Squeezing of Atomic Quantum Projection Noise

TL;DR

This paper presents a framework for understanding atomic spin squeezing via homodyne measurement, highlighting conditions for metrological relevance and a dual probe scheme that reduces classical noise.

Contribution

It introduces a new theoretical framework for atomic spin squeezing experiments and proposes a dual probe scheme to enhance quantum noise reduction.

Findings

Detection decimates atomic state distribution

Dual probe scheme cancels classical noise sources

Quantum fluctuations dominate the detected signal

Abstract

We provide a framework for understanding recent experiments on squeezing of a collective atomic pseudo-spin, induced by a homodyne measurement on off-resonant probe light interrogating the atoms. The detection of light decimates the atomic state distribution and we discuss the conditions under which the resulting reduced quantum fluctuations are metrologically relevant. In particular, we consider a dual probe scheme which benefits from a cancelation of classical common mode noise sources such that quantum fluctuations from light and atoms are the main contributions to the detected signal.