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

TL;DR

This paper demonstrates that quantum quenches in a 1D spin-1/2 XY model can generate spin-squeezed states and reveals phase-dependent nonanalyticities in long-term spin squeezing behavior, linking quantum criticality to nonequilibrium quantum states.

Contribution

It introduces a protocol for creating spin-squeezed states via quenches and uncovers phase-specific nonanalyticities in long-time spin squeezing, connecting equilibrium phases to nonequilibrium dynamics.

Findings

Quantum quenches can produce spin-squeezed states from initial unsqueezed states.

Nonanalytic behavior in the long-time average of the spin-squeezing parameter occurs at the quantum critical point.

Ferro- and paramagnetic phases exhibit distinct nonequilibrium quantum fluctuation redistribution patterns.

Abstract

We study the time evolution of spin squeezing in the one-dimensional spin-1/2 XY model subject to a sudden quantum quench of a transverse magnetic field. 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. We also identify a nonanalyticity in the long-time average of the spin-squeezing parameter when quenching to the equilibrium quantum critical point. This suggests that the ferro- and paramagnetic phases also define distinct phases for how the transverse field redistributes quantum fluctuations among the spin components away from equilibrium.