Physics News and Discussions

[wjfox]

Acoustic tweezers can pick up objects without physical contact

July 26, 2021

Researchers from Tokyo Metropolitan University have developed a new technology which allows non-contact manipulation of small objects using sound waves. They used a hemispherical array of ultrasound transducers to generate a 3D acoustic field that stably trapped and lifted a small polystyrene ball from a reflective surface. Their technique employs a method similar to laser trapping in biology, but adaptable to a wider range of particle sizes and materials.

https://phys.org/news/2021-07-acoustic- ... ntact.html

[Yuli Ban]

Famous Einstein equation used to create matter from light for first time

In a stunning demonstration of one of Einstein's most famous equations, physicists are claiming to have created matter from pure light for the very first time.

Albert Einstein's famous E=mc2 equation says that if you smash two sufficiently energetic photons, or light particles, into each other, you should be able to create matter in the form of an electron and its antimatter opposite, a positron.

But this process, first described by American physicists Gregory Breit and John Wheeler in 1934, has long been one of the most difficult to observe in physics — mainly because the colliding photons would need to be highly energetic gamma rays, and scientists are not yet able to make gamma ray lasers. Alternative experiments have shown matter being produced from multiple photons, but never in the one to one way needed to most conclusively prove the effect.

[weatheriscool]

Scientists get photons to interact with pairs of atoms for the first time
https://phys.org/news/2021-08-scientist ... atoms.html

Physicists at EPFL have found a way to get photons to interact with pairs of atoms for the first time. The breakthrough is important for the field of cavity quantum electrodynamics (QED), a cutting-edge field leading the way to quantum technologies.

There is no doubt that we are moving steadily toward an era of technologies based on quantum physics. But to get there, we first have to master the ability to make light interact with matter—or more technically, photons with atoms.

This has already been achieved to some degree, giving us the cutting-edge field of cavity quantum electrodynamics (QED), which is already used in quantum networks and quantum information processing. Nonetheless, there are still a long way to go. Current light-matter interactions are limited to individual atoms, which limits our ability to study them in the sort of complex systems involved in quantum-based technologies.

In a paper published in Nature, researchers from the group of Jean-Philippe Brantut at EPFL's School of Basic Sciences have found a way to get photons to 'mix' with pairs of atoms at ultra-low temperatures.

[weatheriscool]

Unified theory explains how materials transform from solids to liquids
https://phys.org/news/2021-09-theory-ma ... quids.html
by Lois Yoksoulian, University of Illinois at Urbana-Champaign

Years of meticulous experimentation have paid off for researchers aiming to unify the physics that defines materials that transition from solids to liquids. The researchers said a new theoretical model could help develop new synthetic materials and inform and predict civil engineering and environmental challenges such as mudslides, dam breaks and avalanches.

The study, led by University of Illinois Urbana-Champaign chemical and biomolecular engineering professor Simon Rogers, unveils a unified mathematical expression that defines how soft-yet-rigid materials transition from a solid into a liquid flow when they exceed their specific stress threshold. The findings are published in the journal Physical Review Letters.

[weatheriscool]

Researchers realize a spin field-effect transistor at room temperature
https://phys.org/news/2021-09-field-eff ... ature.html
by Ingrid Fadelli , Phys.org

A crucial goal of spintronics research is to coherently manipulate electron spins at room temperature using electrical current. This is particularly valuable as it would enable the development of numerous devices, including spin field-effect transistors.

In experiments using conventional materials, engineers and physicists have so far only observed coherent spin precession in the ballistic regime and at very low temperatures. Two-dimensional (2D materials), however, have unique characteristics that could provide new control knobs to manipulate spin procession.

Researchers at CIC nanoGUNE BRTA in Spain and University of Regensburg in Germany have recently demonstrated spin precession at room temperature in the absence of a magnetic field in bilayer graphene. In their paper, published in Physical Review Letters, they used 2D materials to realize a spin field-effect transistor.

"In our group, there is a long tradition of studying spin transport in multiple materials, such as simple metals, for instance," Josep Ingla-Aynes, Franz Herling, Jaroslav Fabian, Luis E. Hueso and Felix Casanova, the researchers who carried out the study, told Phys.org via email. "Our main goal is to understand how the spin of the electron can carry information and how this degree of freedom can help to create devices with new functionalities."

