Low velocity quantum reflection of Bose-Einstein condensates

TL;DR

This study investigates quantum reflection of Bose-Einstein condensates on silicon pillars, revealing velocity-dependent reflection probabilities and collective excitations at low velocities, supported by a theoretical model.

Contribution

It provides the first experimental evidence of velocity-dependent quantum reflection saturation and introduces a model explaining reduced reflectivity due to combined potentials.

Findings

Reflection probability increases with decreasing velocity but saturates around 60%

Observed collective excitations in reflected condensates at low velocities

Theoretical model matches experimental data on reflectivity saturation

Abstract

We studied quantum reflection of Bose-Einstein condensates at normal incidence on a square array of silicon pillars. For incident velocities of 2.5-26 mm/s observations agreed with theoretical predictions that the Casimir-Polder potential of a reduced density surface would reflect slow atoms with much higher probability. At low velocities (0.5-2.5 mm/s), we observed that the reflection probability saturated around 60% rather than increasing towards unity. We present a simple model which explains this reduced reflectivity as resulting from the combined effects of the Casimir-Polder plus mean field potential and predicts the observed saturation. Furthermore, at low incident velocities, the reflected condensates show collective excitations.