Incommensurate superfluidity of bosons in a double-well optical lattice

TL;DR

This paper explores the potential for incommensurate superfluidity in bosons within a double-well optical lattice, highlighting long-lived excited states and symmetry-breaking superfluid phases that could be experimentally observed.

Contribution

It demonstrates that bosons in the first excited band can have long lifetimes and form exotic superfluid states with broken symmetries in a realistic double-well optical lattice.

Findings

Bosons in the excited band can have lifetimes much longer than tunneling times.

The excited band exhibits minima at nonzero, incommensurate momenta.

Potential experimental signatures of the incommensurate superfluid state are discussed.

Abstract

We study bosons in the first excited Bloch band of a double-well optical lattice, recently realized at NIST. By calculating the relevant parameters from a realistic nonseparable lattice potential, we find that in the most favorable cases the boson lifetime in the first excited band can be several orders of magnitude longer than the typical nearest-neighbor tunnelling timescales, in contrast to that of a simple single-well lattice. In addition, for sufficiently small lattice depths the excited band has minima at nonzero momenta incommensurate with the lattice period, which opens a possibility to realize an exotic superfluid state that spontaneously breaks the time-reversal, rotational, and translational symmetries. We discuss possible experimental signatures of this novel state.