Impact of Non-Unitary Spin Squeezing on Atomic Clock Performance

TL;DR

This paper investigates how non-unitary spin squeezing, affected by experimental imperfections, reduces potential improvements in atomic clock stability, emphasizing the need for nearly pure entangled states.

Contribution

It provides analytic formulas linking non-unitary spin squeezing effects to atomic clock performance, highlighting the importance of high-quality entangled states.

Findings

Non-unitary spin squeezing significantly reduces clock stability gains.

Analytic formulas relate squeezing, noise, and contrast to performance.

Nearly pure entangled states are crucial for optimal clock improvements.

Abstract

Spin squeezing is a form of entanglement that can improve the stability of quantum sensors operating with multiple particles, by inducing inter-particle correlations that redistribute the quantum projection noise. Previous analyses of potential metrological gain when using spin squeezing were performed on theoretically ideal states, without incorporating experimental imperfections or inherent limitations which result in non-unitary quantum state evolution. Here, we show that potential gains in clock stability are substantially reduced when the spin squeezing is non-unitary, and derive analytic formulas for the clock performance as a function of squeezing, excess spin noise, and interferometer contrast. Our results highlight the importance of creating and employing nearly pure entangled states for improving atomic clocks.