Special QM Seminar Speaker Sam Garratt (Oxford) Wednesday, October 21, 10:15 am

Host Ehud Altman
Time/Venue Wednesday, October 21, 10:15 am Pacific Time via Zoom
Talk Title: Many-body quantum chaos and the local pairing of Feynman histories
Abstract I will discuss many-body quantum dynamics under random Floquet circuits, simple examples of systems with local interactions that support ergodic phases. Quite generally, physical properties can be expressed in terms of multiple sums over Feynman histories, which for these models are paths or many-body orbits in Fock space. A natural simplification of such sums is the diagonal approximation, where the only terms that are retained are ones in which each path is paired with a partner that carries the complex conjugate weight. Our central result is to show how the diagonal approximation must be extended in many-body systems with local interactions. This leads to deviations of spectral statistics from random matrix theory, and of matrix element correlations from the eigenstate thermalisation hypothesis. Strikingly, both kinds of deviation diverge with system size. If there is time, I will also discuss the connection to the entanglement membrane, known to characterise the scrambling of quantum information.

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