Physics News and Discussions

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Matter and Antimatter Seem to Respond Equally to Gravity
January 5, 2022

https://www.eurekalert.org/news-releases/939319

Introduction:

(EurekAlert) As part of an experiment to measure—to an extremely precise degree—the charge-to-mass ratios of protons and antiprotons, the RIKEN-led BASE collaboration at CERN, Geneva, Switzerland, has found that, within the uncertainty of the experiment, matter and antimatter respond to gravity in the same way.

Matter and antimatter create some of the most interesting problems in physics today. They are essentially equivalent, except that where a particle has a positive charge its antiparticle has a negative one. In other respects they seem equivalent. However, one of the great mysteries of physics today, known as “baryon asymmetry,” is that, despite the fact that they seem equivalent, the universe seems made up entirely of matter, with very little antimatter. Naturally, scientists around the world are trying hard to find something different between the two, which could explain why we exist.

As part of this quest, scientists have explored whether matter and antimatter interact similarly with gravity, or whether antimatter would experience gravity in a different way than matter, which would violate Einstein’s weak equivalence principle. Now, the BASE collaboration has shown, within strict boundaries, that antimatter does in fact respond to gravity in the same way as matter.

The finding, published in Nature, actually came from a different experiment, which was examining the charge-to-mass ratios of protons and antiprotons, one of the other important measurements that could determine the key difference between the two.

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Physicists detect a hybrid particle held together by uniquely intense 'glue'
https://phys.org/news/2022-01-physicist ... quely.html
by Jennifer Chu, Massachusetts Institute of Technology

In the particle world, sometimes two is better than one. Take, for instance, electron pairs. When two electrons are bound together, they can glide through a material without friction, giving the material special superconducting properties. Such paired electrons, or Cooper pairs, are a kind of hybrid particle—a composite of two particles that behaves as one, with properties that are greater than the sum of its parts.

Now MIT physicists have detected another kind of hybrid particle in an unusual, two-dimensional magnetic material. They determined that the hybrid particle is a mashup of an electron and a phonon (a quasiparticle that is produced from a material's vibrating atoms). When they measured the force between the electron and phonon, they found that the glue—or bond—was 10 times stronger than any other electron-phonon hybrid known to date.

The particle's exceptional bond suggests that its electron and phonon might be tuned in tandem; for instance, any change to the electron should affect the phonon, and vice versa. In principle, an electronic excitation, such as voltage or light, applied to the hybrid particle could stimulate the electron as it normally would, and also affect the phonon, which influences a material's structural or magnetic properties. Such dual control could enable scientists to apply voltage or light to a material to tune not just its electrical properties but also its magnetism.

The results are especially relevant, as the team identified the hybrid particle in nickel phosphorus trisulfide (NiPS3), a two-dimensional material that has attracted recent interest for its magnetic properties. If these properties could be manipulated, for instance through the newly detected hybrid particles, scientists believe the material could one day be useful as a new kind of magnetic semiconductor, which could be made into smaller, faster, and more energy-efficient electronics.

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https://www.newscientist.com/article/mg ... f-physics/

[At half past six on the evening of 20 January 2021, amid the gloom of a long winter lockdown, a small team met on Zoom to share a moment they knew might change physics forever. “I was literally shaking,” says Mitesh Patel at Imperial College London. He and his team were about to “unblind” a long-awaited measurement from the LHCb experiment at the CERN particle physics laboratory near Geneva, Switzerland – one that might, at long last, break the standard model, our current best picture of nature’s fundamental workings.

The measurement concerns subatomic particles known as “beauty” or “bottom” quarks. Over the past few years, their behaviour has hinted at forces beyond our established understanding. Now, with the hints continuing to firm up, and more results imminent, it’s crunch time. If these quarks are acting as they appear to be, then we are not only seeing the influence of an unknown force of nature, but perhaps also the outline of a new, unified theory of particles and forces.

