Wafer-scale rare-earth qubits with milliseconds coherence time

..Rare-Earth(RE) qubits in solids are a promising platform for quantum repeaters and hybrid quantum systems due to the long spin coherence time and narrow optical linewidths of rare-earth ions. We demonstrate epitaxially grown RE-doped thin films^[1]with long coherence times, enabling large-scale device fabrication for quantum information processing. We address erbium (Er3+) dopants in epitaxial Y2O3 thin film on a wafer-scale with high sensitivity pulsed electron spin resonance (ESR) using superconducting microwave resonators and demonstrate long spin coherence time on par with bulk crystals. We perform Purcell-enhanced readout of single Er3+ions optically using cryogenic fiber Fabry-Perot cavity and discuss the directions towards obtaining transform-limited single optical emitters. Our results demonstrate long coherence times in rare-earth doped thin films which will allow for large-scale development of RE-based quantum interconnects, and sensors as well as enable the study of novel physics of RE spin-phonon, spin-spin interactions.