Physics Colloquium

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Now showing 1 - 10 of 103
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    Compact Penning Traps for Quantum Science with Cold Atomic Ions
    (Georgia Institute of Technology, 2022-04-11) Sawyer, Brian C.
    Penning ion traps are useful experimental platforms for quantum simulation, mass spectrometry, precision metrology, and molecular ion spectroscopy. The GTRI Quantum Systems Division (QSD) has developed a compact, permanent-magnet-based Penning trap that is compatible with cold ion experiments, and we have recently updated our compact trap design with printed-circuit-board electrodes and improved trap magnetic field stability. We describe some near-term applications of this system including compact atomic clocks with dual-species, three-dimensional (3D) ion crystals and demonstration of the quantum approximate optimization algorithm (QAOA) with 2D ion arrays. We also highlight other notable results from the QSD in the field of ion trap quantum information.
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    Opportunities Created by Spin-Orbit Interactions
    (Georgia Institute of Technology, 2022-04-04) Cao, Gang
    Effects of spin-orbit interactions in condensed matter are an important and rapidly evolving topic. A sea change occurred with the discovery of spin-orbit interactions in graphene by Mele and Kane, which has led to the exciting new field of physics addressing a rare interplay between spin-orbit and Coulomb interactions in condensed matter. I will describe an entirely new hierarchy of energy scales inherent in 4d- and 5d-electron based oxides and its unique consequences, highlighting discrepancies between experimental confirmation and theoretical proposals that address superconducting, topological and quantum spin liquid phases in iridates. I will then present our recent discoveries of novel quantum phenomena in iridates and ruthenates and conclude by venturing a perspective for research on spin-orbit-coupled oxides [1,2]. References: 1. Physics of Spin-Orbit-Coupled Oxides, Gang Cao and Lance E. De Long, Oxford University Press; Oxford, 2021 2. The Challenge of Spin-Orbit-Tuned Ground States in Iridates: A Key Issues Review, Gang Cao and Pedro Schlottmann, Reports on Progress in Physics, 81 042502 (2018)
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    Optical Lattice Clocks: From Timekeepers to Spies of the Quantum Realm
    (Georgia Institute of Technology, 2022-03-28) Rey, Ana Maria
    Harnessing the behavior of complex systems is at the heart of quantum technologies. Precisely engineered ultracold gases are emerging as a powerful tool for this task. In this talk I will explain how ultracold strontium atoms trapped by light can be used to create optical lattice clocks – the most precise timekeepers ever imagined. I am going to explain why these clocks are not only fascinating, but of crucial importance since they can help us to answer cutting-edge questions about complex many-body phenomena and magnetism, to unravel big mysteries of our universe and to build the next generation of quantum technologies.
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    Protecting the Space Environment: Sustainability and Security
    (Georgia Institute of Technology, 2022-03-07) Borowitz, Mariel
    In recent years, the number of objects in space has grown rapidly, and this growth is projected to continue to accelerate over the next decade. There has also been increased military activity in space, including rendezvous and proximity operations and debris-creating anti-satellite tests. These trends pose risks to the sustainability and security of the space environment – risks that have the potential to negatively affect all space users, including those in the astronomy and astrophysics communities. In many cases, addressing these issues requires international coordination and cooperation. This talk reviews some of the current challenges and risks to the space environment and discusses ongoing efforts to develop international policy solutions.
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    Just Enough Entanglement: Simulating Quantum Systems without a Quantum Computer
    (Georgia Institute of Technology, 2021-12-06) White, Steven R.
    The general solution of many-particle quantum systems is exponentially complex, requiring a quantum computer to solve. But for many of the most important properties of realistic experimental systems, the exponential complexity is avoidable, because while the entanglement of the system is high enough to make the system interesting, it is much lower than quantum mechanics allows. Tensor network methods exploit this low entanglement to enable simulations of many quantum systems on an ordinary computer. In this talk, I will give an overview of these ideas and methods and then detail our recent progress in simulating high temperature superconductors, systems with exotic entangled states which we are increasingly able to understand through simulation.
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    Physics of Morphogenetic Matter
    (Georgia Institute of Technology, 2021-11-08) Gardel, Margaret
    My lab studies how the movement and shape of living cells is controlled by living materials constructed by protein assemblies within the cell interior. In this talk, I will describe my lab’s recent efforts to understand the design principles of the active, soft materials that drive morphogenesis of epithelial tissue. In particular, we are interested in the design principles by which protein-based materials generate, relax, sense and adapt to mechanical force. Here I will describe our current experimental efforts to study the regulation of the shape and size of epithelial cells. If time allows, I will discuss how physical constraints govern cell size regulation in epithelial tissue.
