Physics News and Discussions

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Physicists discover light-induced mechanism for controlling ferroelectric polarization
https://phys.org/news/2022-05-physicist ... ation.html
by Matt McGowan, University of Arkansas
By applying light, University of Arkansas physicists Peng Chen and Laurent Bellaiche have discovered a surprising mechanism for controlling ferroelectric polarization in a deterministic manner.

The finding, made possible by the application of ultrafast laser pulses, enriches fundamental physics research by advancing an understanding of the interactions between light and matter.

The research, published May 10 in Nature Communications, is also an important step toward the design and development of superior sensing and data storage in electronic devices.

Ferroelectric materials exhibit ferroelectricity and the ability to polarize spontaneously. Typically, researchers can manipulate and reverse this polarization by the application of an external electric field. Ultrafast interactions between light and matter are another promising route for controlling ferroelectric polarization, but until now researchers have struggled to achieve a light-induced, deterministic control of such polarization.

The researchers discovered a so-called "squeezing effect" in ferroelectric materials subject to femtosecond laser pulses. A femtosecond is one quadrillionth of a second. These pulses destroyed the polarization component that is parallel to the field's direction and created polarization components perpendicular to it. This squeezing effect allowed a deterministic control of the polarization by light.
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Physicists Found a Way to Trigger the Strange Glow of Warp Speed Acceleration
by Mike McCrae
May 11, 2022

Introduction:
(Science Alert) Every time you take a step, space itself glows with a soft warmth.

Called the Fulling–Davies–Unruh effect (or sometimes just Unruh effect if you're pushed for time), this eerie glow of radiation emerging from the vacuum is akin to the mysterious Hawking radiation that's thought to surround black holes.

Only in this case, it's the product of acceleration rather than gravity.

Can't feel it? There's a good reason for that. You'd need to move at an impossible speed to sense even the weakest of Unruh rays.

For now, the effect remains a purely theoretical phenomenon, far beyond our ability to measure. But that could soon change, following a discovery by researchers from the University of Waterloo in Canada and the Massachusetts Institute of Technology (MIT).
Read more: https://www.sciencealert.com/physicists ... warp-speed
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First direct observation of the dead-cone effect in particle physics
https://phys.org/news/2022-05-dead-cone ... ysics.html
by CERN
The ALICE collaboration at the Large Hadron Collider (LHC) has made the first direct observation of the dead-cone effect—a fundamental feature of the theory of the strong force that binds quarks and gluons together into protons, neutrons and, ultimately, all atomic nuclei. In addition to confirming this effect, the observation, reported in a paper published today in Nature, provides direct experimental access to the mass of a single charm quark before it is confined inside hadrons.

"It has been very challenging to observe the dead cone directly," says ALICE spokesperson Luciano Musa. "But, by using three years' worth of data from proton–proton collisions at the LHC and sophisticated data-analysis techniques, we have finally been able to uncover it."

Quarks and gluons, collectively called partons, are produced in particle collisions such as those that take place at the LHC. After their creation, partons undergo a cascade of events called a parton shower, whereby they lose energy by emitting radiation in the form of gluons, which also emit gluons. The radiation pattern of this shower depends on the mass of the gluon-emitting parton and displays a region around the direction of flight of the parton where gluon emission is suppressed—the dead cone.
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Researchers discover new 'unexpected' phenomenon in quantum physics of materials

by Tanner Stening, Northeastern University
https://phys.org/news/2022-05-unexpecte ... rials.html
Researchers at Northeastern have discovered a new quantum phenomenon in a specific class of materials, called antiferromagnetic insulators, that could yield new ways of powering "spintronic" and other technological devices of the future.

The discovery illuminates "how heat flows in a magnetic insulator, [and] how [researchers] can detect that heat flow," says Gregory Fiete, a physics professor at Northeastern and co-author of the research. The novel effects, published in Nature Physics this week and demonstrated experimentally, were observed by combining lanthanum ferrite (LaFeO3) with a layer of platinum or tungsten.

"That layered coupling is what is responsible for the phenomenon," says Arun Bansil, university distinguished professor in the Department of Physics at Northeastern, who also took part in the study.

