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  • richardmitnick 4:57 pm on July 17, 2021 Permalink | Reply
    Tags: "Unconventional Superconductor Acts the Part of a Promising Quantum Computing Platform", All superconductors carry electrical currents without any resistance., Majorana modes-exotic particles that behave a bit like half of an electron-are predicted to arise on the surface of topological superconductors., , Scientists on the hunt for an unconventional kind of superconductor have produced the most compelling evidence to date that they’ve found one., Since the early 2000s scientists have been looking for a special kind of superconductor-one that relies on an intricate choreography of the subatomic particles that actually carry its current., University of Maryland (US), Uranium ditelluride (or UTe2 for short) displays many of the hallmarks of a topological superconductor.   

    From University of Maryland (US) : “Unconventional Superconductor Acts the Part of a Promising Quantum Computing Platform” 

    From University of Maryland (US)

    1

    July 15 2021

    Scientists on the hunt for an unconventional kind of superconductor have produced the most compelling evidence to date that they’ve found one. In a pair of papers, researchers at the University of Maryland’s (UMD) Quantum Materials Center (QMC) and colleagues have shown that uranium ditelluride (or UTe2 for short) displays many of the hallmarks of a topological superconductor—a material that may unlock new ways to build quantum computers and other futuristic devices.

    “Nature can be wicked,” says Johnpierre Paglione, a professor of physics at UMD, the director of QMC and senior author on one of the papers. “There could be other reasons we’re seeing all this wacky stuff, but honestly, in my career, I’ve never seen anything like it.”

    All superconductors carry electrical currents without any resistance. It’s kind of their thing. The wiring behind your walls can’t rival this feat, which is one of many reasons that large coils of superconducting wires and not normal copper wires have been used in MRI machines and other scientific equipment for decades.

    1
    Crystals of a promising topological superconductor grown by researchers at the University of Maryland’s Quantum Materials Center. (Credit: Sheng Ran/NIST).

    But superconductors achieve their super-conductance in different ways. Since the early 2000s scientists have been looking for a special kind of superconductor-one that relies on an intricate choreography of the subatomic particles that actually carry its current.

    This choreography has a surprising director: a branch of mathematics called topology. Topology is a way of grouping together shapes that can be gently transformed into one another through pushing and pulling. For example, a ball of dough can be shaped into a loaf of bread or a pizza pie, but you can’t make it into a donut without poking a hole in it. The upshot is that, topologically speaking, a loaf and a pie are identical, while a donut is different. In a topological superconductor, electrons perform a dance around each other while circling something akin to the hole in the center of a donut.

    Unfortunately, there’s no good way to slice a superconductor open and zoom in on these electronic dance moves. At the moment, the best way to tell whether or not electrons are boogieing on an abstract donut is to observe how a material behaves in experiments. Until now, no superconductor has been conclusively shown to be topological, but the new papers show that UTe2 looks, swims and quacks like the right kind of topological duck.

    One study, by Paglione’s team in collaboration with the group of Aharon Kapitulnik at Stanford University (US), reveals that not one but two kinds of superconductivity exist simultaneously in UTe2. Using this result, as well as the way light is altered when it bounces off the material (in addition to previously published experimental evidence), they were able to narrow down the types of superconductivity that are present to two options, both of which theorists believe are topological. They published their findings on July 15, 2021, in the journal Science.

    In another study, a team led by Steven Anlage, a professor of physics at UMD and a member of QMC, revealed unusual behavior on the surface of the same material. Their findings are consistent with the long-sought-after phenomenon of topologically protected Majorana modes. Majorana modes-exotic particles that behave a bit like half of an electron-are predicted to arise on the surface of topological superconductors. These particles particularly excite scientists because they might be a foundation for robust quantum computers. Anlage and his team reported their results in a paper published May 21, 2021 in the journal Nature Communications.

    Superconductors only reveal their special characteristics below a certain temperature, much like water only freezes below zero Celsius. In normal superconductors, electrons pair up into a two-person conga line, following each other through the metal. But in some rare cases, the electron couples perform a circular dance around each other, more akin to a waltz. The topological case is even more special—the circular dance of the electrons contains a vortex, like the eye amidst the swirling winds of a hurricane. Once electrons pair up in this way, the vortex is hard to get rid of, which is what makes a topological superconductor distinct from one with a simple, fair-weather electron dance.