That is a big if – but many particle physicists are on tenterhooks, myself included.”I’ve never seen something like this,” says Gino Isidori, a theorist at the University of Zurich, Switzerland. “I’ve never been so excited in my life.”

For all its dazzling success in describing the basic ingredients of our universe, the standard model of particle physics has many shortcomings. It can’t explain dark matter, the invisible stuff that keeps galaxies from flying apart, or dark energy, which seems to be driving the accelerating expansion of the universe. Nor can it tell us how matter survived the big bang, rather …



Read more: https://www.newscientist.com/article/mg ... YqgE/quote]

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New insight into the internal structure of the proton
https://phys.org/news/2022-01-insight-i ... roton.html
by ATLAS Experiment

While the Large Hadron Collider (LHC) at CERN is well known for smashing protons together, it is actually the quarks and gluons inside the protons—collectively known as partons—that are really interacting. Thus, in order to predict the rate of a process occurring in the LHC—such as the production of a Higgs boson or a yet-unknown particle—physicists have to understand how partons behave within the proton. This behavior is described in parton distribution functions (PDFs), which describe what fraction of a proton's momentum is taken by its constituent quarks and gluons.

Knowledge of these PDFs has traditionally come from lepton–proton colliders, such as HERA at DESY. These machines use point-like particles, such as electrons, to directly probe the partons within the proton. Their research revealed that, in addition to the well-known up and down valence quarks that are inside a proton, there is also a sea of quark–antiquark pairs in the proton. This sea is theoretically made of all types of quarks, bound together by gluons. Now, studies of the LHC's proton–proton collisions are providing a detailed look into PDFs, in particular the proton's gluon and quark-type composition.

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A well-known iron-based magnet is also a potential quantum information material
https://phys.org/news/2022-01-well-know ... antum.html
by Ames Laboratory

Scientists pursuing better performance in a well-known type of iron-based magnet also discovered wide-gap semiconducting behavior and a quantum state useful for quantum information processing—all in a single low-cost material that has been in existence for decades.

Scientists at the U.S. Department of Energy's Critical Materials Institute, or CMI, study ways to make lower-cost, easier-to-obtain materials used as ingredients in technologies that are in demand now or are developing for the future. In this case, the researchers were investigating ways to create a stronger iron-based permanent magnet, something referred to as a "gap" magnet.

Permanent magnets fall into two broad categories. The strongest-performing permanent magnets contain rare-earth metals like samarium, neodymium, and dysprosium—their properties make them the best and often only choice for applications like computer hard disk drives and motors in hybrid and electric vehicles. These magnets are typically expensive, and their rare-earth components can be difficult to obtain. The second, iron-based permanent magnets, are inexpensive and made of readily available materials, but their performance is often too poor for many advanced applications. In between the high performing rare-earth magnets and low-performing iron-based magnets is a "gap," where there is a great need for permanent magnets that perform in the mid-range of desirable properties. Filling that gap reduces the need for rare-earth magnets, and in turn hard to source rare-earth materials.

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Advances in theoretical modeling of atomic nuclei
https://phys.org/news/2022-01-advances- ... uclei.html
by Ana Lopes, CERN

The atomic nucleus is a tough nut to crack. The strong interaction between the protons and neutrons that make it up depends on many quantities, and these particles, collectively known as nucleons, are subject to not only two-body forces but also three-body ones. These and other features make the theoretical modeling of atomic nuclei a challenging endeavor.

In the past few decades, however, ab initio theoretical calculations, which attempt to describe nuclei from first principles, have started to change our understanding of nuclei. These calculations require fewer assumptions than traditional nuclear models, and they have a stronger predictive power. That said, because so far they can only be used to predict the properties of nuclei up to a certain atomic mass, they cannot always be compared with so-called DFT calculations, which are also fundamental and powerful and have been around for longer. Such a comparison is essential to build a nuclear model that is applicable across the board.

In a paper just published in Physical Review Letters, an international team at CERN's ISOLDE facility shows how a unique combination of high-quality experimental data and several ab initio and DFT nuclear-physics calculations has resulted in an excellent agreement between the different calculations, as well as between the data and the calculations.

