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  • richardmitnick 8:26 am on September 23, 2020 Permalink | Reply
    Tags: "I focus on how electrons behave within solids.", "Think We Already Know Everything About Electrons? Think Again", , , , Emergent phenomena-in which groups of atoms or electrons act in unexpected ways., Groups of electrons collectively behave differently than we would expect from the way each individual electron acts on its own., , Scanning tunneling microscopy (STM), , Songtian Sonia Zhang, Superconductivity is an example of an emergent phenomenon within physics., , Topological superconductors,   

    From Simons Foundation: Women in STEM-Songtian Sonia Zhang”Think We Already Know Everything About Electrons? Think Again” 

    From Simons Foundation

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    Songtian Sonia Zhang. Credit: Rick Soden, Princeton University
    Physicist Songtian Sonia Zhang explores how electrons work within the tiniest objects and finds that they sometimes do unexpected things.

    September 22, 2020
    Marcus Banks

    Songtian Sonia Zhang envisioned a life in finance, until she discovered that learning how electrons work is much more rewarding. A fundamental physicist with a bachelor’s degree from the University of Waterloo in Ontario, Canada, and a doctorate from Princeton University, Zhang has already discovered unexpected behaviors among electrons found in quantum materials like superconductors or magnets. But many mysteries remain about the behavior of these tiny particles. Now beginning a postdoctoral appointment at Columbia University in the physics lab of Dmitri N. Basov, Zhang already has lots of ideas about what she wants to explore next. Our conversation has been edited for clarity.

    You began as a dual major in economics and physics at the University of Waterloo. What prompted the sharper focus on physics instead?

    When I was an undergraduate at Waterloo, I planned to pursue a career in finance, perhaps even on Wall Street. I was interested in physics too, but I never imagined becoming a physicist. That all changed after I completed a physics research project in my third year of college, which happened to overlap with my first job at a financial services firm. This gave me the chance to directly compare finance to physics work — and physics won out handily.

    When I was doing physics, I felt like I was helping to bring new understanding into the world. I know that sounds corny, but it’s true. And it was far more rewarding to me than my work at the financial firm, where I essentially was moving money around. Don’t get me wrong, we need money! But I knew early that physics was for me.

    That sounds clarifying! But the study of physics is broad. How did you narrow your interests?

    During my last semester at Waterloo I researched a special kind of magnet known as ‘spin ice,’ in which the atoms are arranged in a complex lattice pattern. Most magnets have a north and south pole. And if you cut a magnet in two, each new magnet will then also have a north and south pole. But spin ice magnets have such a complex structure that we call them geometrically frustrated. Spin ice magnets can behave like monopoles — that is, a magnet with only one pole instead of the normal two. We still don’t know if monopoles even exist! But the spin ice magnet I studied sure seemed like a monopole, which was fascinating to me. When I first began to study physics, I assumed I would become an astrophysicist. Instead I decided to be more down-to-earth — literally. Today I study the physics of solids, not stars.

    This sounds like quantum physics.

    In many ways, yes. But quantum physics is an extremely broad term that can apply to many things, so in some ways it’s too general. The specific field I work in is condensed matter physics. I focus on how electrons behave within solids. I’m particularly interested in how groups of electrons behave, and especially how their collective behavior cannot be predicted by how each individual in the group acts.

    You’re saying that groups of electrons collectively behave differently than we would expect from the way each individual electron acts on its own?

    Exactly. We call this overall concept ‘emergent phenomena,’ in which groups of atoms or electrons act in unexpected ways. There are many examples of emergent phenomena in nature that go well beyond quantum physics. Think of individual birds migrating together as a cohesive flock, or a school of fish swimming upriver to spawn. Even though each individual bird or fish moves independently, they become entangled in the group and impossible to distinguish from one another.

    Superconductivity is an example of an emergent phenomenon within physics. Regular electrical conductors carry a current known as electricity; this is how we light lightbulbs, for example, by connecting an electricity source to an object that emits light. These kinds of everyday conductors come with inherent inefficiencies — energy is always lost because the electricity faces resistance as it travels. This is why lightbulbs eventually burn out.

    In contrast, a superconductor operating in extremely low temperatures (−450 F) can keep conducting electricity forever, because the electricity meets no resistance at all. Nobody could have predicted that superconductors could do this. It had to be discovered through observation, and it’s an example of how we are constantly learning about new types of emergent phenomena. Sometimes this is purely about developing knowledge for its own sake, but oftentimes this work has practical applications.