    Back in 2018, Paglione’s team, in collaboration with the team of Nicholas Butch, an adjunct associate professor of physics at UMD and a physicist at the National Institute of Standards and Technology (NIST) (US), unexpectedly discovered that UTe2 was a superconductor. Right away, it was clear that it wasn’t your average superconductor. Most notably, it seemed unphased by large magnetic fields, which normally destroy superconductivity by splitting up the electron dance couples. This was the first clue that the electron pairs in UTe2 hold onto each other more tightly than usual, likely because their paired dance is circular. This garnered a lot of interest and further research from others in the field.

    “It’s kind of like a perfect storm superconductor,” says Anlage. “It’s combining a lot of different things that no one’s ever seen combined before.”

    In the new Science paper, Paglione and his collaborators reported two new measurements that reveal the internal structure of UTe2. The UMD team measured the material’s specific heat, which characterizes how much energy it takes to heat it up by one degree. They measured the specific heat at different starting temperatures and watched it change as the sample became superconducting.

    “Normally there’s a big jump in specific heat at the superconducting transition,” says Paglione. “But we see that there’s actually two jumps. So that’s evidence of actually two superconducting transitions, not just one. And that’s highly unusual.”

    The two jumps suggested that electrons in UTe2 can pair up to perform either of two distinct dance patterns.

    In a second measurement, the Stanford team shone laser light onto a piece of UTe2 and noticed that the light reflecting back was a bit twisted. If they sent in light bobbing up and down, the reflected light bobbed mostly up and down but also a bit left and right. This meant something inside the superconductor was twisting up the light and not untwisting it on its way out.

    Kapitulnik’s team at Stanford also found that a magnetic field could coerce UTe2 into twisting light one way or the other. If they applied a magnetic field pointing up as the sample became superconducting, the light coming out would be tilted to the left. If they pointed the magnetic field down, the light tilted to the right. This told that researchers that, for the electrons dancing inside the sample, there was something special about the up and down directions of the crystal.

    To sort out what all this meant for the electrons dancing in the superconductor, the researchers enlisted the help of Daniel F. Agterberg, a theorist and professor of physics at the University of Wisconsin-Milwaukee (US) and a co-author of the Science paper. According to the theory, the way uranium and tellurium atoms are arranged inside the UTe2 crystal allows electron couples to team up in eight different dance configurations. Since the specific heat measurement shows that two dances are going on at the same time, Agterberg enumerated all the different ways to pair these eight dances together. The twisted nature of the reflected light and the coercive power of a magnetic field along the up-down axis cut the possibilities down to four. Previous results showing the robustness of UTe2’s superconductivity under large magnetic fields further constrained it to only two of those dance pairs, both of which form a vortex and indicate a stormy, topological dance.

    “What’s interesting is that given the constraints of what we’ve seen experimentally, our best theory points to a certainty that the superconducting state is topological,” says Paglione.

    If the nature of superconductivity in a material is topological, the resistance will still go to zero in the bulk of the material, but on the surface something unique will happen: Particles, known as Majorana modes, will appear and form a fluid that is not a superconductor. These particles also remain on the surface despite defects in the material or small disruptions from the environment. Researchers have proposed that, thanks to the unique properties of these particles, they might be a good foundation for quantum computers. Encoding a piece of quantum information into several Majoranas that are far apart makes the information virtually immune to local disturbances that, so far, have been the bane of quantum computers.

    Anlage’s team wanted to probe the surface of UTe2 more directly to see if they could spot signatures of this Majorana sea. To do that, they sent microwaves towards a chunk UTe2, and measured the microwaves that came out on the other side. They compared the output with and without the sample, which allowed them to test properties of the bulk and the surface simultaneously.

    The surface leaves an imprint on the strength of the microwaves, leading to an output that bobs up and down in sync with the input, but slightly subdued. But since the bulk is a superconductor, it offers no resistance to the microwaves and doesn’t change their strength. Instead, it slows them down, causing delays that make the output bob up and down out of sync with the input. By looking at the out-of-sync parts of the response, the researchers determined how many of the electrons inside the material participate in the paired dance at various temperatures. They found that the behavior agreed with the circular dances suggested by Paglione’s team.

    ­­­Perhaps more importantly, the in-sync part of the microwave response showed that the surface of UTe2 isn’t superconducting. This is unusual, since superconductivity is usually contagious: Putting a regular metal close to a superconductor spreads superconductivity to the metal. But the surface of UTe2 didn’t seem to catch superconductivity from the bulk—just as expected for a topological superconductor—and instead responded to the microwaves in a way that hasn’t been seen before.