The discovery may have numerous potential applications, such as improving heat sensors, waste-heat recycling, and other thermoelectric technologies, Bansil says. This phenomenon could even lead to development of a new power source for these—and other—budding technologies. Northeastern graduate student Matt Matzelle and Bernardo Barbiellini, a computational and theoretical physicist at the Lappeenranta University of Technology, who is currently visiting Northeastern, participated in the research.
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Astrophysicists simulate a fuzzy dark matter galactic halo
https://phys.org/news/2022-05-astrophys ... actic.html
by Ingrid Fadelli , Phys.org

Dark matter is a type of matter in the universe that does not absorb, reflect or emit light, which makes it impossible to directly detect. In recent years, astrophysicists and cosmologists worldwide have been trying to indirectly detect this elusive type of matter, to better understand its unique features and composition.

One of the most promising candidates for dark matter is "fuzzy dark matter" a hypothetical form of dark matter that is thought to consist of extremely light scalar particles. This type of matter is known to be difficult to simulate, due to its unique characteristics.

Researchers at Universidad de Zaragoza in Spain and the Institute for Astrophysics in Germany have recently proposed a new method that could be used to simulate the fuzzy dark matter forming a galactic halo. This method, introduced in a paper published in Physical Review Letters, is based on the adaptation of an algorithm that the team introduced in their previous works.

"The numerical challenge for studies focusing on fuzzy dark matter is that its distinguishing features, the granular density fluctuations in collapsed halos and filaments, are orders of magnitude smaller than any cosmological simulation box large enough to accurately capture the dynamics of the cosmic web," Bodo Schwabe, one of the researchers who carried out the study, told Phys.org. "Thus, for years people have tried to combine efficient numerical methods capturing the large-scale dynamics with algorithms that are computationally demanding but can accurately evolve these density fluctuations."
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Axial Higgs mode: Elusive particle discovered in a material through tabletop experiment
https://phys.org/news/2022-06-axial-hig ... ticle.html
by Boston College
An interdisciplinary team led by Boston College physicists has discovered a new particle—or previously undetectable quantum excitation—known as the axial Higgs mode, a magnetic relative of the mass-defining Higgs Boson particle, the team reports in the online edition of the journal Nature.

The detection a decade ago of the long-sought Higgs Boson became central to the understanding of mass. Unlike its parent, axial Higgs mode has a magnetic moment, and that requires a more complex form of the theory to explain its properties, said Boston College Professor of Physics Kenneth Burch, a lead co-author of the report "Axial Higgs Mode Detected by Quantum Pathway Interference in RTe3."

Theories that predicted the existence of such a mode have been invoked to explain "dark matter," the nearly invisible material that makes up much of the universe, but only reveals itself via gravity, Burch said.

Whereas Higgs Boson was revealed by experiments in a massive particle collider, the team focused on RTe3, or rare-earth tritelluride, a well-studied quantum material that can be examined at room temperature in a "tabletop" experimental format.

"It's not every day you find a new particle sitting on your tabletop," Burch said.

RTe3 has properties that mimic the theory that produces the axial Higgs mode, Burch said. But the central challenge in finding Higgs particles in general is their weak coupling to experimental probes, such as beams of light, he said. Similarly, revealing the subtle quantum properties of particles usually requires rather complex experimental setups including enormous magnets and high-powered lasers, while cooling samples to extremely cold temperatures.
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Glimpses of quantum computing phase changes show researchers the tipping point

by Ken Kingery, Duke University
https://phys.org/news/2022-06-glimpses- ... phase.html
Researchers at Duke University and the University of Maryland have used the frequency of measurements on a quantum computer to get a glimpse into the quantum phenomena of phase changes—something analogous to water turning to steam.

By measuring the number of operations that can be implemented on a quantum computing system without triggering the collapse of its quantum state, the researchers gained insight into how other systems—both natural and computational—meet their tipping points between phases. The results also provide guidance for computer scientists working to implement quantum error correction that will eventually enable quantum computers to achieve their full potential.

The results appeared online June 3 in the journal Nature Physics.

