Physics News and Discussions

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Theoretical model offers a new perspective on black hole formation and evolution
https://phys.org/news/2022-04-theoretic ... ation.html
by Ingrid Fadelli , Phys.org

Black holes are regions in space characterized by gravitational fields so intense that no matter or radiation can escape from them. They are solutions to Einstein's field equations, with a point of unphysical infinite density at their center.

Based on the classical theory of general relativity, all the matter that went into forming a black hole ultimately ends up at its center. This specific prediction is known as the "singularity problem."

In one of his seminal works, Stephen Hawking showed that black holes radiate energy and that they slowly disappear. However, his work suggests that the radiation emitted by black holes does not contain all the information about the matter that went into its formation. In astrophysics, this is referred to as the "information loss problem."

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Large Hadron Collider restarts after three-year break
https://phys.org/news/2022-04-large-had ... -year.html
by Daniel Lawler and Juliette Collen

The Large Hadron Collider has been closed since December 2018 for maintenance and upgrades.

The Large Hadron Collider restarted Friday after a three-year break for upgrades that will allow it to smash protons together at even greater speeds, in the hope of making new ground-breaking discoveries.

It will further study the Higgs boson, the existence of which it proved in 2012, and put the Standard Model of particle physics to the test after recent anomalies sparked theories about a mysterious fifth force of nature.

"Two beams of protons circulated in opposite directions around the Large Hadron Collider's 27-kilometer (17-mile) ring" just after noon on Friday, Europe's physics lab CERN said in a statement.

Buried more than 100 meters (330 feet) beneath the border of Switzerland and France, the collider has been closed since December 2018 for maintenance and upgrades, the second longest shutdown in its 14-year history.

To start with, the collider is taking it easy.

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Time travel could be possible, but only with parallel timelines
https://phys.org/news/2022-04-parallel-timelines.html
by Barak Shoshany, The Conversation

Have you ever made a mistake that you wish you could undo? Correcting past mistakes is one of the reasons we find the concept of time travel so fascinating. As often portrayed in science fiction, with a time machine, nothing is permanent anymore—you can always go back and change it. But is time travel really possible in our universe, or is it just science fiction?

Our modern understanding of time and causality comes from general relativity. Theoretical physicist Albert Einstein's theory combines space and time into a single entity—"spacetime"—and provides a remarkably intricate explanation of how they both work, at a level unmatched by any other established theory. This theory has existed for more than 100 years, and has been experimentally verified to extremely high precision, so physicists are fairly certain it provides an accurate description of the causal structure of our universe.

For decades, physicists have been trying to use general relativity to figure out if time travel is possible. It turns out that you can write down equations that describe time travel and are fully compatible and consistent with relativity. But physics is not mathematics, and equations are meaningless if they do not correspond to anything in reality.

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New and surprising duality found in theoretical particle physics
https://phys.org/news/2022-04-duality-t ... ysics.html
by Niels Bohr Institute

A new and surprising duality has been discovered in theoretical particle physics. The duality exists between two types of scattering processes that can occur in the proton collisions made in the Large Hadron Collider at CERN in Switzerland and France. The fact that this connection can, surprisingly, be made points to the fact that there is something in the intricate details of the standard model of particle physics that is not fully understood. The standard model is the model of the world on sub-atomic scale that explains all particles and their interactions, so when surprises appear, there is cause for attention. The scientific article is now published in Physical Review Letters.

Duality in physics

The concept of duality occurs in different areas of physics. The most well known duality is probably the particle-wave duality in quantum mechanics. The famous double-slit experiment shows that light behaves like a wave, while Albert Einstein received his Nobel prize for showing that light behaves like a particle.

The strange thing is that light is actually both and neither of the two at the same time. There are simply two ways we can look at this entity, light, and each comes with a mathematical description. Both with a completely different intuitive idea, but still describe the same thing.

[Yuli Ban]

[Yuli Ban]

Time travel could be possible, but only with parallel timelines
https://phys.org/news/2022-04-parallel-timelines.html
by Barak Shoshany, The Conversation

Have you ever made a mistake that you wish you could undo? Correcting past mistakes is one of the reasons we find the concept of time travel so fascinating. As often portrayed in science fiction, with a time machine, nothing is permanent anymore—you can always go back and change it. But is time travel really possible in our universe, or is it just science fiction?