    “The surface behaves differently from any superconductor we’ve ever looked at,” Anlage says. “And then the question is ‘What’s the interpretation of that anomalous result?’ And one of the interpretations, which would be consistent with all the other data, is that we have this topologically protected surface state that is kind of like a wrapper around the superconductor that you can’t get rid of.”

    It might be tempting to conclude that the surface of UTe2 is covered with a sea of Majorana modes and declare victory. However, extraordinary claims require extraordinary evidence. Anlage and his group have tried to come up with every possible alternative explanation for what they were observing and systematically ruled them out, from oxidization on the surface to light hitting the edges of the sample. Still, it is possible a surprising alternative explanation is yet to be discovered.

    “In the back of your head you’re always thinking ‘Oh, maybe it was cosmic rays’, or ‘Maybe it was something else,’” says Anlage. “You can never 100% eliminate every other possibility.”

    For Paglione’s part, he says the smoking gun will be nothing short of using surface Majorana modes to perform a quantum computation. However, even if the surface of UTe2 truly has a bunch of Majorana modes, there’s currently no straightforward way to isolate and manipulate them. Doing so might be more practical with a thin film of UTe2 instead of the (easier to produce) crystals that were used in these recent experiments.

    “We have some proposals to try to make thin films,” Paglione says. “Because it’s uranium and it’s radioactive, it requires some new equipment. The next task would be to actually try to see if we can grow films. And then the next task would be to try to make devices. So that would require several years, but it’s not crazy.”

    Whether UTe2 proves to be the long-awaited topological superconductor or just a pigeon that learned to swim and quack like a duck, both Paglione and Anlage are excited to keep finding out what the material has in store.

    “It’s pretty clear though that there’s a lot of cool physics in the material,” Anlage says. “Whether or not it’s Majoranas on the surface is certainly a consequential issue, but it’s exploring novel physics which is the most exciting stuff.”

    See the full article here.

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Maryland Campus

    Driven by the pursuit of excellence, the University of Maryland (US) has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.

    The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.

    Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.

     
  • richardmitnick 10:33 am on June 19, 2021 Permalink | Reply
    Tags: "New research adds a wrinkle to our understanding of the origins of matter in the Milky Way", , , , CALET on the ISS from Japanese; American; and Italian teams., Cosmic rays arrive at Earth from elsewhere in the galaxy at a huge range of energies—anywhere from 1 billion volts to 100 billion billion volts., , University of Maryland (US)   

    From University of Maryland (US) via phys.org : “New research adds a wrinkle to our understanding of the origins of matter in the Milky Way” 

    From University of Maryland (US)

    via

    phys.org

    New findings published this week in Physical Review Letters suggest that carbon, oxygen, and hydrogen cosmic rays travel through the galaxy toward Earth in a similar way, but, surprisingly, that iron arrives at Earth differently. Learning more about how cosmic rays move through the galaxy helps address a fundamental, lingering question in astrophysics: How is matter generated and distributed across the universe?

    “So what does this finding mean?” asks John Krizmanic, a senior scientist with UMBC’s Center for Space Science and Technology (CSST). “These are indicators of something interesting happening. And what that something interesting is we’re going to have to see.”

    Cosmic rays are atomic nuclei—atoms stripped of their electrons—that are constantly whizzing through space at nearly the speed of light. They enter Earth’s atmosphere at extremely high energies. Information about these cosmic rays can give scientists clues about where they came from in the galaxy and what kind of event generated them.

    An instrument on the International Space Station (ISS) called the Calorimetric Electron Telescope (CALET) has been collecting data about cosmic rays since 2015.

    1
    CALET Overview CALorimetric Electron Telescope (CALET) is an astrophysics mission that searches for signatures of dark matter and provides the highest energy direct measurements of the cosmic ray electron spectrum in order to observe discrete sources of high energy particle acceleration in our local region of the Galaxy. Credit: National Aeronautics Space Agency (US), Japan Aerospace Exploration Agency [ (国立研究開発法人宇宙航空研究開発機構] (JP) JAXA, Italian Space Agency A.S.I. – [Agenzia Spaziale Italiana] (IT).

