Superfluid drag of two-species Bose-Einstein condensates in optical lattices

TL;DR

This paper investigates how the superfluid drag between two-species Bose-Einstein condensates in optical lattices depends on lattice geometry, depth, and atomic mass ratios, revealing a non-monotonic relationship influenced by interactions and kinetic energy.

Contribution

It provides a numerically exact analysis of superfluid drag in two-species BECs in optical lattices, highlighting the non-monotonic dependence on lattice depth and relevance to experimental conditions.

Findings

Drag increases with kinetic energy.

Superfluid-drag coefficient varies non-monotonically with lattice depth.

Results are relevant for atomic species with different mass ratios.

Abstract

We study two-species Bose-Einstein condensates in quasi two-dimensional optical lattices of varying geometry and potential depth. Based on the numerically exact Bloch and Wannier functions obtained using the plane-wave expansion method, we quantify the drag (entrainment coupling) between the condensate components. This drag originates from the (short range) inter-species interaction and increases with the kinetic energy. As a result of the interplay between interaction and kinetic energy effects, the superfluid-drag coefficient shows a non-monotonic dependence on the lattice depth. To make contact with future experiments, we quantitatively investigate the drag for mass ratios corresponding to relevant atomic species.