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Arase satellite uncovers coupling between plasma waves and charged particles in Geospace
https://phys.org/news/2022-01-arase-sat ... lasma.html
by Nagoya University

In a new study published in Physical Review Letters, researchers from Japan show that high-frequency plasma waves in the geospace can generate low-frequency plasma waves through wave-particle interactions by heating up low-energy ions, unveiling a new energy transfer pathway in collisionless plasma.

A prominent signature of plasma—a state of matter characterized by freely roaming charged particles interacting via electromagnetic forces—is the generation of "plasma waves," resulting from an instability of plasma distributions. "Fast magnetosonic waves" (MSWs) are one kind of electromagnetic plasma wave in the geospace. MSWs result from hot protons and are considered "high frequency waves."

Another kind of wave commonly generated in the geospace is the "electromagnetic ion cyclotron" (EMIC) wave, which is considered a "low frequency wave." Recently, satellite observations in the geospace have shown that MSWs and EMIC waves often occur together. However, the mechanism underlying this co-occurrence has remained unclear.

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Fastest-ever study of how electrons respond to X-rays performed
https://phys.org/news/2022-01-fastest-e ... -rays.html
by Hayley Dunning, Imperial College London

A study of electron dynamics timed to millionths of a billionth of a second reveals the damage radiation can do on a molecular level.

The first-of-its kind study used ultrafast X-ray laser pulses to disrupt the electrons in a molecule of nitrous oxide and measure the resultant changes with unprecedented accuracy.

The work, published today in Science, was performed at the Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Centre (SLAC), Stanford, U.S. and was supported by a team of five scientists from Imperial College London.

Conventional X-rays used in imaging and radiotherapy can cause damage to cells, but exactly how on a molecular level is not known. Additionally, new high-intensity and short-pulse-duration X-ray lasers are being proposed to image smaller molecules with greater precision, leading to questions about potential damage this could cause to living tissue.

For the first time, researchers have been able to measure the behavior of electrons in a molecule as it responded to irradiation by ultrafast X-rays on attosecond timescales—less than millionths of a billionth of a second.

Understanding to new limits

Co-author Professor Jon Marangos, from the Department of Physics at Imperial, said: "Being able to reach a few hundred attosecond precision when timing electron dynamics means we can now begin to understand certain phenomena to new limits.

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Physicist solves century old problem of radiation reaction
https://phys.org/news/2022-01-physicist ... ction.html
by Lancaster University

A Lancaster physicist has proposed a radical solution to the question of how a charged particle, such as an electron, responded to its own electromagnetic field.

This question has challenged physicists for over 100 years but mathematical physicist Dr. Jonathan Gratus has suggested an alternative approach—published in the Journal of Physics A: Mathematical and Theoretical with controversial implications.

It is well established that if a point charge accelerates it produces electromagnetic radiation. This radiation has both energy and momentum, which must come from somewhere. It is usually assumed that they come from the energy and momentum of the charged particle, damping the motion.

The history of attempts to calculate this radiation reaction (also known as radiation damping) date back to Lorentz in 1892. Major contributions were then made by many well known physicists including Plank, Abraham, von Laue, Born, Schott, Pauli, Dirac and Landau. Active research continues to this day with many articles published every year.

The challenge is that according to Maxwell's equations, the electric field at the actual point where the point particle is, is infinite. Hence the force on that point particle should also be infinite.

Various methods have been used to renormalise away this infinity. This leads to the well established Lorentz-Abraham-Dirac equation.

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Observation of quantum transport at room temperature in a 2.8-nanometer CNT transistor
https://techxplore.com/news/2022-02-qua ... r-cnt.html
by National Institute for Materials Science

An international joint research team led by the National Institute for Materials Science (NIMS) has developed an in situ transmission electron microscopy (TEM) technique that can be used to precisely manipulate individual molecular structures. Using this technique, the team succeeded in fabricating carbon nanotube (CNT) intramolecular transistors by locally altering the CNT's helical structure, thereby making a portion of it to undergo a metal-to-semiconductor transition in a controlled manner.

