Interaction broadening of Wannier functions and Mott transitions in atomic BEC

TL;DR

This paper studies how interactions in atomic BECs in optical lattices affect Wannier functions and the superfluid to Mott-insulator transition, highlighting the importance of interaction-induced broadening for accurate modeling.

Contribution

It introduces a method to construct interaction-broadened Wannier functions accounting for mean field repulsion, improving the accuracy of transition predictions.

Findings

Interaction broadening significantly affects the critical lattice depth in 3D lattices.

The approach shows notable differences from single-atom Wannier functions.

The validity of the single band model is critically discussed.

Abstract

Superfluid to Mott-insulator transitions in atomic BEC in optical lattices are investigated for the case of number of atoms per site larger than one. To account for mean field repulsion between the atoms in each well, we construct an orthogonal set of Wannier functions. The resulting hopping amplitude and on-site interaction may be substantially different from those calculated with single-atom Wannier functions. As illustrations of the approach we consider lattices of various dimensionality and different mean occupations. We find that in three-dimensional optical lattices the correction to the critical lattice depth is significant to be measured experimentally even for small number of atoms. Finally, we discuss validity of the single band model.