In-situ Generation of Photon-Memory Entanglement Using an Integrated Rare-Earth Photonic Quantum Memory

Quantum repeaters in quantum networks require either absorptive optical memories or single spin-photon quantum interfaces; however, each of these schemes involve tradeoffs in entanglement rate, efficiency, fidelity and capacity. In this work, we develop a platform that enables in-situ entanglement generation within an absorptive quantum memory; this combines the advantages of both absorptive and emissive memories for photon-memory entanglement that is high-rate, high fidelity, and multi-mode. Our platform is realized by parametrically driving a nonlinear optical cavity which simultaneously couples to an ensemble of ions; experimentally, we demonstrate our platform using an integrated SiC ring resonator on a Er:YSO crystal. We first characterize the SiC resonators, measuring high Q values at telecom wavelengths as well as a pair generation rate of 8,700 pairs/s/mW with an entangled photon bandwidth of 171 MHz. Next, we prepare an atomic frequency comb (AFC) within the inhomogeneously broadened linewidth of Er:YSO and show storage of an entangled photon. With expected AFC storage of 1 μs and finesse of 3, we estimate a memory heralding efficiency greater than 50% and a photon-memory entanglement rate in excess of 1 million Ebits per second. This new in-situ photon-memory entanglement source enables high-rate entanglement distribution over metro-scale telecom quantum networks.