Telecom Quantum Memory over 1 μs in Nanophotonic Lithium Niobate.

Nanophotonic quantum memory is a vital component for scalable quantum information processing for quantum computing, networking, and sensing applications. We store single-photon-level telecom-band optical pulses for more than 1 μs using an atomic frequency comb in erbium-doped thin-film lithium niobate (TFLN), well beyond what is practically feasible via propagation in even the best nanophotonic devices due to propagation losses. We verify the quantum nature of this storage by demonstrating the phase coherence and subsingle-photon noise upon retrieval. We also show the flexibility of our platform by storing up to 20 temporal modes and demonstrating an acceptance bandwidth of up to 2.2 GHz. These results establish erbium-doped TFLN as a practical platform for on-chip quantum memory at telecom wavelengths, a key missing element for photonic quantum computing and quantum networking.