[weatheriscool]

Groundbreaking technique yields important new details on silicon, subatomic particles and possible 'fifth force'
https://phys.org/news/2021-09-groundbre ... licon.html
by National Institute of Standards and Technology

Using a groundbreaking new technique at the National Institute of Standards and Technology (NIST), an international collaboration led by NIST researchers has revealed previously unrecognized properties of technologically crucial silicon crystals and uncovered new information about an important subatomic particle and a long-theorized fifth force of nature.

By aiming subatomic particles known as neutrons at silicon crystals and monitoring the outcome with exquisite sensitivity, the NIST scientists were able to obtain three extraordinary results: the first measurement of a key neutron property in 20 years using a unique method; the highest-precision measurements of the effects of heat-related vibrations in a silicon crystal; and limits on the strength of a possible "fifth force" beyond standard physics theories.

The researchers report their findings in the journal Science.

[weatheriscool]

Researchers report an insulator made of two conductors

by ETH Zurich
https://phys.org/news/2021-09-insulator-conductors.html

Ohm's law is well-known from physics class. It states that the resistance of a conductor and the voltage applied to it determine how much current will flow through the conductor. The electrons in the material—the negatively charged carriers—move in a disordered fashion and largely independently of each other. Physicists find it far more interesting, however, when the charge carriers influence one another strongly enough for that simple picture not to be correct anymore.

This is the case, for instance, in "Twisted Bilayer Graphene," which was discovered a few years ago. That material is made from two wafer-thin graphene layers consisting of a single layer of carbon atoms each. If two neighboring layers are slightly twisted with respect to each other, the electrons can be influenced in such a way that they interact strongly with one another. As a consequence, the material can, for instance, become superconducting and hence conduct current without any losses.

[weatheriscool]

Study provides evidence for 'new physics'
https://phys.org/news/2021-09-evidence-physics.html
by University of Bonn

Is the Standard Model of particle physics incorrect at key points? Recently there has been an increase in experimental observations that deviate from the predictions of this widely accepted physical theory. A current study by the University of Bonn now provides even stronger evidence for the existence of "new physics." The final version of the paper is now published in the journal Physics Letters B. Lead author Chien-Yeah Seng will present the results in mid-October at the fall meeting of the U.S. Physical Society.

The Standard Model of particle physics describes the building blocks that make up the world—us humans, the grains of sand on the beach, the ocean water in which we cool ourselves, but also the sun that burns down on us. The Model also explains what forces act between these elementary particles, and allows us to understand many physical phenomena.

"However, there are also questions that this theory cannot answer," explains Dr. Chien-Yeah Seng, a postdoctoral researcher at the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn. "For example, most researchers assume that 95 percent of our universe is made up of dark matter and dark energy, which we cannot detect directly with our measuring instruments. But the existence of these mysterious components cannot be deduced from the Standard Model."

[weatheriscool]

Physicists make square droplets and liquid lattices

by Aalto University
https://phys.org/news/2021-09-physicist ... tices.html

When two substances are brought together, they will eventually settle into a steady state called thermodynamic equilibrium; examples include oil floating on top of water and milk mixing uniformly into coffee. Researchers at Aalto University in Finland wanted to disrupt this sort of state to see what happens—and whether they can control the outcome.

"Things in equilibrium tend to be quite boring," says Professor Jaakko Timonen, whose research group carried out new work published in Science Advances on 15 September. "It's fascinating to drive systems out of equilibrium and see if the non-equilibrium structures can be controlled or be useful. Biological life itself is a good example of truly complex behavior in a bunch of molecules that are out of thermodynamic equilibrium."

In their work, the team used combinations of oils with different dielectric constants and conductivities. They then subjected the liquids to an electric field.

"When we turn on an electric field over the mixture, electrical charge accumulates at the interface between the oils. This charge density shears the interface out of thermodynamic equilibrium and into interesting formations," explains Dr. Nikos Kyriakopoulos, one of the authors of the paper. As well as being disrupted by the electric field, the liquids were confined into a thin, nearly two-dimensional sheet. This combination led to the oils reshaping into various completely unexpected droplets and patterns.

