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.
Here we investigate 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. We consider quenches from a variety of initial thermal
density matrices to the same final Hamiltonian using matrix product state
methods. The spreading velocities are observed to vary substantially with the
initial density matrix. However, we achieve a striking data collapse when the
spreading velocity is considered to be a function of the excess energy. Using
the fact that the XXZ chain is integrable, we present an explanation of the
observed velocities in terms of "excitations" in an appropriately defined
generalized Gibbs ensemble.
Archived Files and Locations
|application/pdf 1.6 MB ||