Physics News and Discussions

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Experiments reveal formation of a new state of matter: Electron quadruplets
https://phys.org/news/2021-10-reveal-fo ... plets.html
by KTH Royal Institute of Technology
The central principle of superconductivity is that electrons form pairs. But can they also condense into foursomes? Recent findings have suggested they can, and a physicist at KTH Royal Institute of Technology today published the first experimental evidence of this quadrupling effect and the mechanism by which this state of matter occurs.

Reporting today in Nature Physics, Professor Egor Babaev and collaborators presented evidence of fermion quadrupling in a series of experimental measurements on the iron-based material, Ba1−xKxFe2As2. The results follow nearly 20 years after Babaev first predicted this kind of phenomenon, and eight years after he published a paper predicting that it could occur in the material.

The pairing of electrons enables the quantum state of superconductivity, a zero-resistance state of conductivity which is used in MRI scanners and quantum computing. It occurs within a material as a result of two electrons bonding rather than repelling each other, as they would in a vacuum. The phenomenon was first described in a theory by, Leon Cooper, John Bardeen and John Schrieffer, whose work was awarded the Nobel Prize in 1972.
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Physicists announce results that boost evidence for new fundamental physics

by University of Cambridge
https://phys.org/news/2021-10-physicist ... ental.html
Results announced by the LHCb experiment at CERN have revealed further hints for phenomena that cannot be explained by our current theory of fundamental physics.

In March 2020, the same experiment released evidence of particles breaking one of the core principles of the Standard Model—our best theory of particles and forces—suggesting the possible existence of new fundamental particles and forces.

Now, further measurements by physicists at Cambridge's Cavendish Laboratory have found similar effects, boosting the case for new physics.

The Standard Model describes all the known particles that make up the universe and the forces that they interact through. It has passed every experimental test to date, and yet physicists know it must be incomplete. It does not include the force of gravity, nor can it account for how matter was produced during the Big Bang, and contains no particle that could explain the mysterious dark matter that astronomy tells us is five times more abundant than the stuff that makes up the visible world around us.

As a result, physicists have long been hunting for signs of physics beyond the Standard Model that might help us to address some of these mysteries.

One of the best ways to search for new particles and forces is to study particles known as beauty quarks. These are exotic cousins of the up and down quarks that make up the nucleus of every atom.
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New photonic chip for isolating light may be key to miniaturizing quantum devices
https://phys.org/news/2021-10-photonic- ... izing.html
by University of Illinois at Urbana-Champaign
Light offers an irreplaceable way to interact with our universe. It can travel across galactic distances and collide with our atmosphere, creating a shower of particles that tell a story of past astronomical events. Here on earth, controlling light lets us send data from one side of the planet to the other.

Given its broad utility, it's no surprise that light plays a critical role in enabling 21st century quantum information applications. For example, scientists use laser light to precisely control atoms, turning them into ultra-sensitive measures of time, acceleration, and even gravity. Currently, such early quantum technology is limited by size—state-of-the-art systems would not fit on a dining room table, let alone a chip. For practical use, scientists and engineers need to miniaturize quantum devices, which requires re-thinking certain components for harnessing light.

Now IQUIST member Gaurav Bahl and his research group have designed a simple, compact photonic circuit that uses sound waves to rein in light. The new study, published in the October 21 issue of the journal Nature Photonics, demonstrates a powerful way to isolate, or control the directionality of light. The team's measurements show that their approach to isolation currently outperforms all previous on-chip alternatives and is optimized for compatibility with atom-based sensors.

"Atoms are the perfect references anywhere in nature and provide a basis for many quantum applications," said Bahl, a professor in Mechanical Science and Engineering (MechSe) at the University of Illinois at Urbana-Champaign. "The lasers that we use to control atoms need isolators that block undesirable reflections. But so far the isolators that work well in large-scale experiments have proved tough to miniaturize."
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'Raindrops on the roof-technique' reveals new quantum liquid
https://phys.org/news/2021-10-raindrops ... iquid.html
by Bruno Van Wayenburg, Leiden Institute of Physics
Koen Bastiaans and his colleagues have discovered a new quantum liquid unlike anything ever seen. They did it by using a technique that can be compared to listening to the sound of raindrops falling on a roof.

