Nonlinear looped band structure of Bose-Einstein condensates in an optical lattice

TL;DR

This paper experimentally investigates the stability of nonlinear, looped band structures in Bose-Einstein condensates within an optical lattice, revealing decay behaviors and the significance of correlations beyond mean-field theory.

Contribution

It demonstrates the experimental realization and stability analysis of nonlinear looped band structures in BECs, highlighting the role of correlations beyond mean-field models.

Findings

Distinct decay rates confirm multivalued, looped band structure.

Double well lattice stabilizes and enables dynamic preparation of loop states.

Loop states are more stable than unstable ground states but decay faster than mean-field predictions.

Abstract

We study experimentally the stability of excited, interacting states of bosons in a double-well optical lattice in regimes where the nonlinear interactions are expected to induce "swallowtail" looped band structure. By carefully preparing different initial coherent states and observing their subsequent decay, we observe distinct decay rates that provide direct evidence for multivalued, looped band structure. The double well lattice both stabilizes the looped band structure and allows for dynamic preparation of different initial states, including states within the loop structure. We confirm our state preparation procedure with dynamic Gross-Pitaevskii calculations. The excited loop states are found to be more stable than dynamically unstable ground states, but decay faster than expected based on a mean-field stability calculation, indicating the importance of correlations beyond a mean field description.