Improved absolute clock stability by the joint interrogation of two atomic states

TL;DR

This paper introduces a joint interrogation method for atomic clocks that extends phase measurement range, reduces phase slips, and enhances stability, supported by simulations and adaptable to current experiments.

Contribution

It proposes a novel joint interrogation strategy for atomic clocks that improves stability by extending phase measurement range and incorporating spin-squeezing techniques.

Findings

Extended phase measurement range from [-π/2, π/2] to [-π, π]

Simulation shows improved stability with correlated LO noise

Spin-squeezing further enhances clock stability scaling

Abstract

Improving the clock stability is of fundamental importance for the development of quantum-enhanced metrology. One of the main limitations arises from the randomly-fluctuating local oscillator (LO) frequency, which introduces "phase slips" for long interrogation times and hence failure of the frequency-feedback loop. Here we propose a strategy to improve the stability of atomic clocks by interrogating two out-of-phase state sharing the same LO. While standard Ramsey interrogation can only determine phases unambiguously in the interval $[-\pi/2,\pi/2]$, the joint interrogation allows for an extension to $[-\pi,\pi]$, resulting in a relaxed restriction of the Ramsey time and improvement of absolute clock stability. Theoretical predictions are supported by ab-initio numerical simulation for white and correlated LO noise. While our basic protocol uses uncorrelated atoms, we have further extended it to include spin-squeezing and further improving the scaling of clock stability with the number of atoms. Our protocol can be readily tested in current state-of-the-art experiments.