Achieving spin-squeezed states by quench dynamics in a quantum chain

Abstract

We study the time evolution of spin squeezing in the one-dimensional spin-1/2 XY model with a transverse magnetic field subject to a sudden quantum quench. The initial state is selected from the ground state phase diagram of the model, consisting of ferro-and paramagnetic phases separated by a critical value of the transverse field. Our analysis, based on exact results for the model, reveals that by a proper choice of protocol, a quantum quench from an unsqueezed state can create spin squeezed nonequilibrium states. Moreover, we identify two types of nonanalyticities in the parameter which measures the amount of spin squeezing in the system: one in its time-dependence, the other in its long-time average with the transverse field as control parameter. We argue that the first type of nonanalyticity signals an unconventional nonequilibrium quantum phase transition, appearing at certain critical times when the direction of spin squeezing suddenly changes.