Priyash Barya, Daren Chen, Ashwith Prabhu, Laura Heller, Edmond Chow, Hansol Kim, Joshua Akin, Vasileios Niaouris, Jiefei Zhang, Alan M. Dibos, Pengjie Wang, Elizabeth A. Goldschmidt

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