Single-shot readout of ¹⁷¹Yb:YVO ions embedded in a nanophotonic cavity

Solid-state emitters coupled to photonic resonators are an attractive platform for building quantum light-matter interfaces required for scalable quantum networks. Rare-earth ions (REIs) in solids offer a promising system for such interfaces due to their long optical and spin coherence times at cryogenic temperatures, but harnessing these properties at the single ion level has proven to be challenging due to the inherently weak coupling of REIs with light. Here we present the initialization, coherent manipulation, and readout of individual ytterbium-171 ions embedded in a nanophotonic cavity fabricated directly in the yttrium orthovanadate (YVO) host crystal. These ions possess coupled electron-nuclear spin states that are first-order insensitive to magnetic field fluctuations, which allows for optical linewidths less than 1 MHz and spin coherence times greater than 30 ms. We show that Purcell enhancement in the nanophotonic cavity increases the optical emission rate by a factor of 120 and improves the cyclicity of the cavity-coupled optical transitions, which enables efficient initialization and conditional single-shot readout of the hyperfine spin state with fidelity greater than 95%.