Effect of the lattice alignment on Bloch oscillations of a Bose-Einstein condensate in a square optical lattice

TL;DR

This paper investigates how the alignment of an external force affects the stability and behavior of Bloch oscillations in a Bose-Einstein condensate within a square optical lattice, revealing alignment-dependent stability conditions.

Contribution

It provides a comparative analysis of stability conditions for Bloch oscillations under different force alignments, combining mean field and microscopic approaches.

Findings

Aligned forces lead to stable Bloch oscillations predictable by mean field theory.

Misaligned forces cause periodic modulation of oscillations, requiring microscopic analysis.

Stability depends critically on the force's orientation relative to lattice axes.

Abstract

We consider a Bose-Einstein condensate of ultracold atoms loaded into a square optical lattice and subject to a static force. For vanishing atom-atom interactions the atoms perform periodic Bloch oscillations for arbitrary direction of the force. We study the stability of these oscillations for non-vanishing interactions, which is shown to depend on an alignment of the force vector with respect to the lattice crystallographic axes. If the force is aligned along any of the axes, the mean field approach can be used to identify the stability conditions. On the contrary, for a misaligned force one has to employ the microscopic approach, which predicts periodic modulation of Bloch oscillations in the limit of a large forcing.