Orbital many-body dynamics of bosons in the second Bloch band of an optical lattice

TL;DR

This paper investigates the quantum many-body dynamics of a Bose-Einstein condensate in the second Bloch band of an optical lattice, revealing oscillations driven by collisional interactions and modeled by quantum and semi-classical approaches.

Contribution

It demonstrates the orbital many-body oscillations in a BEC within the second Bloch band and compares experimental results with theoretical models, highlighting the role of collisional processes.

Findings

Oscillations driven by on-site and flavor-changing collisions.

Oscillation frequency depends on the ratio of collisional interaction strengths.

Models accurately reproduce the observed dynamics and frequency dependence.

Abstract

A Bose-Einstein condensate (BEC) of rubidium atoms is prepared in one of two degenerate energy minima in the second Bloch band of an optical square lattice. A subsequent oscillation of the BEC between the two energy minima is observed, which is driven by two distinct collision processes: the conventional Hubbard-type on-site collision and a collision process that changes the orbital flavor. The oscillation frequency scales with the relative strength of these collisional interactions, which can be readily tuned via an experimentally well controlled distortion of the unit cell. The observations are compared to a quantum model of two single-particle modes and to a semi-classical multi-band tight-binding simulation of 12x12 tubular sites of the lattice. Both models reproduce the observed oscillatory quantum many-body dynamics and show the correct dependence of the oscillation frequency on the ratio between the strengths of the on-site and flavor-changing collision processes.