Phase diagram for a Bose-Einstein condensate moving in an optical lattice

TL;DR

This paper maps the phase diagram of superfluid stability in ultracold bosons within a moving optical lattice, revealing how superfluidity is lost at certain momenta and lattice depths, especially near the Mott insulator transition.

Contribution

It provides a detailed phase diagram for superfluid stability in a moving optical lattice, connecting superfluidity loss to lattice depth and momentum with high precision.

Findings

Superfluid currents become unstable beyond 0.5 recoil momentum in weak lattices.

Superfluidity vanishes at zero momentum near the Mott insulator transition.

Observed a sudden broadening of the transition in a 1D gas in a moving lattice.

Abstract

The stability of superfluid currents in a system of ultracold bosons was studied using a moving optical lattice. Superfluid currents in a very weak lattice become unstable when their momentum exceeds 0.5 recoil momentum. Superfluidity vanishes already for zero momentum as the lattice deep reaches the Mott insulator(MI) phase transition. We study the phase diagram for the disappearance of superfluidity as a function of momentum and lattice depth between these two limits. Our phase boundary extrapolates to the critical lattice depth for the superfluid-to-MI transition with 2% precision. When a one-dimensional gas was loaded into a moving optical lattice a sudden broadening of the transition between stable and unstable phases was observed.