    We’ll loop back to the practical applications in a moment. First, though, what was your most exciting discovery at Princeton?

    At Princeton I studied kagome magnets. The atoms that comprise these magnets are arranged in a lattice which evokes the famous Japanese basket lattice pattern of the same name.

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    Scanning tunneling microscopy (STM) image of magnetic adatoms deposited on topological superconductor candidate PbTaSe2. Inset: a 2D enlarged view. Each magnetic adatom can host a Majorana zero mode acting as a topological qubit which has the potential to be used for robust quantum computation. Credit: Songtian Zhang.

    Like the spin ice magnets I previously mentioned, kagome magnets are geometrically frustrated. In our research, we did various things to these magnets, such as observing them within magnetic fields of various strengths or alternating their temperatures. This was all to see how the electrons behaved in different conditions. In high magnetic fields the kagome magnets started acting like negative magnets — meaning they exerted more energy when moving in the same direction as a magnetic field and not when going ‘against the wind,’ so to speak.

    We published these unexpected results in Nature Physics last year.

    The fact that we discovered something totally unexpected shows the importance of keeping an open mind, of not being locked into any one idea. Instead, we are always finding new questions to ask.

    As you begin your postdoctoral work at Columbia, what do you plan to focus on, at least initially, until you discover new questions?

    I’m interested in learning more about topological insulators: objects that, on the surface, conduct electricity but in their interior act as an insulator. When the material is cut, the new surface, which was previously the insulating bulk, becomes conductive and can now support surface currents. Besides topological insulators there are topological superconductors, which can superconduct currents of electricity. The physics community has made some headway in understanding these superconductors, but there’s a lot more work that needs to be done.

    And how do you hope this knowledge will inform our understanding of the natural and physical world?

    Topological superconductors come from the math concept of topology. A good way to think about topology is the relationship between a doughnut, with a hole in the middle, and a ball, which has no holes. In this comparison, the doughnut and the ball are topologically distinct.

    By comparison, the doughnut would be topologically identical to a ring, which also has a hole in the middle. In this example, the number of holes is a topological property that can’t be destroyed without changing the underlying nature of the object.

    In physics, we’re interested in electronic behaviors that are similarly robust, such as in topological superconductors. There’s great potential for topological superconductors to be used for powerful, reliable and robust quantum computation, which will be a giant leap past the computers we use today. I can’t say exactly how my work will contribute to this, but I do know I’m excited to be on the journey. And I know I will enjoy it more than working on Wall Street.

    See the full article here.

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    Please help promote STEM in your local schools.

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    Mission and Model

    The Simons Foundation’s mission is to advance the frontiers of research in mathematics and the basic sciences.

    Co-founded in New York City by Jim and Marilyn Simons, the foundation exists to support basic — or discovery-driven — scientific research undertaken in the pursuit of understanding the phenomena of our world.

    The Simons Foundation’s support of science takes two forms: We support research by making grants to individual investigators and their projects through academic institutions, and, with the launch of the Flatiron Institute in 2016, we now conduct scientific research in-house, supporting teams of top computational scientists.

     
  • richardmitnick 8:59 am on July 30, 2019 Permalink | Reply
    Tags: A team of physicists at University of Illinois at Chicago and the University of Hamburg have taken a different approach., Entangled Majorana quasiparticles produced by splitting an electron into two halves are surprisingly stable., , , Majorana quasiparticles, , , , , , , They remember how they've been moved around a property that could be exploited for storing information., They've started with a rhenium superconductor a material that conducts electricity with zero resistance when supercooled to around 6 Kelvin (–267°C; 449°F)., Topological superconductors, ,   

    From University of Illinois and U Hamburg, via Science Alert: “An Elusive Particle That Acts as Its Own Antiparticle Has Just Been Imaged” 

    U Illinois bloc

    From University of Illinois Chicago

    and

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    U Hamburg

    via

    30 JULY 2019
    MICHELLE STARR

    3
    (Palacio-Morales et al. Science Advances, 2019)

    New images of the Majorana fermion have brought physicists a step closer to harnessing the mysterious objects for quantum computing.

