Physics News and Discussions

weatheriscool
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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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caltrek
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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
Last edited by caltrek on Wed Aug 17, 2022 2:12 pm, edited 1 time in total.
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weatheriscool
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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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