Special QM Seminar Speaker Matteo Ippoliti (Stanford & UT Austin) Thursday, June 16 at 1:00 pm Pacific Time

Time/Venue Thursday, June 16 at 1:00 pm Pacific Time in Physics North 375 and via Zoom:

Meeting ID: 995 2349 9113 Passcode: 600704
Host Ehud Altman
Title Universal randomness beyond thermalization in quantum dynamics
Abstract Isolated quantum systems can achieve thermal equilibrium by generating entanglement between their degrees of freedom. As a result, local subsystems can be described by universal (equilibrium) ensembles of states that correctly reproduce thermal expectation values. Present-day quantum simulators, however, give us access to a much richer picture of quantum dynamics, comprising not just expectation values but also individual microscopic snapshots of the many-body state. This motivates the introduction of finer notions of quantum thermalization, based not only on expectation values but also on higher statistical moments that may be extracted from such snapshots. Recently, this idea was made concrete via the “projected ensemble”—the set of states on a subsystem obtained by projectively measuring its complement. Under chaotic dynamics at infinite temperature, this ensemble matches increasingly higher moments of the uniform distribution on the Hilbert space, i.e. it forms an approximate “quantum state k-design”. These criteria, one for each statistical moment k, define a hierarchy of time scales (the “design times”) beyond the thermalization time, recovered for k=1. Not much is known about the scaling of higher design times in general. I will review previous results and present recent work [1] in which we make progress on this question for (1+1)-dimensional quantum circuits by establishing a connection to measurement-induced entanglement phases.
[1] MI and Wen Wei Ho, arXiv:2204.13657

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