Feedback control of an interacting Bose-Einstein condensate using phase-contrast imaging

TL;DR

This paper demonstrates a feedback control scheme using phase-contrast imaging to stabilize the spatial mode of an interacting Bose-Einstein condensate, addressing linewidth limitations in atom lasers.

Contribution

It extends existing feedback theory to strongly interacting BECs by incorporating measurement backaction and fixed number state approximation, improving control effectiveness.

Findings

Control is more effective with larger nonlinearity.

The model accounts for measurement backaction in a realistic setup.

It overcomes mean-field approximation limitations for strongly interacting BECs.

Abstract

The linewidth of an atom laser is limited by density fluctuations in the Bose-Einstein condensate (BEC) from which the atom laser beam is outcoupled. In this paper we show that a stable spatial mode for an interacting BEC can be generated using a realistic control scheme that includes the effects of the measurement backaction. This model extends the feedback theory, based on a phase-contrast imaging setup, presented in \cite{Szigeti:2009}. In particular, it is applicable to a BEC with large interatomic interactions and solves the problem of inadequacy of the mean-field (coherent state) approximation by utilising a fixed number state approximation. Our numerical analysis shows the control to be more effective for a condensate with a large nonlinearity.