Variations of the Kibble-Zurek scaling exponents of trapped Bose gases

TL;DR

This study examines how the Kibble-Zurek scaling exponents vary in trapped Bose gases during phase transitions, revealing discrepancies with existing theories and emphasizing the importance of causality effects in inhomogeneous systems.

Contribution

It provides the first comprehensive experimental analysis of vortex formation and Kibble-Zurek scaling in inhomogeneous Bose gases, highlighting deviations from theoretical predictions.

Findings

Observed power-law vortex scaling with quench rate

Enhanced vortex suppression in low-density regions

Significant differences between measured and theoretical KZ exponents

Abstract

We study the vortex nucleation dynamics in inhomogeneous atomic Bose gases quenched into a superfluid phase and investigate the dependence of the Kibble-Zurek (KZ) scaling exponent on the underlying trap configuration. For samples in a number of different inhomogeneous traps, we observe the characteristic power-law scaling of the vortex number with the thermal quench rate, as well as an enhanced vortex suppression in the outer regions with lower particle density, in agreement with the causality effect as encapsulated in the inhomogeneous Kibble-Zurek mechanism (IKZM). However, the measured KZ scaling exponents show significant differences from the theoretical estimates, and furthermore their trends as a function of the underlying trap configuration deviate from the IKZM prediction. We also investigate the early-time coarsening effect using a two-step quench protocol as proposed in a recent study and show that the interpretation of the measurement results without including the causality effect might be misleading. This paper provides a comprehensive study of vortex formation dynamics in quenched Bose gases confined in inhomogeneous trapping potentials and calls for a refined theoretical framework for quantitative understanding of the phase transition and defect formation processes in such inhomogeneous systems.