Coupling internal atomic states in a two-component Bose-Einstein condensate via an optical lattice: Extended Mott-superfluid transitions

TL;DR

This paper explores how internal atomic states in a two-component Bose-Einstein condensate coupled via an optical lattice lead to a richer phase diagram with four distinct phases, including novel Mott and superfluid states.

Contribution

It introduces a new phase diagram for coupled two-component BECs, revealing four phases due to internal state coupling, extending the traditional Bose-Hubbard model.

Findings

Identification of four distinct phases: two superfluid and two Mott phases.

Swapping of internal atomic populations at phase transition points.

Full phase diagram derived using strong coupling expansion.

Abstract

An ultracold gas of coupled two-component atoms in an optical field is studied. Due to the internal two-level structure of the atoms, three competing energy terms exist; atomic kinetic, atomic internal, and atom-atom interaction energies. A novel outcome of this interplay, not present in the regular Bose-Hubbard model, is that in the single band and tight binding approximations four different phases appear: two superfluid and two Mott phases. When passing through the critical point between the two superfluid or the two Mott phases, a swapping of the internal atomic populations takes place. By means of the strong coupling expansion, we find the full phase diagram for the four different phases.