Symmetry-broken momentum distributions induced by matter-wave diffraction during time-of-flight expansion of ultracold atoms

TL;DR

This paper investigates how matter-wave diffraction and interactions during time-of-flight expansion cause symmetry-breaking in momentum distributions of ultracold atoms, affecting measurements and revealing new quantum phenomena.

Contribution

It uncovers the role of matter-wave diffraction and interactions in symmetry-breaking of momentum distributions, with implications for quantum phase studies and interferometry.

Findings

Interaction effects alter initial momentum measurements.

Inter-species scattering causes symmetry breaking.

Diffraction from light fields produces similar effects.

Abstract

We study several effects which lead to symmetry-broken momentum distributions of quantum gases released from optical lattices. In particular, we demonstrate that interaction within the first milliseconds of the time-of-flight expansion can strongly alter the measurement of the initial atomic momentum distribution. For bosonic mixtures in state-dependent lattices, inter-species scattering processes lead to a symmetry breaking in momentum space. The underlying mechanism is identified to be diffraction of the matter wave from the total density lattice, which gives rise to a time-dependent interaction potential. Our findings are of fundamental relevance for the interpretation of time-of-flight measurements and for the study of exotic quantum phases such as the twisted superfluid. Beyond that, the observed matter-wave diffraction can also be used as an interferometric probe. In addition, we report on diffraction from the state-dependent standing light field, which leads to the same symmetry-broken momentum distributions, even for single component condensates.