Semiconducting CNTs are promising as the channel material for energy-efficient nanotransistors which may be used to create microprocessors superior in performance to currently available silicon microprocessors. However, controlling the electronic properties of CNTs by precisely manipulating their helical structures has been a major challenge.

This joint research team succeeded for the first time in controllably manipulating CNTs' electronic properties by locally altering their helical structures using heat and mechanical strain. Using this technique, the team was then able to fabricate CNT transistors by converting a portion of a metallic CNT into a semiconductor, where the semiconductor nanochannel was covalently bonded to the metallic CNT source and drain. The CNT transistors, with the channel as short as 2.8 nanometers in length, exhibited coherent quantum transport at room temperature—wave-like electron behavior usually observed only at extremely low temperature.

The molecular structure manipulation technique developed in this research may potentially be used to fabricate innovative nanoscale electronic devices. The team plans to use this technique to engineer material structures with atomic-level precision to fabricate electronic and quantum devices composed of individual atomic structures or molecules.

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Mutating quantum particles set in motion
https://phys.org/news/2022-02-mutating- ... otion.html
by Vanessa Bismuth, University of Cambridge

In the world of fundamental particles, you are either a fermion or a boson but a new study from the University of Cambridge shows, for the first time, that one can behave as the other as they move from one place to another.

Researchers from the Cavendish Laboratory have modeled a quantum walk of identical particles that can change their fundamental character by simply hopping across a domain wall in a one-dimensional lattice.

Their findings, published as a Letter in Physical Review Research, open up a window to engineer and control new kinds of collective motion in the quantum world.

All known fundamental particles fall in two groups: either a fermion ("matter particle") or a boson ("force carrier"), depending on how their state is affected when two particles are exchanged. This "exchange statistics" strongly affects their behavior, with fermions (electrons) giving rise to the periodic table of elements and bosons (photons) leading to electromagnetic radiation, energy and light.

In this new study, the theoretical physicists show that, by applying an effective magnetic field that varies in space and with the particle density, it is possible to coax the same particles to behave as bosons in one region and (pseudo)fermions in another. The boundaries separating these regions are invisible to every single particle and, yet, dramatically alters their collective motion, leading to striking phenomena such as particles getting trapped or fragmenting into many wave packets.

"Everything that we see around us is made up of either bosons or fermions. These two groups behave and move completely differently: bosons try to bunch together whereas fermions try to stay separate," explained first author Liam L.H. Lau, who carried out this research during his undergraduate studies at the Cavendish Laboratory and is now a graduate student at Rutgers University.

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New insight into unconventional superconductivity
https://phys.org/news/2022-02-insight-u ... ivity.html
by Miriam Arrell, Paul Scherrer Institute

The kagome pattern, a network of corner-sharing triangles, is well known amongst traditional Japanese basket weavers—and condensed matter physicists. The unusual geometry of metal atoms in the kagome lattice and resulting electron behavior makes it a playground for probing weird and wonderful quantum phenomena that form the basis of next-generation device research.

A key example is unconventional—such as high-temperature—superconductivity, which does not follow the conventional laws of superconductivity. Most superconducting materials exhibit their seemingly magical property of zero resistance at a few degrees Kelvin: temperatures that are simply impractical for most applications. Materials that exhibit so-called 'high-temperature' superconductivity, at temperatures achievable with liquid nitrogen cooling (or even at room temperature), are a tantalizing prospect. Finding and synthesizing new materials that exhibit unconventional superconductivity has become the condensed matter physicist's Holy Grail—but getting there involves a deeper understanding of exotic, topological electronic behavior in materials.

