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Tag: quantum technology

  • Physicists Decode Particle Dance That ‘Kills’ Electrical Conductivity

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    When things don’t make sense in the quantum realm, scientists don’t always get to find a good explanation for what they’re seeing. Many times, they arrive at a solution by accident—something that usually begins with the realization that a weird signal is not a wrong signal.

    Researchers had known about an odd phenomenon in which an initially conductive material seemingly loses its ability to conduct electricity altogether. Although physicists suspected electrons were involved, they struggled to pinpoint the exact mechanism. But a new paper published in Physical Review Letters identifies the culprit—or, rather, culprits—behind this disappearing act: an amalgamation of particles referred to as polarons.

    This specific arrangement creates a strange “dance” between the electrons and surrounding atoms that eventually blocks the flow of electricity in the material, according to the researchers. The findings represent the first time polarons were found inside a compound based on thulium, selenium, and tellurium—rare earth metals key to the fabrication of advanced technologies.

    “The fact that we were able to make it visible here for the first time shows what interesting new phenomena are still to be discovered in the quantum cosmos of materials,” Kai Rossnagel, study senior author and scientist at the DESY Institute in Germany, said in a statement.

    Not many, but one

    Polarons belong to a family of strange quantum bodies called quasiparticles. Simply put, quasiparticles describe how, under some circumstances, a group of particles will behave collectively as one particle. Polarons characterize the interaction between electrons and atoms, in this case the rare metal compound. The slightly distorted atomic layers drastically slow down the electrons, putting a damper on the flow of electrons—electricity.

    These transitions “show that the properties of a material cannot be explained by its chemical composition alone,” noted the researchers in the statement. Electrons tend to be privy to the movements of other electrons nearby and will easily move together as quasiparticles, they added, in the process “forming particle-like states with new properties.”

    An odd little bump

    The team initially set out to investigate the general properties of the thulium-based compound. They carried out various measurements of the material using different radiation sources, including intense X-rays at particle accelerators. For some reason, they kept seeing a tiny bump next to the main signal.

    As per usual, they waved it off as a technical error, but the bump persisted throughout the various measurements. At this point, the researchers decided to embark on a focused investigation of the signal—a project that ended up taking years to complete.

    It was when they brought in a 70-year-old model that the calculations finally made sense. Essentially, the small bump was the product of electrons vibrating together with the atoms of the metal compound as a polaron, according to the paper.

    “That was the decisive step,” explained Chul-Hee Min, study lead author and a physicist at Kiel University in Germany, in the statement. “As soon as we included this interaction in the calculations, the simulation and measurements matched perfectly.”

    What’s more, it’s already known to physicists that many modern quantum materials display similar properties. If researchers can better harness these odd electronic properties, polarons could hasten the arrival of materials such as room-temperature superconductors.

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    Gayoung Lee

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  • Physicists Made a Time Crystal We Can Actually See

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    Of all the eccentricities of the quantum realm, time crystals—atomic arrangements that repeat certain motions over time—might be some of the weirdest. But they certainly exist, and to provide more solid proof, physicists have finally created a time crystal we can actually see.

    In a recent Nature Materials paper, physicists at the University of Colorado Boulder presented a new time crystal design: a glass cell filled with liquid crystals—rod-shaped molecules stuck in strange limbo between solid and liquid. It’s the same stuff found in smartphone LCD screens. When hit with light, the crystals jiggle and dance in repeating patterns that the researchers say resemble “psychedelic tiger stripes.”

    “They can be observed directly under a microscope and even, under special conditions, by the naked eye,” said Hanqing Zhao, study lead author and a graduate student at the University of Colorado Boulder, in a release. Technically, these crystalline dances can last for hours, like an “eternally spinning clock,” the researchers added.

    An asymmetrical curiosity

    Time crystals first appeared in a 2012 paper by Nobel laureate Frank Wilczek, who pitched an idea for an impossible crystal that breaks several rules of symmetry in physics. Specifically, a time crystal breaks symmetry because its atoms do not lock into a continuous lattice, and their positions change over time.

    Physicists have since demonstrated versions of Wilczek’s proposal, but these crystals lasted for a terribly short time and were microscopic. Zhao and Ivan Smalyukh, the study’s senior author and a physicist at the University of Colorado Boulder, wanted to see if they could overcome these limitations.

    Finding the molecular ‘kink’

    For the new time crystal, the duo exploited the molecules’ “kinks”—their tendency to cluster together when squeezed in a certain way. Once together, these kinks behave like whole atoms, the researchers explained.

    “You have these twists, and you can’t easily remove them,” Smalyukh said. “They behave like particles and start interacting with each other.”

    The team coated two glass cells with dye molecules, sandwiching a liquid crystal solution between the layers. When they flashed the setup with polarized light, the dye molecules churned inside the glass, squeezing the liquid crystal. This formed thousands of new kinks inside the crystal, the researchers explained.

    “That’s the beauty of this time crystal,” said Smalyukh. “You just create some conditions that aren’t that special. You shine a light, and the whole thing happens.”

    The team believes its iteration of the time crystal could have practical uses. For instance, a “time watermark” printed on bills could be used to identify counterfeits. Also, stacked layers could serve as a tiny data center.

    It’s rare for quantum systems to be visible to the naked eye. Only time will tell if this time crystal amounts to anything—the researchers “don’t want to put a limit on the applications right now”—but even if it doesn’t, it’s still a neat demonstration of how physical theories exist in strange, unexpected corners of reality.

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    Gayoung Lee

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