    These strange objects – particles that acts as their own antiparticles – have a vast as-yet untapped potential to act as qubits, the quantum bits that are the basic units of information in a quantum computer.

    IBM iconic image of Quantum computer

    They’re equivalent to binary bits in a traditional computer. But, where regular bits can represent a 1 or a 0, qubits can be either 1, 0 or both at the same time, a state known as quantum superposition. Quantum superposition is actually pretty hard to maintain, although we’re getting better at it.

    This is where Majorana quasiparticles come in. These are excitations in the collective behaviour of electrons that act like Majorana fermions, and they have a number of properties that make them an attractive candidate for qubits.

    Normally, a particle and an antiparticle will annihilate each other, but entangled Majorana quasiparticles produced by splitting an electron into two halves are surprisingly stable. In addition, they remember how they’ve been moved around, a property that could be exploited for storing information.

    But the quasiparticles have to remain separated by a sufficient distance. This can be done with a special nanowire, but a team of physicists at the University of Illinois at Chicago and the University of Hamburg in Germany have taken a different approach.

    They’ve started with a rhenium superconductor, a material that conducts electricity with zero resistance when supercooled to around 6 Kelvin (–267°C; 449°F).

    On top of these superconductors, the researchers deposited nanoscale islands of single layers of magnetic iron atoms. This creates what is known as a topological superconductor – that is, a superconductor that contains a topological knot.

    “This topological knot is similar to the hole in a donut,” explained physicist Dirk Morr of the University of Illinois at Chicago.

    “You can deform the donut into a coffee mug without losing the hole, but if you want to destroy the hole, you have to do something pretty dramatic, such as eating the donut.”

    When electrons flow through the superconductor, the team predicted that Majorana fermions would appear in a one-dimensional mode at the edges of the iron islands – around the so-called donut hole. And that by using a scanning tunneling microscope – an instrument used for imaging surfaces at the atomic level – they would see this visualised as a bright line.

    Sure enough, a bright line showed up.

    It’s not the first time Majorana fermions have been imaged, but it does represent a step forward. And just last month, a different team of researchers revealed that they had been able to turn Majorana quasiparticles on and off.

    But being able to visualise these particles, the researchers said, brings us closer to using them as qubits.

    “The next step will be to figure out how we can quantum engineer these Majorana qubits on quantum chips and manipulate them to obtain an exponential increase in our computing power,” Morr said.

    The research has been published in Science Advances.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

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    The University

    Universität Hamburg is the largest institution for research and education in northern Germany. As one of the country’s largest universities, we offer a diverse range of degree programs and excellent research opportunities. The University boasts numerous interdisciplinary projects in a broad range of fields and an extensive partner network of leading regional, national, and international higher education and research institutions.
    Sustainable science and scholarship

    Universität Hamburg is committed to sustainability. All our faculties have taken great strides towards sustainability in both research and teaching.
    Excellent research

    As part of the Excellence Strategy of the Federal and State Governments, Universität Hamburg has been granted clusters of excellence for 4 core research areas: Advanced Imaging of Matter (photon and nanosciences), Climate, Climatic Change, and Society (CliCCS) (climate research), Understanding Written Artefacts (manuscript research) and Quantum Universe (mathematics, particle physics, astrophysics, and cosmology).

    An equally important core research area is Infection Research, in which researchers investigate the structure, dynamics, and mechanisms of infection processes to promote the development of new treatment methods and therapies.
    Outstanding variety: over 170 degree programs

    Universität Hamburg offers approximately 170 degree programs within its eight faculties:

    Faculty of Law
    Faculty of Business, Economics and Social Sciences
    Faculty of Medicine
    Faculty of Education
    Faculty of Mathematics, Informatics and Natural Sciences
    Faculty of Psychology and Human Movement Science
    Faculty of Business Administration (Hamburg Business School).

    Universität Hamburg is also home to several museums and collections, such as the Zoological Museum, the Herbarium Hamburgense, the Geological-Paleontological Museum, the Loki Schmidt Garden, and the Hamburg Observatory.
    History

    Universität Hamburg was founded in 1919 by local citizens. Important founding figures include Senator Werner von Melle and the merchant Edmund Siemers. Nobel Prize winners such as the physicists Otto Stern, Wolfgang Pauli, and Isidor Rabi taught and researched at the University. Many other distinguished scholars, such as Ernst Cassirer, Erwin Panofsky, Aby Warburg, William Stern, Agathe Lasch, Magdalene Schoch, Emil Artin, Ralf Dahrendorf, and Carl Friedrich von Weizsäcker, also worked here.
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    U Illinois campus

    The University of Illinois at Urbana-Champaign community of students, scholars, and alumni is changing the world.

