Quantum quenches in a spinor condensate

TL;DR

This paper investigates the non-equilibrium dynamics of a spin-1 condensate during quantum quenches, revealing how different quench protocols lead to distinct ordering phenomena, vortex creation, and coarsening behaviors, with relevance to recent experiments.

Contribution

It provides a detailed analysis of the ordering dynamics, vortex formation, and coarsening in spinor condensates during quenches, highlighting the dependence on quench rate and endpoint, and connecting theory with experiments.

Findings

Quenching induces XY order at specific wavevectors or light-cone correlations.

Kibble-Zurek mechanism governs the ordering scale during finite-rate quenches.

Vortex creation and coarsening dynamics depend on the quench endpoint and field conditions.

Abstract

We discuss the ordering of a spin-1 condensate when quenched from its paramagnetic phase to its ferromagnetic phase by reducing magnetic field. We first elucidate the nature of the equilibrium quantum phase transition. Quenching rapidly through this transition reveals XY ordering either at a specific wavevector, or the `light-cone' correlations familiar from relativistic theories, depending on the endpoint of the quench. For a quench proceeding at a finite rate the ordering scale is governed by the Kibble-Zurek mechanism. The creation of vortices through growth of the magnetization fluctuations is also discussed. The long time dynamics again depends on the endpoint, conserving the order parameter in zero field, but not at finite field, with differing exponents for the coarsening of magnetic order. The results are discussed in the light of a recent experiment by Sadler \emph{et al.}