Squeezed superradiance enables robust entanglement-enhanced metrology even with highly imperfect readout

Abstract

Quantum metrology protocols using entangled states of large spin ensembles attempt to achieve measurement sensitivities surpassing the standard quantum limit (SQL), but in many cases they are severely limited by even small amounts of technical noise associated with imperfect sensor readout. Amplification strategies based on time-reversed coherent spin-squeezing dynamics have been devised to mitigate this issue, but are unfortunately very sensitive to dissipation, requiring a large single-spin cooperativity to be effective. Here, we propose a new dissipative protocol that combines amplification and squeezed fluctuations. It enables the use of entangled spin states for sensing well beyond the SQL even in the presence of significant readout noise. Further, it has a strong resilience against undesired single-spin dissipation, requiring only a large collective cooperativity to be effective.

6+9 pages, 3+3 figures; equivalent to published version; a reference to a previously unpublished manuscript has been updated

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• Critical steady states of all-to-all squeezed and driven superradiance: An analytic approach
• Robust incoherent perfect absorption
• Non-Gaussian generalized two-mode squeezing: applications to two-ensemble spin squeezing and beyond
• Entangling cavity-magnon polaritons by interacting with phonons
• Reconfigurable dissipative entanglement between many spin ensembles: from robust quantum sensing to many-body state engineering