Loss of superfluidity in the Bose-Einstein condensate in an optical lattice with cubic and quintic nonlinearity

TL;DR

This paper investigates how cubic and quintic nonlinearities in a Bose-Einstein condensate within an optical lattice affect superfluidity, revealing its loss through a dynamical phase transition and identifying new phases.

Contribution

It predicts the loss of superfluidity due to modulational instability and uncovers a stripe phase and a density wave insulating phase in the system.

Findings

Superfluid density wave exists only with both nonlinearities present.

Loss of superfluidity occurs via a classical dynamical phase transition.

Discovery of a density wave insulating phase with frequency modulations.

Abstract

In a one-dimensional shallow optical lattice, in the presence of both cubic and quintic nonlinearity, a superfluid density wave is identified in a Bose-Einstein condensate. Interestingly, it ceases to exist when only one of these interactions is operative. We predict the loss of superfluidity through a classical dynamical phase transition, where modulational instability leads to the loss of phase coherence. In a certain parameter domain, the competition between lattice potential and the interactions is shown to give rise to a stripe phase, where atoms are confined in finite domains. In a pure two-body case, apart from the known superfluid and insulating phases, a density wave insulating phase is found to exist, possessing two frequency modulations commensurate with the lattice potential.