Physics News and Discussions

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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.
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