Back-action evading measurement of the collective mode of a Bose-Einstein condensate

TL;DR

This paper proposes a theoretical method for back-action evading measurement of a Bose-Einstein condensate's collective mode using an optical cavity with modulated laser drive, achieving noise suppression below the SQL.

Contribution

It introduces a novel amplitude modulation scheme enabling quantum nondemolition measurement of BEC collective modes with reduced backaction and tunable precision.

Findings

Back-action noise is negligible in the good-cavity limit.

Measurement noise is below the standard quantum limit even in the bad-cavity limit.

Measurement precision can be controlled via atomic collision interactions.

Abstract

In this paper, we investigate theoretically the back-action evading measurement of the collective mode of an interacting atomic Bose-Einstein condensate (BEC) trapped in an optical cavity which is driven coherently by a pump laser with a modulated amplitude. It is shown that for a specified kind of amplitude modulation of the driving laser, one can measure a generalized quadrature of the collective mode of the BEC indirectly through the output cavity field with a negligible backaction noise in the good-cavity limit. Nevertheless, the on-resonance added noise of measurement is suppressed below the standard quantum limit (SQL) even in the bad cavity limit. Moreover, the measurement precision can be controlled through the s-wave scattering frequency of atomic collisions.