Finite-momentum Bose-Einstein condensates in shaken 2D square optical lattices

TL;DR

This paper demonstrates how shaking a 2D optical lattice can induce finite-momentum Bose-Einstein condensates by tuning hopping parameters, revealing new phases and experimental signatures in ultracold bosonic systems.

Contribution

It introduces a method to generate finite-momentum condensates in shaken optical lattices by controlling hopping renormalization and anisotropy, expanding the possibilities for quantum phase engineering.

Findings

Finite-momentum condensates can be realized by shaking the lattice.

Phase boundaries between Mott insulator and superfluid phases are mapped.

Time-of-flight images can reveal the finite-momentum condensate states.

Abstract

We consider ultracold bosons in a 2D square optical lattice described by the Bose-Hubbard model. In addition, an external time-dependent sinusoidal force is applied to the system, which shakes the lattice along one of the diagonals. The effect of the shaking is to renormalize the nearest-neighbor hopping coefficients, which can be arbitrarily reduced, can vanish, or can even change sign, depending on the shaking parameter. It is therefore necessary to account for higher-order hopping terms, which are renormalized differently by the shaking, and introduce anisotropy into the problem. We show that the competition between these different hopping terms leads to finite-momentum condensates, with a momentum that may be tuned via the strength of the shaking. We calculate the boundaries between the Mott-insulator and the different superfluid phases, and present the time-of-flight images expected to be observed experimentally. Our results open up new possibilities for the realization of bosonic analogs of the FFLO phase describing inhomogeneous superconductivity.