    With our land-grant heritage as a foundation, we pioneer innovative research that tackles global problems and expands the human experience. Our transformative learning experiences, in and out of the classroom, are designed to produce alumni who desire to make a significant, societal impact.

    The University of Illinois at Chicago (UIC) is a public research university in Chicago, Illinois. Its campus is in the Near West Side community area, adjacent to the Chicago Loop. The second campus established under the University of Illinois system, UIC is also the largest university in the Chicago area, having approximately 30,000 students[9] enrolled in 15 colleges.

    UIC operates the largest medical school in the United States with research expenditures exceeding $412 million and consistently ranks in the top 50 U.S. institutions for research expenditures.[10][11][12] In the 2019 U.S. News & World Report’s ranking of colleges and universities, UIC ranked as the 129th best in the “national universities” category.[13] The 2015 Times Higher Education World University Rankings ranked UIC as the 18th best in the world among universities less than 50 years old.[14]

    UIC competes in NCAA Division I Horizon League as the UIC Flames in sports. The Credit Union 1 Arena (formerly UIC Pavilion) is the Flames’ venue for home games.

     
  • richardmitnick 10:41 am on February 19, 2018 Permalink | Reply
    Tags: , , , , , Topological superconductors   

    From phys.org: “Unconventional superconductor may be used to create quantum computers of the future” 

    physdotorg
    phys.org

    February 19, 2018

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    After an intensive period of analyses the research team led by Professor Floriana Lombardi, Chalmers University of Technology, was able to establish that they had probably succeeded in creating a topological superconductor. Credit: Johan Bodell/Chalmers University of Technology

    With their insensitivity to decoherence, Majorana particles could become stable building blocks of quantum computers. The problem is that they only occur under very special circumstances. Now, researchers at Chalmers University of Technology have succeeded in manufacturing a component that is able to host the sought-after particles.

    Researchers throughout the world are struggling to build quantum computers. One of the great challenges is to overcome the sensitivity of quantum systems to decoherence, the collapse of superpositions. One track within quantum computer research is therefore to make use of Majorana particles, which are also called Majorana fermions. Microsoft, among other organizations, is exploring this type of quantum computer.

    Majorana fermions are highly original particles, quite unlike those that make up the materials around us. In highly simplified terms, they can be seen as half-electron. In a quantum computer, the idea is to encode information in a pair of Majorana fermions separated in the material, which should, in principle, make the calculations immune to decoherence.

    So where do you find Majorana fermions? In solid state materials, they only appear to occur in what are known as topological superconductors. But a research team at Chalmers University of Technology is now among the first in the world to report that they have actually manufactured a topological superconductor.

    “Our experimental results are consistent with topological superconductivity,” says Floriana Lombardi, professor at the Quantum Device Physics Laboratory at Chalmers.

    To create their unconventional superconductor, they started with what is called a topological insulator made of bismuth telluride, Be2Te3. A topological insulator conducts current in a very special way on the surface. The researchers placed a layer of aluminum, a conventional superconductor, on top, which conducts current entirely without resistance at low temperatures.

    “The superconducting pair of electrons then leak into the topological insulator, which also becomes superconducting,” explains Thilo Bauch, associate professor in quantum device physics.

    However, the initial measurements all indicated that they only had standard superconductivity induced in the Bi2Te3 topological insulator. But when they cooled the component down again later, to routinely repeat some measurements, the situation suddenly changed—the characteristics of the superconducting pairs of electrons varied in different directions.

    “And that isn’t compatible at all with conventional superconductivity. Unexpected and exciting things occurred,” says Lombardi.

    “For practical applications, the material is mainly of interest to those attempting to build a topological quantum computer. We want to explore the new physics hidden in topological superconductors—this is a new chapter in physics,” Lombardi says.

    The results were recently published in Nature Communications in a study titled “Induced unconventional superconductivity on the surface states of Bi2Te3 topological insulator.”

    See the full article here .

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
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