[weatheriscool]

Understanding photon collisions could aid search for physics beyond the Standard Model
https://phys.org/news/2021-09-physicist ... uture.html
by Jade Boyd, Rice University

Hot on the heels of proving an 87-year-old prediction that matter can be generated directly from light, Rice University physicists and their colleagues have detailed how that process may impact future studies of primordial plasma and physics beyond the Standard Model.

"We are essentially looking at collisions of light," said Wei Li, an associate professor of physics and astronomy at Rice and co-author of the study published in Physical Review Letters.

"We know from Einstein that energy can be converted into mass," said Li, a particle physicist who collaborates with hundreds of colleagues on experiments at high-energy particle accelerators like the European Organization for Nuclear Research's Large Hadron Collider (LHC) and Brookhaven National Laboratory's Relativistic Heavy Ion Collider(RHIC).

Accelerators like RHIC and LHC routinely turn energy into matter by accelerating pieces of atoms near the speed of light and smashing them into one another. The 2012 discovery of the Higgs particle at the LHC is a notable example. At the time, the Higgs was the final unobserved particle in the Standard Model, a theory that describes the fundamental forces and building blocks of atoms.

[weatheriscool]

Nano-scale discovery could help to cool down overheating in electronics
https://phys.org/news/2021-09-nano-scal ... onics.html
by Daniel Strain, University of Colorado at Boulder

A team of physicists at CU Boulder has solved the mystery behind a perplexing phenomenon in the nano realm: why some ultra-small heat sources cool down faster if you pack them closer together. The findings, published today in the journal Proceedings of the National Academy of Sciences (PNAS), could one day help the tech industry design faster electronic devices that overheat less.

"Often, heat is a challenging consideration in designing electronics. You build a device then discover that it's heating up faster than desired," said study co-author Joshua Knobloch, postdoctoral research associate at JILA, a joint research institute between CU Boulder and the National Institute of Standards and Technology (NIST). "Our goal is to understand the fundamental physics involved so we can engineer future devices to efficiently manage the flow of heat."

[weatheriscool]

Quasi-particles with tunable interactions
https://phys.org/news/2021-09-quasi-par ... tions.html
by University ofAmsterdam

The laws of quantum mechanics allow for the existence of 'quasi-particles': excitations in materials that behave exactly like ordinary particles. A major advantage of quasi-particles over ordinary particles is that their properties can be engineered. In a Nature Materials News & Views article this week, IoP physicist Erik van Heumen describes recent experiments where even the interactions between quasi-particles can be tuned.

In recent years, the mathematical branch of topology, studying the shapes of things, and the physical branch of condensed matter physics, studying the behaviour of solids and fluids, have merged into an exciting new research field: that of topological materials. One of the most exciting aspects of this combined field is the emergence of exotic quasi-particles: local disturbances in materials that behave exactly like particles. That such quasi-particles can exist, was already known from the quantum description of simple materials. What the combination with topology offers is a whole new set of such particles, known for example as Dirac and Weyl fermions, axions and magnetic monopoles.

[weatheriscool]

Two-dimensional hybrid metal halide device allows control of terahertz emissions
https://phys.org/news/2021-10-two-dimen ... evice.html
by Tracey Peake, North Carolina State University

Researchers have utilized two-dimensional hybrid metal halides in a device that allows directional control of terahertz radiation generated by a spintronic scheme. The device has better signal efficiency than conventional terahertz generators, and is thinner, lighter and less expensive to produce.

Terahertz (THz) refers to the part of the electromagnetic spectrum (i.e., frequencies between 100 GHz and 10 THz) between microwave and optical, and THz technologies have shown promise for applications ranging from faster computing and communications to sensitive detection equipment. However, creating reliable THz devices has been challenging due to their size, cost and energy conversion inefficiency.