Perhaps you still remember those old-fashioned light bulbs; they gave a cozy glow, they got hot, and nowadays they would greatly increase your electricity bill. Why? They were made out of a material with a large electrical resistance. All materials have a certain resistance to conducting electricity.

All materials? Yes, except for a special class of materials called superconductors. These transport electricity without any resistance when they are cooled below certain (extremely low) temperatures. How they work is one of the enduring mysteries of physics.
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Researchers develop a new way to control and measure energy levels in a diamond crystal
https://phys.org/news/2021-10-energy-di ... ystal.html
by Massachusetts Institute of Technology
Physicists and engineers have long been interested in creating new forms of matter, those not typically found in nature. Such materials might find use someday in, for example, novel computer chips. Beyond applications, they also reveal elusive insights about the fundamental workings of the universe. Recent work at MIT both created and characterized new quantum systems demonstrating dynamical symmetry—particular kinds of behavior that repeat periodically, like a shape folded and reflected through time.

"There are two problems we needed to solve," says Changhao Li, a graduate student in the lab of Paola Cappellaro, a professor of nuclear science and engineering. Li published the work recently in Physical Review Letters, together with Cappellaro and fellow graduate student Guoqing Wang. "The first problem was that we needed to engineer such a system. And second, how do we characterize it? How do we observe this symmetry?"

Concretely, the quantum system consisted of a diamond crystal about a millimeter across. The crystal contains many imperfections caused by a nitrogen atom next to a gap in the lattice—a so-called nitrogen-vacancy center. Just like an electron, each center has a quantum property called a spin, with two discrete energy levels. Because the system is a quantum system, the spins can be found not only in one of the levels, but also in a combination of both energy levels, like Schrodinger's theoretical cat, which can be both alive and dead at the same time.
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Physicists discover how particles self-assemble
https://phys.org/news/2021-11-physicist ... emble.html
by New York University
A team of physicists has discovered how DNA molecules self-organize into adhesive patches between particles in response to assembly instructions. Its findings offer a "proof of concept" for an innovative way to produce materials with a well-defined connectivity between the particles.

The work is reported in Proceedings of the National Academy of Sciences.

"We show that one can program particles to make tailored structures with customized properties," explains Jasna Brujic, a professor in New York University's Department of Physics and one of the researchers. "While cranes, drills, and hammers must be controlled by humans in constructing buildings, this work reveals how one can use physics to make smart materials that 'know' how to assemble themselves."

Scientists have long sought a means for molecules to self-assemble and have achieved breakthroughs on many fronts. However, less developed are measures in which these tiny particles self-assemble with a preprogrammed number of bonds.

To address this, Brujic and her colleagues, Angus McMullen, a postdoctoral researcher in NYU's Department of Physics, and Sascha Hilgenfeldt, a professor of mechanical science and engineering at the University of Illinois, Urbana-Champaign, ran a series of experiments to capture—and manipulate—the behavior of DNA molecules on particle surfaces.
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Fundamental Quantum Theorem Applies to Temperatures Beyond Absolute Zero
November 11, 2021 by Brian Wang
https://www.nextbigfuture.com/2021/11/173732.html
The adiabatic theorem – a fundamental achievement of quantum mechanics – was first formulated by Max Born and Vladimir Fock at the dawn of quantum mechanics. The theorem ensures that the evolving quantum state always remains close the so-called instantaneous eigenstate if external parameters change slowly enough. In a sense, adiabatic evolution is something like taking a class of first-graders on a tour of a museum: you should lead your class carefully and without haste to make sure that by the end of the tour no one’s missing and all the exhibits are intact.