Our modern understanding of time and causality comes from general relativity. Theoretical physicist Albert Einstein's theory combines space and time into a single entity—"spacetime"—and provides a remarkably intricate explanation of how they both work, at a level unmatched by any other established theory. This theory has existed for more than 100 years, and has been experimentally verified to extremely high precision, so physicists are fairly certain it provides an accurate description of the causal structure of our universe.

For decades, physicists have been trying to use general relativity to figure out if time travel is possible. It turns out that you can write down equations that describe time travel and are fully compatible and consistent with relativity. But physics is not mathematics, and equations are meaningless if they do not correspond to anything in reality.

I mean, that sounds like a better deal to me. You basically have an infinite number of possibilities

[raklian]

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Single photon emitter takes a step closer to quantum tech
https://phys.org/news/2022-05-photon-em ... -tech.html
by Raphaël Butté, Nik Papageorgiou, Ecole Polytechnique Federale de Lausanne

To get closer to quantum technology we need to develop non-classical light sources that can emit a single photon at a time and do so on demand. Scientists at EPFL have now designed one of these "single photon emitters" that can work at room temperature and is based on quantum dots grown on cost-effective silicon substrates.

Developing non-classical light sources that can emit, on-demand, exactly one photon at a time is one of the main requirements of quantum technologies. But although the first demonstration of such a "single photon emitter," or SPE, dates back to the 1970s, their low reliability and efficiency has been stood in the way of any meaningfully practical use.

Conventional light sources like incandescent light bulbs or LEDs emit bunches of photons at a time. In other words, their probability to emit a single photon at a time is very low. Laser sources can emit streams of single photons, but not on-demand, which means that, sometimes, there will be no photons whatsoever emitted when we want them to.

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Bilayer graphene inspires two-universe cosmological model

by Bailey Bedford, Joint Quantum Institute
https://phys.org/news/2022-05-bilayer-g ... gical.html

Physicists sometimes come up with crazy stories that sound like science fiction. Some turn out to be true, like how the curvature of space and time described by Einstein was eventually borne out by astronomical measurements. Others linger on as mere possibilities or mathematical curiosities.

In a new paper in Physical Review Research, JQI Fellow Victor Galitski and JQI graduate student Alireza Parhizkar have explored the imaginative possibility that our reality is only one half of a pair of interacting worlds. Their mathematical model may provide a new perspective for looking at fundamental features of reality—including why our universe expands the way it does and how that relates to the most miniscule lengths allowed in quantum mechanics. These topics are crucial to understanding our universe and are part of one of the great mysteries of modern physics.

The pair of scientists stumbled upon this new perspective when they were looking into research on sheets of graphene—single atomic layers of carbon in a repeating hexagonal pattern. They realized that experiments on the electrical properties of stacked sheets of graphene produced results that looked like little universes and that the underlying phenomenon might generalize to other areas of physics. In stacks of graphene, new electrical behaviors arise from interactions between the individual sheets, so maybe unique physics could similarly emerge from interacting layers elsewhere—perhaps in cosmological theories about the entire universe.

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The standard model of particle physics may be broken, expert says
https://phys.org/news/2022-05-standard- ... xpert.html
by Roger Jones, The Conversation

As a physicist working at the Large Hadron Collider (LHC) at Cern, one of the most frequent questions I am asked is "When are you going to find something?" Resisting the temptation to sarcastically reply "Aside from the Higgs boson, which won the Nobel Prize, and a whole slew of new composite particles?" I realize that the reason the question is posed so often is down to how we have portrayed progress in particle physics to the wider world.

We often talk about progress in terms of discovering new particles, and it often is. Studying a new, very heavy particle helps us view underlying physical processes—often without annoying background noise. That makes it easy to explain the value of the discovery to the public and politicians.

Recently, however, a series of precise measurements of already known, bog-standard particles and processes have threatened to shake up physics. And with the LHC getting ready to run at higher energy and intensity than ever before, it is time to start discussing the implications widely.

In truth, particle physics has always proceeded in two ways, of which new particles is one. The other is by making very precise measurements that test the predictions of theories and look for deviations from what is expected.

The early evidence for Einstein's theory of general relativity, for example, came from discovering small deviations in the apparent positions of stars and from the motion of Mercury in its orbit.

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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.

[caltrek]

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."

[weatheriscool]

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."