Interaction-induced excited-band condensate in a double-well optical lattice

TL;DR

This paper theoretically demonstrates that interactions in a double-well optical lattice can induce Bose-Einstein condensates in excited energy bands, revealing new possibilities for manipulating quantum states in optical lattices.

Contribution

It introduces a novel mechanism where interactions induce excited-band condensates in double-well optical lattices, including symmetric and asymmetric configurations.

Findings

Condensates form in excited bands at the Brillouin Zone edge for symmetric lattices.

Asymmetric lattices induce zero-momentum condensates in excited bands.

The mechanism involves interaction effects reducing band gaps and breaking inversion symmetry.

Abstract

We show theoretically that interaction effects in a double-well optical lattice can induce condensates in an excited band. For a symmetric double-well lattice, bosons condense into the bottom of the excited band at the edge of the Brillouin Zone if the chemical potential is above a critical value. For an asymmetric lattice, a condensate with zero momentum is automatically induced in the excited band by the condensate in the lowest band. This is due to a combined effect of interaction and lattice potential, which reduces the band gap and breaks the inversion symmetry. Our work can be generalized to a superlattice composed of multiple-well potentials at each lattice site, where condensates can be induced in even higher bands.