Above – A quantum spin is moved around a wire along a circular trajectory. Electrons in the wire are magnetically coupled to the spin due to fluctuations of the current. The many-body adiabaticity of the electron-spin system at finite temperature is robust with respect to increasing the length of the wire. In contract, the pure state adiabaticity breaks down at any finite driving rate.

Although the adiabatic theorem has been refined and improved since Born and Fock’s time, its major limitation was that it worked only for the so called pure states but not all quantum states. This means that it could be applied to systems at absolute zero only but never at finite temperatures. In our museum example, the tour could go off without a hitch only if the class consisted of well-behaved straight-A pupils, which is hardly possible in real life. Just as there can be no class without naughty kids, there can be no strictly zero temperature.
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Quantum confinement discovered in porous nano-photocatalyst
https://phys.org/news/2021-11-quantum-c ... alyst.html
by City University of Hong Kong
The City University of Hong Kong research team used this photocatalytic reactor to do experiments on the hydrogen-producing photocatalyst. Credit: City University of Hong Kong

Green hydrogen production from solar water splitting has attracted a great deal of interest in recent years because hydrogen is a fuel of high energy density. A research team co-led by scholars from City University of Hong Kong (CityU) and Germany discovered the quantum confinement effect in a photocatalyst of a 3D-ordered macroporous structure. The quantum confinement effect was found to enable hydrogen production under visible light. The findings offer an option for addressing energy and environmental challenges.

The research was co-led by Dr. Ng Yun Hau, Associate Professor in CityU's School of Energy and Environment (SEE), and researchers from Germany. Their findings were published in the scientific journal ACS Energy Letters, titled "Unveiling Carrier Dynamics in Periodic Porous BiVO4 Photocatalyst for Enhanced Solar Water Splitting."
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A computer algorithm that speeds up experiments on plasma
https://phys.org/news/2021-11-algorithm-plasma.html
by Bob Yirka , Phys.org

A team of researchers from Tri Alpha Energy Inc. and Google has developed an algorithm that can be used to speed up experiments conducted with plasma. In their paper published in the journal Scientific Reports, the group describes how they plan to use the algorithm in nuclear fusion research.

As research into harnessing nuclear fusion has progressed, scientists have found that some of its characteristics are too complex to be solved in a reasonable amount of time using current technology. So they have increasingly turned to computers to help. More specifically, they want to adjust certain parameters in a device created to achieve fusion in a reasonable way. Such a device, most in the field agree, must involve the creation of a certain type of plasma that is not too hot or too cold, is stable, and has a certain desired density.

Finding the right parameters that meet these conditions has involved an incredible amount of trial and error. In this new effort, the researchers sought to reduce the workload by using a computer to reduce some of the needed trials. To that end, they have created what they call the "optometrist's algorithm." In its most basic sense, it works like an optometrist attempting to measure the visual ability of a patient by showing them images and asking if they are better or worse than other images. The idea is to use the crunching power of a computer with the intelligence of a human being—the computer generates the options and the human tells it whether a given option is better or worse.
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Scientists Observe Quantum Spin Liquids: A State of Matter We've Never Seen Before
DAVID NIELD
7 DECEMBER 2021
An exotic and totally new state of matter called a quantum spin liquid has been hypothesized for decades, and now scientists have been able to observe it in a laboratory for the first time.

The 'liquid' part refers to electrons that are constantly changing and fluctuating inside a magnetic material at low temperatures. Unlike regular magnets, in this case the electrons don't stabilize or settle into the structured lattice of a solid as they are cooled.

The 'quantum spin' refers to orientation of angular momentum (up or down) carried by particles, which are entangled in pairs with opposing spins. Now that the state has been observed for the first time, it's hoped that the discovery can advance progress in the development of quantum computers.

"It is a very special moment in the field," says quantum physicist Mikhail Lukin, from Harvard University in Massachusetts. "You can really touch, poke, and prod at this exotic state and manipulate it to understand its properties... it's a new state of matter that people have never been able to observe."
https://www.sciencealert.com/scientists ... GZmYSqPps8
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