When heating water to a boil, the movement of molecules evolves as the temperature changes until it hits a critical point when it starts to turn to steam. In a similar fashion, a quantum computing system can be increasingly manipulated in discrete time steps until its quantum state collapses into a single solution.

"There are deep connections between phases of matter and quantum theory, which is what's so fascinating about it," said Crystal Noel, assistant professor of electrical and computer engineering and physics at Duke. "The quantum computing system is behaving in the same way as quantum systems found in nature—like liquid changing to steam—even though it's digital."
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Researchers observe continuous time crystal
https://phys.org/news/2022-06-crystal.html
by University of Hamburg
Researchers from the Institute of Laser Physics at Universität Hamburg have succeeded for the first time in realizing a time crystal that spontaneously breaks continuous time translation symmetry. They report their observation in a study published online by the journal Science on Thursday, 9 June, 2022.

The idea of a time crystal goes back to Nobel laureate Franck Wilczek, who first proposed the phenomenon. Similar to water spontaneously turning into ice around the freezing point, thereby breaking the translation symmetry of the system, the time translation symmetry in a dynamical many-body system spontaneously breaks when a time crystal is formed.

In recent years, researchers have already observed discrete or Floquet time crystals in periodically driven closed and open quantum systems. "In all previous experiments, however, the continuous-time translation symmetry is broken by a time-periodic drive," says Dr. Hans Keßler from Prof. Andreas Hemmerich's group at the Cluster of Excellence CUI: Advanced Imaging of Matter. "The challenge for us was to realize a system that spontaneously breaks the continuous time translation symmetry."

Using a Bose-Einstein condensate inside an optical high-finesse cavity

In their experiment, the scientists used a Bose-Einstein condensate inside an optical high-finesse cavity. Using a time-independent pump, they observed a limit cycle phase which is characterized by emergent periodic oscillations of the intracavity photon number accompanied by the atomic density cycling through recurring patterns.
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A model that can predict the exact quasi-particle properties of heavy Fermi polarons
https://phys.org/news/2022-06-exact-qua ... fermi.html
by Ingrid Fadelli , Phys.org
Physicists studying quantum many-body physics very rarely reach exact solutions or conclusions, particularly in more than one dimension. This is also true for the Fermi polaron problem, describing instances in which the many-body quantum background is a non-interacting Fermi gas.

The Fermi polaron problem has been studied extensively over the past decade or so. However, predicting the quasi-particle properties of Fermi polarons with high levels of confidence has so far proved to be very challenging.

Researchers at Swinburne University of Technology recently introduced a model that could be used to predict the exact quasi-particle properties of a heavy polaron in Bardeen-Cooper-Schrieffer (BCS) Fermi superfluids. Their paper, published in Physical Review Letters, introduces a theoretical, exact solution for a many-body system, which could eventually be tested and realized in experimental settings.

The recent study builds on one of the team's previous papers published in Physical Review A. This past work specifically focused on crossover polarons with a mobile impurity.

"Our previous work and many other theoretical studies of polarons using various approximation methods give some universal features (such as the existence of attractive/repulsive polarons and a dark continuum)," Jia Wang, one of the researchers who carried out the study, told Phys.org. "We believe that the suppression of multiple quasiparticle excitations in the background medium is the mechanism underlying these features."
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New device gets scientists closer to quantum materials breakthrough
https://phys.org/news/2022-06-device-sc ... rials.html
by Dan Moser, University of Nebraska-Lincoln
Researchers from the University of Nebraska-Lincoln and the University of California, Berkeley, have developed a new photonic device that could get scientists closer to the "holy grail" of finding the global minimum of mathematical formulations at room temperature. Finding that illusive mathematical value would be a major advancement in opening new options for simulations involving quantum materials.

Many scientific questions depend heavily on being able to find that mathematical value, said Wei Bao, Nebraska assistant professor of electrical and computer engineering. The search can be challenging even for modern computers, especially when the dimensions of the parameters—commonly used in quantum physics—are extremely large.

Until now, researchers could only do this with polariton optimization devices at extremely low temperatures, close to about minus 270 degrees Celsius. Bao said the Nebraska-UC Berkeley team "has found a way to combine the advantages of light and matter at room temperature suitable for this great optimization challenge."
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