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Events on Thursday, April 12th, 2018

R. G. Herb Condensed Matter Seminar
Photonic analogues of topological superconductors
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Aashish Clerk, McGill University
Interest continues to grow in photonic and phononic analogues of topological electronic phases. In most cases, these systems are non-interacting, and have the same band structure and edge state structure as their fermionic counterparts. In this talk, I’ll discuss recent theory work in my group showing how parametric “two-photon” driving can be used to realize a new class of photonic topological systems that superficially resemble topological superconductors. Unlike standard particle-number conserving models of non-interacting topological phases, these new systems exhibit crucial differences between their bosonic and fermionic versions. Further, one can realize a situation where all bulk states are stable, but where edge states are guaranteed to be unstable. Such a system can form the basis of a useful device: a topologically-protected amplifier which operates close to the fundamental limits set by quantum mechanics. I’ll discuss how these ideas could be realized in a variety of different experimental platforms, including superconducting quantum circuits and optomechanics.
Host: Vavilov
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Astronomy Colloquium
MHD turbulence in the interstellar medium
Time: 3:30 pm - 5:00 pm
Place: 4421 Sterling Hall, Coffee and Cookies at 3:30 PM. Talk begins at 3:45 PM
Speaker: Siyao XU, Hubble Fellow UW Astronomy Dept
Abstract: Turbulence and magnetic fields are ubiquitous in the Universe. Magnetohydrodynamic (MHD) turbulence is important for all branches of astrophysics involving gas dynamics. The developments of turbulence theories bring a paradigm shift in many fields of astronomy. I will start from an introduction of modern theories of MHD turbulence and then show some examples for their general applicability in understanding important physical processes in the interstellar medium (ISM), including the formation of density filaments commonly seen in both the diffuse ISM and dense molecular clouds, and the interstellar scattering of Galactic pulsars.<br>
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