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Neutrinos are lighter than 0.8 electronvolts: Experiment limits neutrino mass with unprecedented precision
https://phys.org/news/2022-02-neutrinos ... trino.html
by Max Planck Society

The international KArlsruhe TRItium Neutrino Experiment (KATRIN), located at Karlsruhe Institute of Technology (KIT), has broken an important barrier in neutrino physics that is relevant for both particle physics and cosmology. Based on data published in the journal Nature Physics, a new upper limit of 0.8 electronvolt (eV) for the mass of the neutrino has been obtained. This first push into the sub-eV mass scale of neutrinos by a model-independent laboratory method allows KATRIN to constrain the mass of these "lightweights of the universe" with unprecedented precision.

Neutrinos are arguably the most fascinating elementary particle in our universe. In cosmology they play an important role in the formation of large-scale structures, while in particle physics their tiny but non-zero mass sets them apart, pointing to new physics phenomena beyond our current theories. Without a measurement of the mass scale of neutrinos our understanding of the universe will remain incomplete.

This is the challenge the international KATRIN experiment at Karlsruhe Institute of Technology (KIT) with partners from six countries has taken up as the world's most sensitive scale for neutrinos. It makes use of the beta decay of tritium, an unstable hydrogen isotope, to determine the mass of the neutrino via the energy distribution of electrons released in the decay process. This necessitates a major technological effort: the 70 meter long experiment houses the world's most intense tritium source as well as a giant spectrometer to measure the energy of decay electrons with unprecedented precision.

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Physicists measure gravitational time warp to within one millimeter
By Michael Irving
February 17, 2022
https://newatlas.com/physics/gravity-ti ... illimeter/

The flow of time isn’t as consistent as we might think – gravity slows it down, so clocks on the surface of Earth tick slower than those in space. Now researchers have measured time passing at different speeds across just one millimeter, the smallest distance yet.

The idea that time would be affected by gravity was first proposed by Albert Einstein in 1915, as part of his theory of general relativity. Space and time are inextricably linked, and large masses warp the fabric of spacetime with their immense gravitational influence. This has the effect of making time pass more slowly closer to a large mass like a planet, star, or, in the most extreme example, a black hole. This phenomenon is known as time dilation.

Here on Earth, time dilation effectively means that time moves more quickly at higher elevations. So for instance, time passes faster on the summit of Mount Everest than at sea level, but it applies over smaller distances too – someone living in a 10th floor apartment will age faster than someone on the first floor, and your head ages faster than your feet.

Of course, the differences in the passage of time across these distances are so tiny as to be unnoticeable, but they can be measured using atomic clocks, which keep time very precisely using the reliable ticks of atoms. By comparing atomic clocks on satellites and planes to those on the ground, scientists have been able to measure time dilation over distances of up to thousands of kilometers. But in a new study, researchers at JILA have measured time dilation over the smallest distance yet – just one millimeter.

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Physicists harness electrons to make 'synthetic dimensions'
https://phys.org/news/2022-02-physicist ... sions.html
by Rice University

Our spatial sense doesn't extend beyond the familiar three dimensions, but that doesn't stop scientists from playing with whatever lies beyond.

Rice University physicists are pushing spatial boundaries in new experiments. They've learned to control electrons in gigantic Rydberg atoms with such precision they can create "synthetic dimensions," important tools for quantum simulations.

The Rice team developed a technique to engineer the Rydberg states of ultracold strontium atoms by applying resonant microwave electric fields to couple many states together. A Rydberg state occurs when one electron in the atom is energetically bumped up to a highly excited state, supersizing its orbit to make the atom thousands of times larger than normal.

Ultracold Rydberg atoms are about a millionth of a degree above absolute zero. By precisely and flexibly manipulating the electron motion, Rice Quantum Initiative researchers coupled latticelike Rydberg levels in ways that simulate aspects of real materials. The techniques could also help realize systems that can't be achieved in real three-dimensional space, creating a powerful new platform for quantum research.

Rice physicists Tom Killian, Barry Dunning and Kaden Hazzard, all members of the initiative, detailed the research along with lead author and graduate student Soumya Kanungo in a paper published in Nature Communications. The study built off previous work on Rydberg atoms that Killian and Dunning first explored in 2018.

