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Quantum quenches in Integrable Models and the Generalised Gibbs Ensemble

by Dr. Spyros Sotiriadis (Universita' di Pisa e SISSA)

Dec 03, 2014 from 03:00 PM to 04:30 PM

Where Aula Teorici, via Irnerio 46

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Abstract:

When a closed system is set up in an arbitrary initial state, it is expected, based on the statistical principle of entropy maximisation under the constraint of energy conservation, to tend to thermal equilibrium. This is not the case for one-dimensional quantum integrable systems, since the existence of an infinite number of local conserved charges imposes to the time evolution additional constraints, which prevent thermalisation. In this case one may expect that the system equilibrates to a Generalised Gibbs Ensemble that incorporates all additional constraints. This conjecture turns out to be correct for a large class of physical problems called Quantum Quenches, which describe instantaneous changes in the parameters of a system that bring it out-of-equilibrium. We will review the attempts to prove this conjecture and to understand how such a statistically justified scenario emerges from the quantum mechanical physical laws. We will also discuss its (recently observed) failure in certain cases and the alleged connection of this failure to the (also recently discovered) quasi-local charges of integrable models.