    The data include details such as how many and what kinds of atoms are arriving, and how much energy they’re arriving with. The American, Italian, and Japanese teams that manage CALET, including UMBC’s Krizmanic and postdoc Nick Cannady, collaborated on the new research.

    Iron on the move

    Cosmic rays arrive at Earth from elsewhere in the galaxy at a huge range of energies—anywhere from 1 billion volts to 100 billion billion volts. The CALET instrument is one of extremely few in space that is able to deliver fine detail about the cosmic rays it detects. A graph called a cosmic ray spectrum shows how many cosmic rays are arriving at the detector at each energy level. The spectra for carbon, oxygen, and hydrogen cosmic rays are very similar, but the key finding from the new paper is that the spectrum for iron is significantly different.

    There are several possibilities to explain the differences between iron and the three lighter elements. The cosmic rays could accelerate and travel through the galaxy differently, although scientists generally believe they understand the latter, Krizmanic says.

    “Something that needs to be emphasized is that the way the elements get from the sources to us is different, but it may be that the sources are different as well,” adds Michael Cherry, physics professor emeritus at Louisiana State University (LSU) (US) and a co-author on the new paper. Scientists generally believe that cosmic rays originate from exploding stars (supernovae), but neutron stars or very massive stars could be other potential sources.

    Next-level precision

    An instrument like CALET is important for answering questions about how cosmic rays accelerate and travel, and where they come from. Instruments on the ground or balloons flown high in Earth’s atmosphere were the main source of cosmic ray data in the past. But by the time cosmic rays reach those instruments, they have already interacted with Earth’s atmosphere and broken down into secondary particles. With Earth-based instruments, it is nearly impossible to identify precisely how many primary cosmic rays and which elements are arriving, plus their energies. But CALET, being on the ISS above the atmosphere, can measure the particles directly and distinguish individual elements precisely.

    Iron is a particularly useful element to analyze, explains Cannady, a postdoc with CSST and a former Ph.D. student with Cherry at LSU. On their way to Earth, cosmic rays can break down into secondary particles, and it can be hard to distinguish between original particles ejected from a source (like a supernova) and secondary particles. That complicates deductions about where the particles originally came from.

    “As things interact on their way to us, then you’ll get essentially conversions from one element to another,” Cannady says. “Iron is unique, in that being one of the heaviest things that can be synthesized in regular stellar evolution, we’re pretty certain that it is pretty much all primary cosmic rays. It’s the only pure primary cosmic ray, where with others you’ll have some secondary components feeding into that as well.”

    “Made of stardust”

    Measuring cosmic rays gives scientists a unique view into high-energy processes happening far, far away. The cosmic rays arriving at CALET represent “the stuff we’re made of. We are made of stardust,” Cherry says. “And energetic sources, things like supernovas, eject that material from their interiors, out into the galaxy, where it’s distributed, forms new planets, solar systems, and… us.”

    “The study of cosmic rays is the study of how the universe generates and distributes matter, and how that affects the evolution of the galaxy,” Krizmanic adds. “So really it’s studying the astrophysics of this engine we call the Milky Way that’s throwing all these elements around.”

    A global effort

    The Japanese space agency launched CALET and today leads the mission in collaboration with the U.S. and Italian teams. In the U.S., the CALET team includes researchers from LSU; NASA Goddard Space Flight Center (US); UMBC; University of Maryland, College Park; University of Denver (US); and Washington University.The new paper is the fifth from this highly successful international collaboration published in PRL, one of the most prestigious physics journals.

    CALET was optimized to detect cosmic ray electrons, because their spectrum can contain information about their sources. That’s especially true for sources that are relatively close to Earth in galactic terms: within less than one-thirtieth the distance across the Milky Way. But CALET also detects the atomic nuclei of cosmic rays very precisely. Now those nuclei are offering important insights about the sources of cosmic rays and how they got to Earth.

    “We didn’t expect that the nuclei—the carbon, oxygen, protons, iron—would really start showing some of these detailed differences that are clearly pointing at things we don’t know,” Cherry says.

    The latest finding creates more questions than it answers, emphasizing that there is still more to learn about how matter is generated and moves around the galaxy. “That’s a fundamental question: How do you make matter?” Krizmanic says. But, he adds, “That’s the whole point of why we went in this business, to try to understand more about how the universe works.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Maryland Campus

    Driven by the pursuit of excellence, the University of Maryland (US) has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.

    The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.

    Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.

