Harnessing superradiance for quantum metrology with spin ensembles

Superradiance is a quintessential collective effect in quantum optics that has seen a recent resurgence of interest; it is also exemplifies the kind of unique physics exhibited by many-body open quantum systems. For entanglement-enhanced quantum metrology, collective decay is often viewed as problematic, as it limits the generation of spin squeezing via Hamiltonian spin-spin interactions. Here, I’ll discuss recent theory work showing how superradiance can in fact be a powerful resource for quantum metrology in setups where spin ensembles are coupled to resonators or cavities. Superradiance can both be used to generate a kind of quantum spin amplification effect, letting systems with highly imperfect readout schemes to benefit from entanglement, and reach sensitive surpassing the standard quantum limit. I will also discuss the “information content” of the output burst of photons generated in superradiant decay, and how this can be used for for a powerful kind of spin readout. These ideas are all motivated by ongoing experiments seeking to both prepare and robustly detect spin squeezing in ensembles of solid state spins (e.g. NV or SiV defects in diamond coupled to microwave resonators).