Entanglement-assisted atomic clock beyond the projection noise limit

TL;DR

This paper demonstrates an entanglement-enhanced atomic clock using spin squeezing via quantum non-demolition measurement, surpassing the projection noise limit and improving signal-to-noise ratio in a proof-of-principle experiment with cold cesium atoms.

Contribution

It is the first to operate an atomic clock beyond the projection noise limit using entanglement and spin squeezing techniques.

Findings

Achieved 1.1 dB improvement in signal-to-noise ratio.

Used quantum non-demolition measurement to generate spin squeezed states.

Operated with a clock-interrogation time of 10 microseconds.

Abstract

We use a quantum non-demolition measurement to generate a spin squeezed state and to create entanglement in a cloud of 10^5 cold cesium atoms, and for the first time operate an atomic clock improved by spin squeezing beyond the projection noise limit in a proof-of-principle experiment. For a clock-interrogation time of 10 \mu\s the experiments show an improvement of 1.1 dB in the signal-to-noise ratio, compared to the atomic projection noise limit.