particular, it has been demonstrated that open systems whose spectra exhibit non-Hermitian singularities called exceptional points can demonstrate a host of intriguing effects with potential applications in building new lasers and sensors.

At an exceptional point, two or modes become exactly identical. To better understand this, let us consider how drums produce sound. The membrane of the drum is fixed along its perimeter but free to vibrate in the middle.

As a result, the membrane can move in different ways, each of which is called a mode and exhibits a different sound frequency. When two different modes oscillate at the same frequency, they are called degenerate. Exceptional points are very peculiar degeneracies in the sense that not only the frequencies of the modes are identical but also the oscillations themselves. These points can exist only in open, non-Hermitian systems with no analog in closed, Hermitian systems.

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Investigating magnetic excitation-induced spin current in chromium trihalides

by Tokyo Institute of Technology
https://phys.org/news/2022-09-magnetic- ... lides.html

An ingenious approach toward developing low-power, high-speed, and high-density memory devices is based on spintronics, an emerging frontier in technology that harnesses a degree of freedom of electrons known as spin. Put simply, electrons, along with their negative charge, possess a spin whose orientation can be controlled using magnetic fields. This is particularly relevant for magnetic insulators, in which the electrons cannot move around, but the spin remains controllable. In these materials, the magnetic excitations can give rise to a spin current, which forms the basis of spintronics.

Scientists have been looking for efficient methods to generate the spin current. The photogalvanic effect, a phenomenon characterized by the generation of DC current from light illumination, is particularly useful in this regard. Studies have found that a photogalvanic spin current can be generated similarly using the magnetic fields in electromagnetic waves. However, we currently lack candidate materials and a general mathematical formulation for exploring this phenomenon.