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Light-Cone Effects after Quantum Quenches and Excitations at Finite Entropy

Fabian Essler, Oxford University

04.07.2014 at 10:15 

Signal propagation in the non equilibirum evolution after quantum quenches has recently attracted much experimental and theoretical interest. A key question arising in this context is what principles, and which of the properties of the quench, determine the characteristic propagation velocity.
I discuss such issues for a class of quench protocols in one of the central paradigms of interacting many-particle quantum systems, the spin-1/2 Heisenberg XXZ chain. I consider quenches from a variety of initial thermal density matrices to the same final Hamiltonian. The spreading velocities are observed to vary substantially with the initial density matrix. However, a striking data collapse is achieved when the spreading velocity is considered to be a function of the excess energy. Using the fact that the XXZ chain is integrable, I present an explanation of the observed velocities in terms of ''excitations'' in an appropriately defined generalized Gibbs ensemble.

 

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