Physics News and Discussions

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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.
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