In-situ entanglement generation based on rare-earth quantum memory coupled to a nonlinear cavity (Part I: experimental proposal)

Storage of entangled photons in a quantum memory is critical for optical quantum networks. However, the experimental demonstrations so far face many challenges including source-memory impedance mismatch as well as limited storage times. Here we propose a new scheme that combines a nonlinear optical cavity with an ensemble atomic memory to generate photon-memory entanglement in-situ. In this first talk of the series, we discuss an experiment that consists of an erbium-based solid-state quantum memory coupled to a χ⁽³⁾ nonlinear resonator. We estimate that our design is able to achieve high cooperativity coupling and multimode memory using ¹⁶⁷Er³⁺ hyperfine levels. We also present the spin coherence characterizations of candidate memory materials (¹⁶⁷Er³⁺:YSO and ¹⁶⁷Er³⁺:Y₂O₃) that can enable long-distance entanglement distribution between remote memories.