Proposal for spin squeezing in rare-earth-ion-doped crystals with a four-color scheme

Abstract

Achieving spin squeezing within solid-state devices is a long-standing research goal due to the promise of their particularities, for instance, their long coherence times, the possibility of low-temperature experiments, or the integration of entanglement-assisted sensors on-chip. In this work, we investigate an interferometer-free four-color scheme to achieve spin squeezing of rare-earth-ion-doped crystals. The proposal relies on an analytic derivation that starts from a Tavis-Cummings model for light-matter interaction, providing microscopic insights onto spin-squeezing generation. We evince the spin-squeezing signature in the light intensity variance. We consider the two particular cases of europium- and praseodymium-doped yttrium orthosilicates, workhorses of quantum technology developments. We show that up to 8 dB of spin squeezing can be obtained with readily accessible experimental resources, including noise due to photon scattering. Our results for rare-earth-ion-doped crystals add to the promising properties of these platforms for manipulating many-body entangled states and for high-precision measurements.