     
  • richardmitnick 2:02 pm on April 20, 2021 Permalink | Reply
    Tags: , , The scientists developed a method to enhance receivers based on quantum physics properties to dramatically increase network performance while significantly reducing the error bit rate (EBR) and energy, University of Maryland (US)   

    From American Institute of Physics-AIP (US) via phys.org : “Boosting fiber optics communications with advanced quantum-enhanced receiver” 

    From American Institute of Physics-AIP (US)

    via

    phys.org

    April 20, 2021

    1
    Illustration showing how single-photon detection is used for feedback. Once correct parameters for the reference beam are established, the input state is extinguished. Credit: Ivan Burenkov.

    Fiber optic technology is the holy grail of high-speed, long-distance telecommunications. Still, with the continuing exponential growth of internet traffic, researchers are warning of a capacity crunch.

    In AVS Quantum Science, researchers from the National Institute of Standards and Technology (US) and the University of Maryland (US) show how quantum-enhanced receivers could play a critical role in addressing this challenge.

    The scientists developed a method to enhance receivers based on quantum physics properties to dramatically increase network performance while significantly reducing the error bit rate (EBR) and energy consumption.

    Fiber optic technology relies on receivers to detect optical signals and convert them into electrical signals. The conventional detection process, largely as a result of random light fluctuations, produces ‘shot noise,’ which decreases detection ability and increases EBR.

    To accommodate this problem, signals must continually be amplified as pulsating light becomes weaker along the optic cable, but there is a limit to maintaining adequate amplification when signals become barely perceptible.

    Quantum-enhanced receivers that process up to two bits of classical information and can overcome the shot noise have been demonstrated to improve detection accuracy in laboratory environments. In these and other quantum receivers, a separate reference beam with a single-photon detection feedback is used so the reference pulse eventually cancels out the input signal to eliminate the shot noise.

    The researchers’ enhanced receiver, however, can decode as many as four bits per pulse, because it does a better job in distinguishing among different input states.

    To accomplish more efficient detection, they developed a modulation method and implemented a feedback algorithm that takes advantage of the exact times of single photon detection. Still, no single measurement is perfect, but the new holistically designed communication system yields increasingly more accurate results on average.

    “We studied the theory of communications and the experimental techniques of quantum receivers to come up with a practical telecommunication protocol that takes maximal advantage of the quantum measurement,” author Sergey Polyakov said. “With our protocol, because we want the input signal to contain as few photons as possible, we maximize the chance that the reference pulse updates to the right state after the very first photon detection, so at the end of the measurement, the EBR is minimized.”

    See the full article here.

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The American Institute of Physics (AIP) promotes science and the profession of physics, publishes physics journals, and produces publications for scientific and engineering societies. The AIP is made up of various member societies. Its corporate headquarters are at the American Center for Physics in College Park, Maryland, but the institute also has offices in Melville, New York, and Beijing.

    The focus of the AIP appears to be organized around a set of core activities. The first delineated activity is to support member societies regarding essential society functions. This is accomplished by annually convening the various society officers to discuss common areas of concern. A range of topics is discussed which includes scientific publishing, public policy issues, membership-base issues, philanthropic giving, science education, science careers for a diverse population, and a forum for sharing ideas.

    Another core activity is publishing the science of physics in research journals, magazines, and conference proceedings. Member societies continue nevertheless to publish their own journals.

    Other core activities are tracking employment and education trends with six decades of coverage, being a liaison between research science and industry, historical collections and physics outreach programs, and supporting science education initiatives and supporting undergraduate physics. One other core activity is as an advocate for science policy to the U.S. Congress and the general public.

    Member societies:
    Acoustical Society of America
    American Association of Physicists in Medicine
    American Association of Physics Teachers
    American Astronomical Society
    American Crystallographic Association
    American Meteorological Society
    American Physical Society
    American Vacuum Society

    Affiliated societies

    American Association for the Advancement of Science, Section on Physics
    American Chemical Society, Division of Physical Chemistry
    American Institute of Aeronautics and Astronautics
    American Nuclear Society
    American Society of Civil Engineers
    ASM International
    Astronomical Society of the Pacific
    Biomedical Engineering Society
    Council on Undergraduate Research, Physics & Astronomy Division
    Electrochemical Society
    Geological Society of America
    IEEE Nuclear and Plasma Sciences Society
    International Association of Mathematical Physics
    International Union of Crystallography
    International Centre for Diffraction Data
    Health Physics Society

     
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