Ordered structures in rotating ultracold Bose gases

TL;DR

This paper investigates how small samples of rotating ultracold bosonic atoms form ordered structures and vortices, revealing unique behaviors for fewer than 10 atoms that differ from large system predictions.

Contribution

It provides a detailed analysis of ground state structures and vortex behavior in small rotating Bose gases, highlighting deviations from standard large-system scenarios.

Findings

Ordered structures emerge as rotation increases.

Vortex contribution to angular momentum shows peaks and minima for small N.

Standard vortex behavior is absent for N<10, only gradually appearing as N increases.

Abstract

The characterization of small samples of cold bosonic atoms in rotating microtraps has recently attracted increasing interest due to the possibility to deal with a few number of particles per site in optical lattices. We analyze the evolution of ground state structures as the rotational frequency $\Omega$ increases. Various kinds of ordered structures are observed. For $N<10$ atoms, the standard scenario, valid for large sytems, is absent, and only gradually recovered as $N$ increases. The vortex contribution to the total angular momentum $L$ as a function of $\Omega$ ceases to be an increasing function of $\Omega$, as observed in experiments of Chevy {\it et al.} (Phys. Rev. Lett. 85, 2223 (2000)). Instead, for small $N$, it exhibits a sequence of peaks showing wide minima at the values of $\Omega$, where no vortices appear.