Nondestructive optomechanical detection scheme for Bose-Einstein condensates

TL;DR

This paper introduces a nondestructive two-tone heterodyne optical readout method for Bose-Einstein condensates that measures density correlations and surpasses the standard quantum limit using squeezed states, with applications to quantum vacuum fluctuation effects.

Contribution

It proposes a novel optical detection scheme for BECs that can measure unequal-time correlations and go beyond quantum noise limits using squeezed states.

Findings

Identified the standard quantum limit for the measurement scheme.

Demonstrated how squeezed states can surpass this limit.

Showcased potential to observe quantum vacuum effects like the Unruh effect.

Abstract

We present a two-tone heterodyne optical readout scheme to extract unequal-time density correlations along an arbitrary stationary interaction path from a pancake-shaped Bose-Einstein condensate, using a modulated laser probe. Analysing the measurement noise both from imprecision and backaction, we identify the standard quantum limit for the signal-extraction scheme, and examine how a class of two-mode squeezed initial states can be used to push beyond this limit. As an application, we show how the readout scheme can be used for an experimentally feasible realisation of acceleration-dependence of quantum-vacuum fluctuations in the system, including the analogue spacetime circular motion Unruh effect. The scheme is adaptable beyond Bose-Einstein condensates, providing nondestructive access to unequal-time correlations in quantum fluids.