CQOM-Seminar - Michael Gullans: "Entanglement structure of current driven quantum many-body systems"
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Entanglement structure of current driven quantum many-body systems.
Michael Gullans, Princeton University
When an extended system is coupled at its opposite boundaries to two reservoirs at different temperatures or chemical potentials, it cannot achieve a global thermal equilibrium and is instead driven to a set of current carrying non-equilibrium states. Motivated by developments in the understanding of thermalization in closed quantum many-body systems, we find conditions under which such current-driven systems can achieve, or violate, local thermal equilibrium by investigating their entropy, mutual information, and entanglement at long times. We focus on a specific model consisting of a two-parameter family of random unitary circuits acting locally on a chain of spin-1/2s (equivalently, qubits) that exhibits quantum chaotic behavior in most of its parameter space. The only conserved quantity is the total magnetization of the spins. We choose the model so that for all parameter values the time-averaged correlation functions agree and are close to local equilibrium. However, computing the total von Neumann entropy of the system shows that there are in fact three distinct "phases" of the driven problem, with local equilibrium only emerging in the quantum chaotic regime, while one of the other phases exhibits volume-law mutual information and entanglement. We extend these results to the three-dimensional, non-interacting Anderson model in the diffusive regime, showing that the non-equilibrium steady-state for fermions realizes the volume-law mutual information phase of the random circuit. Our results suggest a generic picture for the emergence of local equilibrium in current-driven quantum chaotic systems, as well as provide insights into methods to stabilize highly-entangled many-body states out of equilibrium.
Coffee and cake will be served from 13:00