Prospects and challenges for squeezing-enhanced optical atomic clocks

TL;DR

This paper analyzes how spin squeezed states can improve optical atomic clock stability, showing benefits depend on atom number and laser noise, with current technology favoring smaller ensembles like ion clocks.

Contribution

It provides a quantitative model predicting optimal clock stability with spin squeezing considering laser noise and dead time, highlighting limitations for large ensembles.

Findings

Spin squeezing improves clock stability for small ensembles.

Current lasers limit benefits to ensembles below ~1000 atoms.

Ion clocks can already benefit from spin squeezing with existing lasers.

Abstract

We have investigated the benefits of spin squeezed states for clocks operated with typical Brownian frequency noise-limited laser sources. Based on an analytic model of the closed servo-loop of an optical atomic clock, we can give quantitative predictions on the optimal clock stability for a given dead time and laser noise. Our analytic predictions are in very good agreement with numerical simulations of the closed servo-loop. We find that for usual cyclic Ramsey interrogation of single atomic ensembles with dead time, even with the current most stable lasers spin squeezing can only improve the clock stability for ensembles below a critical atom number of about one thousand in an optical Sr lattice clock. Even with a future improvement of the laser performance by one order of magnitude the critical atom number still remains below 100,000. In contrast, clocks based on smaller, non-scalable ensembles, such as ion clocks, can already benefit from squeezed states with current clock lasers.