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    Crackdown on Academic Collaboration with China Harms American Science
    (Georgia Institute of Technology, 2021-11-01) Xi, Xiaoxing
    Academic collaboration with China was once encouraged by the US government and universities. As tension between the two countries rises rapidly, those who did, especially scientists of Chinese descent, are under heightened scrutiny by the federal government. Law enforcement officials consider collaborating with Chinese colleagues “by definition conveying sensitive information to the Chinese.” In 2015, I became a casualty of this campaign despite being innocent. “China Initiative” established by the Justice Department in 2018 has resulted in numerous prosecutions of university professors for alleged failure to disclose China ties. In this talk, I argue that academic decoupling is not in America’s interest. It is a tall order to convince the public and policy makers of this fact, but the scientific community must try lest the American leadership in science and technology will be irreparably damaged.
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    The Beginning of the Quantum Era
    (Georgia Institute of Technology, 2021-10-25) Shifman, Mikhail
    Shifman reviews the growth of quantum physics from its inception in the beginning of the 20th century to its maturity 50 years later. His narrative includes dramatic stories of the quantum pioneers between two wars. Caught between two evil regimes –– those of the National Socialist German Workers’ Party (known as Nazis) and the SU Communist Party (known as Bolsheviks) –– they had to make difficult choices in pursuing their scientific goals and aspirations.
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    Collapse of the Collapse: Physicists Return to Reality
    (Georgia Institute of Technology, 2021-10-18) Daw, Murray S.
    Recent developments[1] have shown that the collapse hypothesis is self-inconsistent and is no longer a viable theory. (The collapse hypothesis in quantum mechanics is that the state of a system is collapsed by a measurement, by some process of unknown character.) Based on earlier work by Ballentine[2] on the Ensemble Interpretation (in spite of the familiar-sounding name, this is almost entirely unknown), more recent work[3] has filled it out and demonstrated clearly that it provides a simple and natural resolution to the problem of measurement in quantum mechanics. We discuss the Ensemble Interpretation and recent developments, measurement theory in quantum mechanics (correcting many common misconceptions), and the resolutions of the Schrödinger Cat experiment, Wigner’s Friend experiment, and the Extended Wigner’s Friend experiment. Given that almost all current QM textbooks are based on the now defunct collapse hypothesis[4], we encourage switching to textbooks based on the Ensemble Interpretation[5] as a means of restoring consistency to QM. [1] D. Frauchiger & R. Renner, “Quantum theory cannot consistently describe the use of itself”, Nature Comm [2018] [2] L. Ballentine, “The statistical interpretation of quantum mechanics”, Rev Mod Phys [1970] [3] A. Rizzi, “How the natural interpretation of QM avoids the recent no-go theorem” Foundations of Physics [2020] and “A simple approach to measurement in quantum mechanics” arXiv [2020] [4] Two common examples include Griffiths and Morrison. Even though both discuss the use of ensembles, the statistical understanding is undermined completely by use of the collapse hypothesis in discussing measurements. [5] See L. Ballentine, “Quantum Mechanics” and A. Rizzi, “Physics for Realists: Quantum Mechanics”. (Several of the references in this talk are easily available here:
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    A tale of two motilities: adaptive biomechanical systems in complex, changing environments
    (Georgia Institute of Technology, 2021-09-27) Nirody, Jasmine
    Natural environments are heterogeneous and can fluctuate with time. As such, biomechanical systems from proteins to whole organisms have developed strategies to deal with considerable spatial and temporal variability. Understanding the physics behind these strategies is important both in an evolutionary context and for the development of bioinspired systems. I will discuss two (quite different!) broadly successful locomotive modes: flagellated motility in bacteria and interfacial locomotion in geckos. (1) A bacterium's life can be complicated: it must swim through fluids of varying viscosity as well as interact with surfaces and other bacteria. We characterized the mechanosensitive adaptation in bacterial flagella that facilitates these transitions by using magnetic tweezers to manipulate external torque on the bacterial flagellar motor. Our model for the dynamics of load-dependent assembly in the flagellar motor illustrates how this nanomachine allows bacteria to adapt to changes in their surroundings. (2) Animals that live in areas with periodic flooding must deal with seasonal fluctuations in their habitats. In the field, we showed that tropical geckos can run across the water’s surface as fast as they can on land. In the lab, we showed that these geckos use both surface slapping and surface tension, as well as take advantage of their superhydrophobic skin, to transition between terrestrial and semi-aquatic locomotion.