Effective thermal dynamics following a quantum quench in a spin chain

We study the nonequilibrium dynamics of the quantum Ising model following an abrupt quench of the transverse field. We focus on the on-site autocorrelation function of the order parameter, and extract the phase-coherence time τQφ from its asymptotic behavior. We show that the initial state determines τQφ only through an effective temperature set by its energy and the final Hamiltonian. Moreover, we observe that the dependence of τQφ on the effective temperature fairly agrees with that obtained in thermal equilibrium as a function of the equilibrium temperature. © 2009 The American Physical Society.