Speaker
Description
Spin-squeezed states are a prototypical example of metrologically useful states where structured entanglement allows for enhanced sensing with respect to the one possible using classically correlated particles. Relevant aspects are both the efficient preparation of spin-squeezed states and the scalability of estimation precision with the number $N$ of probes. Recently, in the context of the generation of spin-squeezed states via coupling of three-level atoms to an optical cavity and continuous quantum measurement of the transmitted cavity field, it was shown that increasing the atom-cavity coupling can be detrimental to spin-squeezing generation, an effect that is not appreciated in the standard second-order cavity removal approximation [1]. We describe adiabatic elimination techniques to derive an effective Lindblad master equation up to third order in the collective spin operators. We then discuss two approaches to the solution of this equation: a very general one based on a systematic implementation of the truncated cumulant expansion and its numerical solution, which allows to show that the mean field and Gaussian approximations are inadequate to predict the correct spin-squeezing scaling, and a fully analytic one leveraging on the existence of a complete set of commuting weak symmetries [2].
References
[1] A. Caprotti, M. Barbiero, M. G. Tarallo, M. G. Genoni and G. Bertaina, Quantum Sci. Technol., 9, no.3, (2024) 035032
[2] S. G. Giaccari, G. Dellea, M. G. Genoni and G. Bertaina, in preparation