"Ideally, THz devices of the future should be lightweight, low-cost and robust, but that has been difficult to achieve with current materials," says Dali Sun, assistant professor of physics at North Carolina State University and co-corresponding author of the work. "In this work, we found that a 2-D hybrid metal halide commonly used in solar cells and diodes, in conjunction with spintronics, may meet several of these requirements."

[weatheriscool]

Physicists report promising approach to harnessing exotic electronic behavior
https://phys.org/news/2021-10-physicist ... ronic.html
by Elizabeth A. Thomson, Materials Research Laboratory, Massachusetts Institute of Technology

For some 50 years scientists have worked to harness Bloch oscillations, an exotic kind of behavior by electrons that could introduce a new field of physics—and important new technologies—much like more conventional electronic behavior has led to everything from smart watches to computers powerful enough to get us to the Moon.

Now, MIT physicists report on a new approach to achieving Bloch oscillations in recently introduced graphene superlattices. Graphene, a material composed of a single layer of carbon atoms arranged in hexagons resembling a honeycomb structure, is an excellent conductor of electricity. Its electronic properties undergo an interesting transformation in the presence of an "electric mesh" (a periodic potential), resulting in new types of electron behavior not seen in pristine materials. In a recent issue of Physical Review Letters, the scientists outline why graphene superlattices may be game changers in the pursuit of Bloch oscillations.

Normally, electrons exposed to a constant electric field accelerate in a straight line. However, quantum mechanics predicts that electrons in a crystal, or material composed of atoms arranged in an orderly fashion, can behave differently. Upon exposure to an electric field, they can oscillate in tiny waves—Bloch oscillations. "This surprising behavior is an iconic example of coherent dynamics in quantum many-body systems," says Leonid Levitov, an MIT professor of physics and leader of the current work. Levitov is also affiliated with MIT's Materials Research Laboratory.

Additional authors are Ali Fahimniya and Zhiyu Dong, both MIT graduate students in physics, and Egor I. Kiselev of Karlsruher Institut fur Technologie.

[weatheriscool]

Skyrmion research: Braids of nanovortices discovered
https://phys.org/news/2021-10-skyrmion- ... tices.html
by Forschungszentrum Juelich

A team of scientists from Germany, Sweden and China has discovered a new physical phenomenon: complex braided structures made of tiny magnetic vortices known as skyrmions. Skyrmions were first detected experimentally a little over a decade ago and have since been the subject of numerous studies, as well as providing a possible basis for innovative concepts in information processing that offer better performance and lower energy consumption. Furthermore, skyrmions influence the magnetoresistive and thermodynamic properties of a material. The discovery therefore has relevance for both applied and basic research.

Strings, threads and braided structures can be seen everywhere in daily life, from shoelaces, to woolen pullovers, from plaits in a child's hair to the braided steel cables that are used to support countless bridges. These structures are also commonly seen in nature and can, for example, give plant fibers tensile or flexural strength. Physicists at Forschungszentrum Jülich, together with colleagues from Stockholm and Hefei, have discovered that such structures exist on the nanoscale in alloys of iron and the metalloid germanium.

[weatheriscool]

Novel quantum effect discovered in naturally occurring graphene
https://phys.org/news/2021-10-quantum-e ... phene.html
by University of Göttingen

Usually, the electrical resistance of a material depends very much on its physical dimensions and fundamental properties. Under special circumstances, however, this resistance can adopt a fixed value that is independent of the basic material properties and "quantised" (meaning that it changes in discrete steps rather than continuously). This quantisation of electrical resistance normally occurs within strong magnetic fields and at very low temperatures when electrons move in a two-dimensional fashion. Now, a research team led by the University of Göttingen has succeeded in demonstrating this effect at low temperatures in the almost complete absence of a magnetic field in naturally occurring double-layer graphene, which is just two atoms thick. The results of the study have been published in Nature.

The team from the University of Göttingen, Ludwig Maximilian University of Munich and the University of Texas (Dallas) used two-layer graphene in its natural form. The delicate graphene flakes are contacted using standard microfabrication techniques and the flake is positioned so that it is hangs freely like a bridge, held at the edges by two metal contacts. The extremely clean double-layers of graphene show a quantisation of electrical resistance at low temperatures and almost undetectable magnetic fields. In addition, the electrical current flows without any loss of energy. The reason for this is a form of magnetism that is not generated in the usual way as seen in conventional magnets (ie by the alignment of the intrinsic magnetic moments of electrons), but by the motion of the charged particles in the graphene double layer itself.

