Dynamical thermalization and vortex formation in stirred 2D Bose-Einstein condensates

TL;DR

This paper models the stirring of 2D Bose-Einstein condensates using classical field techniques, revealing vortex formation into a disordered vortex liquid driven by turbulence and thermalization.

Contribution

It introduces a Hamiltonian classical field approach that conserves atom number and energy, and demonstrates vortex nucleation and thermalization in stirred 2D condensates.

Findings

Vortex nucleation occurs without lattice formation, resulting in a vortex liquid.

Vacuum fluctuations seed dynamical instability and turbulence.

Thermal components emerge, enabling vortex damping and dissipation.

Abstract

We present a quantum mechanical treatment of the mechanical stirring of Bose-Einstein condensates using classical field techniques. In our approach the condensate and excited modes are described using a Hamiltonian classical field method in which the atom number and (rotating frame) energy are strictly conserved. We simulate a T = 0 quasi-2D condensate perturbed by a rotating anisotropic trapping potential. Vacuum fluctuations in the initial state provide an irreducible mechanism for breaking the initial symmetries of the condensate and seeding the subsequent dynamical instability. Highly turbulent motion develops and we quantify the emergence of a rotating thermal component that provides the dissipation necessary for the nucleation and motional-damping of vortices in the condensate. Vortex lattice formation is not observed, rather the vortices assemble into a spatially disordered vortex liquid state. We discuss methods we have developed to identify the condensate in the presence of an irregular distribution of vortices, determine the thermodynamic parameters of the thermal component, and extract damping rates from the classical field trajectories.