Rapidly Rotating Bose-Einstein Condensates in and near the Lowest Landau Level

TL;DR

This paper reports the creation of rapidly rotating Bose-Einstein condensates in the lowest Landau level, revealing a vortex lattice with reduced shear strength and a transition towards ideal-gas behavior as the system becomes quasi-two-dimensional.

Contribution

It demonstrates achieving the quantum Hall regime in Bose-Einstein condensates by high rotation rates and reduced atom numbers, and observes associated changes in vortex lattice and collective modes.

Findings

Ordered vortex lattice persists at high rotation

Shear strength of vortex lattice is significantly reduced

Axial breathing mode frequency shifts towards ideal-gas behavior

Abstract

We create rapidly rotating Bose-Einstein condensates in the lowest Landau level, by spinning up the condensates to rotation rates $\Omega>99%$ of the centrifugal limit for a harmonically trapped gas, while reducing the number of atoms. As a consequence, the chemical potential drops below the cyclotron energy $2\hbar\Omega$. While in this mean-field quantum Hall regime we still observe an ordered vortex lattice, its elastic shear strength is strongly reduced, as evidenced by the observed very low frequency of Tkachenko modes. Furthermore, the gas approaches the quasi-two-dimensional limit. The associated cross-over from interacting- to ideal-gas behavior along the rotation axis results in a shift of the axial breathing mode frequency.