Probing the spatial distribution of k-vectors in situ with Bose-Einstein condensates

TL;DR

This paper introduces a new in situ technique using Bose-Einstein condensates to map photon momentum distribution across a laser beam, revealing local recoil effects and aiding in wavefront characterization.

Contribution

The authors develop a novel atom interferometry method to spatially map photon momentum and dispersion in laser beams using BECs as probes.

Findings

Revealed local recoil effects exceeding $h u/c$ in a diffracted beam.

Demonstrated precise in situ wavefront distortion measurement.

Provided insights into systematic biases in quantum sensors.

Abstract

We present a novel method for mapping \textit{in situ} the spatial distribution of photon momentum across a laser beam using a Bose-Einstein condensate (BEC) as a moving probe. By displacing the BEC, we measure the photon recoil by atom interferometry at different positions in the laser beam and thus reconstruct a two-dimensional map of the local intensity and effective dispersion of the $k$ wave vector. Applied to a beam diffracted by a diaphragm, this method reveals a local \textit{extra recoil} effect, which exceeds the magnitude $h\nu/c$ of the individual plane-waves over which the beam can be decomposed. This method offers a new way to precisely characterize wavefront distortions and to evaluate one of the major systematic bias sources in quantum sensors based on atom interferometry.