# Vortex proliferation in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional lattice of Bose-Einstein condensates

## TL;DR

This study observes vortex proliferation in a 2D lattice of Bose-Einstein condensates within the BKT regime, demonstrating thermal activation as the vortex formation mechanism and analyzing vortex pair sizes as coupling varies.

## Contribution

It provides experimental evidence of vortex proliferation and thermal activation in a 2D BEC lattice, advancing understanding of BKT physics in quantum gases.

## Key findings

- Vortices appear as Josephson energy decreases relative to thermal energy.
- Vortex formation is confirmed to be thermally activated.
- Data on vortex pair sizes as a function of coupling strength are obtained.

## Abstract

We observe the proliferation of vortices in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional array of Josephson-coupled Bose-Einstein condensates. As long as the Josephson (tunneling) energy J exceeds the thermal energy T, the array is vortex-free. With decreasing J/T, vortices appear in the system in ever greater numbers. We confirm thermal activation as the vortex formation mechanism and obtain information on the size of bound vortex pairs as J/T is varied.