Beating standard quantum limit via two-axis magnetic susceptibility measurement

TL;DR

This paper introduces a quantum metrology scheme that measures magnetic susceptibility along two axes to estimate a parameter with precision surpassing the standard quantum limit, using spin squeezing and optimized measurement strategies.

Contribution

It presents a practical two-axis magnetic susceptibility measurement method that beats the standard quantum limit using atomic spin squeezing and optimized parameter estimation.

Findings

Achieved parameter estimation precision scaling better than the standard quantum limit.

Demonstrated a measurement scheme that is easy to implement for practical quantum metrology.

Provided a detailed analysis of the precision scaling with the number of atomic spins.

Abstract

We report a metrology scheme which measures magnetic susceptibility of an atomic spin ensemble along the $x$ and $z$ direction and produces parameter estimation with precision beating the standard quantum limit. The atomic ensemble is initialized via one-axis spin squeezing with optimized squeezing time and parameter $\phi$ to be estimated is assumed as uniformly distributed between 0 and $2\pi$. One estimation of $\phi$ can be produced with every two magnetic susceptibility data measured along the two axis respectively, which has imprecision scaling $(1.43\pm{}0.02)/N^{0.687\pm0.003}$ with respect to the number N of atomic spins. The measurement scheme is easy to implement and thus one step towards practical application of quantum metrology.