Trade-offs between unitary and measurement induced spin squeezing in cavity QED

TL;DR

This paper compares measurement-induced and unitary methods for creating spin squeezing in atomic ensembles within cavity QED, analyzing their effectiveness and limitations under realistic decoherence conditions for quantum metrology.

Contribution

It provides simple criteria to determine when measurement-based entanglement surpasses unitary protocols in spin squeezing, considering all relevant decoherence sources.

Findings

Measurement-based entanglement can outperform unitary protocols under certain conditions.

Decoherence impacts the optimal spin squeezing achievable.

Measurement noise limits the dynamical range of quantum-enhanced phase measurements.

Abstract

We study the combined effects of measurements and unitary evolution on the preparation of spin squeezing in an ensemble of atoms interacting with a single electromagnetic field mode inside a cavity. We derive simple criteria that determine the conditions at which measurement based entanglement generation overperforms unitary protocols. We include all relevant sources of decoherence and study both their effect on the optimal spin squeezing and the overall size of the measurement noise, which limits the dynamical range of quantum-enhanced phase measurements. Our conclusions are relevant for state-of-the-art atomic clocks that aim to operate below the standard quantum limit.