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Events on Thursday, October 26th, 2023

R. G. Herb Condensed Matter Seminar
First-Principles Many-Body Theory and Quantum Dynamics for Solid-State Materials
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Yuan Ping, UW-Madison
Abstract: Stable, scalable, and reliable quantum information science (QIS) is poised to revolutionize human well-being through quantum computation, communication and sensing. In this talk, I will show our recent development on first-principles computational platforms to study quantum coherence and optical readout as critical processes in QIS and spintronics in solid-state materials, by combining first-principles many-body theory and open quantum dynamics.

First, we will show how we reliably predict energetics, electronic and optical properties of spin defects and their host two-dimensional materials from first-principles many-body theory, which accurately describes highly anisotropic dielectric screening and strong many-body interactions. In particular, we will show how we predict spin-dependent optical contrast for information readout of spin qubits by computing exciton radiative and phonon-assisted nonradiative as well as spin-orbit induced intersystem crossing rates from first-principles.

Next, we will introduce our recently developed real-time density-matrix dynamics approach with first-principles electron-electron, electron-phonon, electron-impurity scatterings and self-consistent spin-orbit coupling, which can accurately predict spin and carrier lifetime and pump-probe Kerr-rotation signatures for general solids. As an example, we will show our theoretical prediction on Dirac materials under electric field to realize spin-valley locking with extremely long spin lifetime and spin diffusion length, and distinct dependence on electron-phonon couplings in spin and carrier relaxation in halide perovskites. This theoretical and computational development is critical for designing new materials promising in quantum-information science and spintronics applications.
Host: Alex Levchenko
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Astronomy Colloquium
Cosmic ray electron re-acceleration in the intracluster medium via magnetic pumping
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Aaron Tran, UW-Madison
Abstract: Clusters of galaxies are embedded in a hot (T~10^7 K), low-density halo of gas called the intracluster medium (ICM).  In some clusters, the ICM hosts low-frequency (MHz–GHz) radio synchrotron emission associated with radio galaxies, jets, and cluster merger-induced shocks and turbulence.  The radio emission comes from GeV cosmic ray electrons (CRe).  Some CRe may be "fossils", i.e., previously-accelerated CRe that then radiated and cooled to long-lived MeV energies.  Fossil CRe are invisible until some perturbation, like adiabatic compression or turbulence, re-accelerates the CRe back to GeV energies.  I will present a recent study of CRe re-acceleration via magnetic pumping, a mechanism in which small-scale (nanoparsec) plasma waves coupled to large-scale (kiloparsec to Megaparsec) motions can efficiently energize CRe.  In 1D kinetic plasma simulations, we show that ion cyclotron wave scattering with background compression leads to resonant CRe gaining ~10-30% of their initial energy in one compress/expand cycle, assuming adiabatic expansion without further scattering.  I will comment briefly on the applicability and limitations of this re-acceleration mechanism, and on prospects for future work.
Host: Ke Zhang
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