Dynamics of quantum vortices at finite temperature

Abstract

In this thesis, we perform investigations into the behaviour of finite-temperature degenerate Bose gases using a classical-field formalism, focussing in particular on the dynamics of quantum vortices in these systems. We demonstrate that the coherence of the classical field can be characterised by its temporal correlations, and discuss how the phase-symmetry-broken averages familiar from mean-field theories emerge from the field trajectories. We show that a finite-temperature condensate containing a precessing vortex in a cylindrically symmetric trap can be realised as an ergodic equilibrium of the classical-field theory, and demonstrate the identification of the rotationally symmetry-broken condensate orbital and core-filling thermal component from the field correlations. We then consider the nonequilibrium dynamics that result when such a precessing-vortex configuration is subjected to a static trap anisotropy which arrests its rotation, and observe novel coupled relaxation dynamics of the condensed and noncondensed components of the field. Finally, we consider the nucleation of vortices in an initially zero-temperature quasi-two-dimensional condensate stirred by a rotating trap anisotropy. We quantify the emergence of a rotating thermal component of the field, which drives the nucleation of vortices from condensate-surface oscillations, and study the relaxation and rotational equilibration of the initially turbulent collection of vortices. We find that thermal fluctuations of the field prevent the vortices from settling into a rigid crystalline lattice in this reduced dimensionality, and that true condensation in the field is completely destroyed by the disordered motion of vortices. We show, however, that the temporal correlations of the field distinguish the quasi-coherent vortex-liquid phase in the trap centre from the truly thermal material in its periphery.

PhD thesis. 276 pages, 49 figures

References in corpus (16)

• Many-Body Physics with Ultracold Gases
• Quantized Rotation of Atoms From Photons with Orbital Angular Momentum
• Spontaneous vortices in the formation of Bose-Einstein condensates
• Emergence of turbulence in an oscillating Bose-Einstein condensate
• Extension of Bogoliubov theory to quasi-condensates
• Observation of Vortex Pinning in Bose-Einstein Condensates
• Quantum corrections to the dynamics of interacting bosons: beyond the truncated Wigner approximation
• Bose-Einstein Condensation from a Rotating Thermal Cloud: Vortex Nucleation and Lattice Formation
• Quantum turbulence and correlations in Bose-Einstein condensate collisions
• Effect of quantum fluctuations on the dipolar motion of Bose-Einstein condensates in optical lattices
• Numerical method for evolving the Projected Gross-Pitaevskii equation
• Instabilities leading to vortex lattice formation in rotating Bose-Einstein condensates
• Dynamical thermalization and vortex formation in stirred 2D Bose-Einstein condensates
• Critical properties of a trapped interacting Bose gas
• Internal One-Particle Density Matrix for Bose-Einstein Condensates with Finite Number of Particles in a Harmonic Potential
• Global singularity-free solution of the Iordanskii force problem