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New fast-switching electrochromic devices based on an all-solid-state tandem structure
https://techxplore.com/news/2022-02-fas ... state.html
by Ingrid Fadelli , Tech Xplore

In recent years, engineers have been developing a wide variety of innovative and promising electronic devices. Among these are electrochromic devices (ECDs), systems that can control optical properties, such as the transmission, absorption, reflection or emittance of light, in reversible ways.

ECDs could have many interesting applications, for instance in the fabrication of smart windows that improve the energy efficiency of buildings, mirrors, and alternative displays for electronic devices. Many electrochromic devices developed in recent years utilize solid-state inorganic or organic materials (e.g., Ta2O5 and ZrO2) as the electrolyte.

Solid-state electrochromic devices have been found to be particularly promising for the creation of smart windows. Nonetheless, these devices have been found to attain limited ion diffusion speeds, which cause them to color and bleach very slowly over time.

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Rsearchers verify relationship between rate of a nonequilibrium process and the rate at which it creates entropy
https://phys.org/news/2022-02-rsearcher ... tropy.html
by Bob Yirka , Phys.org

A team of researchers affiliated with multiple institutions in China has verified the relationship between the rate at which a nonequilibrium process happens and the rate at which it creates entropy. In their paper published in the journal Physical Review Letters, the researchers describe experiments with individual calcium atoms in an ion trap and findings about the relationship between their lifespan and the rate at which they are able to exchange energy using different types of baths.

Two years ago, physicists Massimiliano Esposito and Gianmaria Falasco used a statistical mathematical outline to show that there exists a relationship between the lifetime of a nonequilibrium process and the rate of entropy involved with the process. In this new effort, the researchers tested the ideas described in the work by Esposito and Falasco using trapped calcium ions.

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Physicists test real quantum theory in an optical quantum network
https://phys.org/news/2022-02-physicist ... tical.html
by Ingrid Fadelli , Phys.org

Quantum theory was originally formulated using complex numbers. Nonetheless, when replying to a letter by Hendrik Lorenz, Erwin Schrödinger (one of its founding fathers), wrote: "Using complex numbers in quantum theory is unpleasant and should be objected to. The wave function is surely fundamentally a real function."

In recent years, scientists successfully ruled out any local hidden variable explanation of quantum theory using Bell tests. Later, such tests were generalized to a network with multiple independent hidden variables. In such a quantum network, quantum theory with only real numbers, or "real quantum theory," and standard quantum theory make quantitatively different predictions in some scenarios, enabling experimental tests of the validity of real quantum theory.

Researchers at Southern University of Science and Technology in China, the Austrian Academy of Sciences and other institutes worldwide have recently adapted one of these tests so that they could be implemented in state-of-the-art photonic systems. Their paper, published in Physical Review Letters, experimentally demonstrates the existence of quantum correlations in an optical network that cannot be explained by real quantum theory.

"From the early days of quantum theory, complex numbers were treated more as a mathematical connivence than a fundamental building block," Zizhu Wang, one of the researchers who carried out the study, told Phys.org. "The general debate on the role of complex numbers in quantum theory has continued into the present."

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New simulations refine axion mass, refocusing dark matter search
https://phys.org/news/2022-02-simulatio ... using.html
by University of California - Berkeley

Physicists searching—unsuccessfully—for today's most favored candidate for dark matter, the axion, have been looking in the wrong place, according to a new supercomputer simulation of how axions were produced shortly after the Big Bang 13.6 billion years ago.

Using new calculational techniques and one of the world's largest computers, Benjamin Safdi, assistant professor of physics at the University of California, Berkeley; Malte Buschmann, a postdoctoral research associate at Princeton University; and colleagues at MIT and Lawrence Berkeley National Laboratory simulated the era when axions would have been produced, approximately a billionth of a billionth of a billionth of a second after the universe came into existence and after the epoch of cosmic inflation.