Investigation of the momentum distribution of an excited BEC by free expansion: coupling with collective modes

TL;DR

This study examines how a Bose-Einstein condensate's momentum distribution evolves after external excitation, revealing its coupling with collective quadrupolar modes during free expansion, which complicates direct measurement.

Contribution

It demonstrates the link between momentum distribution changes and quadrupolar collective modes in a BEC after excitation, highlighting the influence of collective oscillations on observed momentum profiles.

Findings

Momentum distribution is affected by quadrupolar oscillations.

Center-of-mass dipolar mode has negligible impact.

Coupling with collective modes complicates direct momentum measurement.

Abstract

We investigate the evolution of the momentum distribution of a Bose-Einstein condensate subjected to an external small oscillatory perturbation as a function of the in-trap evolution of the condensate after the external perturbation is switched-off. Besides changing its momentum distribution, we observe that the cloud distributes the input energy among its normal collective modes, displaying center-of-mass dipolar mode and quadrupolar mode. While the dipolar mode can be easily disregarded, we show that the momentum distribution is closely tied to the quadrupolar oscillation mode. This convolution hinders the actual momentum distribution.