Special QM Seminar Speaker Joaquin Rodriguez Nieva (Harvard) Thursday, May 23

Time: 11:00 am
Venue: 325 LeConte
Title: Probing hydrodynamics and thermalization in quantum spin systems
Abstract: The presence of symmetries and conservation laws can have striking manifestations in the dynamic and thermalization behavior of interacting quantum systems. I will discuss two such manifestations arising in the context of ferromagnets driven out of equilibrium when SU(2) symmetry is present, and I will propose experiments to observe these behaviors. First, I will show that ferromagnets can enter the hydrodynamic regime when the magnon density is large. A key fingerprint of this regime is the existence of a sound mode which governs dynamics at small frequencies and is manifested as a gapless excitation of the longitudinal spin component even in the presence of a Zeeman gap. Such mode can be accessed with recently-introduced spin qubit magnetometers, which are ideally suited to probe dynamics in quantum spin systems. Second, I will describe thermalization dynamics when ferromagnets are pumped into a non-thermal incoherent state. Despite being far from equilibrium, thermalization can nonetheless exhibit universal features, namely, universal scaling in time and momentum of quasiparticle occupation numbers. These two predictions, if experimentally confirmed, can inspire new platforms to explore hydrodynamics and thermalization in readily-available ferromagnetic materials, for instance Yttrium-Iron-Garnet (YIG)

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