Expansion of a quantum gas released from an optical lattice

TL;DR

This paper investigates how finite time-of-flight effects alter the interference patterns of ultracold atoms released from optical lattices, revealing deviations from simple momentum distribution interpretations.

Contribution

It demonstrates that finite time-of-flight can significantly modify interference patterns, introducing near-field diffraction effects in quantum gas experiments.

Findings

Finite time-of-flight alters interference patterns.

Near-field diffraction effects are significant.

Simulations match experimental observations.

Abstract

We analyze the interference pattern produced by ultracold atoms released from an optical lattice. Such interference patterns are commonly interpreted as the momentum distributions of the trapped quantum gas. We show that for finite time-of-flights the resulting density distribution can, however, be significantly altered, similar to a near-field diffraction regime in optics. We illustrate our findings with a simple model and realistic quantum Monte Carlo simulations for bosonic atoms, and compare the latter to experiments.