[caltrek]

What is Chaos? A Complex Systems Scientist Explains
by Mitchell Newbury
October 6, 2021

https://theconversation.com/what-is-cha ... ins-169423

Introduction:

(The Conversation) Chaos evokes images of the dinosaurs running wild in Jurassic Park, or my friend’s toddler ravaging the living room.

In a chaotic world, you never know what to expect. Stuff is happening all the time, driven by any kind of random impulse.

But chaos has a deeper meaning in connection to physics and climate science, related to how certain systems – like the weather or the behavior of a toddler – are fundamentally unpredictable.

Scientists define chaos as the amplified effects of tiny changes in the present moment that lead to long-term unpredictability. Picture two almost identical storylines. In one version, two people bump into each other in a train station; but in the other, the train arrives 10 seconds earlier and the meeting never happens. From then on, the two plot lines might be totally different.

Usually those little details don’t matter, but sometimes tiny differences have consequences that keep compounding. And that compounding is what leads to chaos.

[caltrek]

Epic Particle Collider Experiment in US Could Reveal How Matter Holds Itself Together by Daria Sokhan
October 12, 2021

https://www.sciencealert.com/new-electr ... f-together

Extract:

(Science Alert) When the Nobel Prize-winning US physicist Robert Hofstadter and his team fired highly energetic electrons at a small vial of hydrogen at the Stanford Linear Accelerator Center in 1956, they opened the door to a new era of physics.

…Now a brand-new accelerator, the Electron-Ion Collider, to be built within the decade at the Brookhaven National Laboratory in Long Island, US, with the help of 1,300 scientists from around the world, could help take our understanding of the nucleus to a new level.

The Electron-Ion Collider (EIC) will use a very intense beam of electrons as its probe, with which it will be possible to slice the proton or nucleus open and look at the structure inside it.

It will do that by colliding a beam of electrons with a beam of protons or ions (charged atoms) and look at how the electrons scatter. The ion beam is the first of its kind in the world.

…By studying these processes, myself and other scientists will be able to reveal the structure of protons and neutrons, how it is modified when they are bound by the strong force, and how new hadrons are created.

[weatheriscool]

Researchers realize quantum teleportation onto mechanical motion of silicon beams

by Delft University of Technology
https://phys.org/news/2021-10-quantum-t ... licon.html

Quantum technology typically employs qubits (quantum bits) consisting of, for example, single electrons, photons or atoms. A group of TU Delft researchers has now demonstrated the ability to teleport an arbitrary qubit state from a single photon onto an optomechanical device—consisting of a mechanical structure comprising billions of atoms. Their breakthrough research, now published in Nature Photonics, enables real-world applications such as quantum internet repeater nodes while also allowing quantum mechanics itself to be studied in new ways.

Quantum optomechanics

The field of quantum optomechanics uses optical means to control mechanical motion in the quantum regime. The first quantum effects in microscale mechanical devices were demonstrated about ten years ago. Focused efforts have since resulted in entangled states between optomechanical devices as well as demonstrations of an optomechanical quantum memory. Now, the group of Simon Gröblacher, of the Kavli Institute of Nanoscience and the Department of Quantum Nanoscience at Delft University of Technology, in collaboration with researchers from the University of Campinas in Brazil, has shown the first successful teleportation of an arbitrary optical qubit state onto a micromechanical quantum memory.

[weatheriscool]

Bridging optics and electronics: New spatial light modulator marries optical and electronic realms
https://techxplore.com/news/2021-10-bri ... lator.html
by Leah Burrows, Harvard John A. Paulson School of Engineering and Applied Sciences

Spatial light modulators are common optical components found in everything from home theater projectors to cutting-edge laser imaging and optical computing. These components can control various aspects of a light, such as intensity or and phase , pixel by pixel. Most spatial light modulators today rely on mechanical moving parts to achieve this control but that approach results in bulky and slow optical devices.