Three-dimensional vortex structure of a fast rotating Bose-Einstein condensate with harmonic-plus-quartic confinement

TL;DR

This paper uses 3D numerical simulations of Bose-Einstein condensates with anharmonic traps to explore vortex structures at high rotation speeds, matching experimental results and revealing complex vortex configurations.

Contribution

It presents the first detailed 3D simulation of fast rotating BECs with realistic parameters, extending understanding of vortex lattice evolution beyond experimental observations.

Findings

Vortex lattice matches experimental size and number for rotation speeds below trap frequency.

Vortex lattice develops a central hole at higher rotation speeds, not seen in experiments.

Good agreement with recent theoretical models on vortex inhomogeneities.

Abstract

We address the challenging proposition of using real experimental parameters in a three-dimensional numerical simulation of fast rotating Bose-Einstein condensates. We simulate recent experiments [V. Bretin, S. Stock, Y. Seurin and J. Dalibard, Phys. Rev. Lett. 92, 050403 (2004); S. Stock, V. Bretin, S. Stock, F. Chevy and J. Dalibard, Europhys. Lett. 65, 594 (2004)] using an anharmonic (quadratic-plus-quartic) confining potential to reach rotation frequencies ($\Omega$) above the trap frequency ($\omega_\perp$). Our numerical results are obtained by propagating the 3D Gross-Pitaevskii equation in imaginary time. For $\Omega \leq\omega_\perp$, we obtain an equilibrium vortex lattice similar (as size and number of vortices) to experimental observations. For $\Omega>\omega_\perp$ we observe the evolution of the vortex lattice into an array of vortices with a central hole. Since this evolution was not visible in experiments, we investigate the 3D structure of vortex configurations and 3D-effects on vortex contrast. Numerical data are also compared to recent theory [D. E. Sheehy and L. Radzihovsky, Phys. Rev. A 70, 063620 (2004)] describing vortex lattice inhomogeneities and a remarkably good agreement is found.