Spontaneous Four-Wave Mixing of de Broglie Waves: Beyond Optics

TL;DR

This paper explores the atom-optical analog of four-wave mixing using Bose-Einstein condensates, revealing complex momentum distributions influenced by many-body effects and interactions, beyond the optical analogy.

Contribution

It demonstrates the deviation from simple phase matching in atom-optical four-wave mixing, showing an ellipsoidal momentum distribution due to many-body effects.

Findings

Scattered atoms' momenta form an ellipsoid smaller than the initial collision momentum

Numerical and analytical models agree with experimental measurements

Many-body effects and mean-field interactions influence the scattering process

Abstract

We investigate the atom-optical analog of degenerate four-wave mixing of photons by colliding two Bose-Einstein condensates (BECs) of metastable helium and measuring the resulting momentum distribution of the scattered atoms with a time and space resolved detector. For the case of photons, phase matching conditions completely define the final state of the system, and in the case of two colliding BECs, simple analogy implies a spherical momentum distribution of scattered atoms. We find, however, that the final momenta of the scattered atoms instead lie on an ellipsoid whose radii are smaller than the initial collision momentum. Numerical and analytical calculations agree well with the measurements, and reveal the interplay between many-body effects, mean-field interaction, and the anisotropy of the source condensate.