Planar squeezing by quantum non-demolition measurement in cold atomic ensembles

TL;DR

This paper introduces a new method for creating planar squeezed states in cold atomic ensembles using quantum non-demolition measurements, enhancing quantum sensing capabilities in magnetometry.

Contribution

The paper presents a novel scheme for planar squeezing in spin-1 systems via sequential QND measurements, enabling entanglement and improved quantum measurement performance.

Findings

Achieves measurable planar squeezing with various optical depths.

Generated states contain detectable entanglement.

Provides advantages in magnetometry across all precession phases.

Abstract

Planar squeezed states, i.e. quantum states which are squeezed in two orthogonal spin components, have recently attracted attention due to their applications in atomic interferometry and quantum information [Q. Y. He et al, New J. Phys. 14, 093012 (2012)]. While canonical variables such as quadratures of the radiation field can be squeezed in at most one component, simultaneous squeezing in two orthogonal spin components can be achieved due to the angular momentum commutation relations. We present a novel scheme for planar squeezing via quantum non-demolition (QND) measurements in spin-1 systems. The QND measurement is achieved via near-resonant paramagnetic Faraday rotation probing, and the planar squeezing is obtained by sequential QND measurement of two orthogonal spin components. We compute the achievable squeezing for a variety of optical depths, initial conditions, and probing strategies. The planar squeezed states generated in this way contain entanglement detectable by spin-squeezing inequalities and give an advantage relative to non-squeezed states for any precession phase angle, a benefit for single-shot and high-bandwidth magnetometry.