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arXiv:2605.14777

Programmable cavity-enhanced telecom quantum memory in thin-film lithium niobate

Chengdong Yang, Hanwen Guo, Yu-Yang An, Qian He, Chi Lu, Ziheng Jiang, Yan-Qing Lu, Shining Zhu, Xiao-Song Ma

quant-phphysics.opticsSubmitted May 14, 2026• Announced May 15, 2026• 1 citation
v1 · May 14, 2026v2 · Jul 15, 2026
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Abstract

Spectrally multiplexed telecom quantum networks require quantum memories that combine efficient storage with programmable frequency addressing. An ideal integrated implementation should therefore unite a native telecom transition, efficient storage and fast on-chip spectral control. Here we demonstrate a cavity-enhanced quantum memory in an isotopically purified $^{167}\mathrm{Er}^{3+}$-doped thin-film lithium niobate microring resonator. Long-lived hyperfine shelving states support persistent, high-contrast atomic frequency comb preparation, with a single-component comb lifetime of $277.6 \pm 52.6$s. Together with cavity impedance matching, this yields an on-chip storage efficiency of $23.3 \pm 0.5\%$ for 100-ns storage. The intrinsic electro-optic response of lithium niobate enables frequency-selective storage and routing of retrieved photons at rates up to 20~MHz with inter-channel crosstalk below $10^{-4}$. We further store and retrieve time-energy-entangled telecom photons, violating an entanglement-witness bound by more than 11 standard deviations and thus verifying the quantum nature of the storage process. Our results establish erbium-doped thin-film lithium niobate as a programmable light--matter interface for spectrally multiplexed quantum networks.

Comments
10 pages, 4 figures

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We propose using thin-film lithium niobate on insulator (LNOI) doped with Erbium (Er3+) as a promising solution for implementing large-scale quantum memory. However, the transition from bulk crystals to thin films poses challenges, notably reduced optical depth, which is critical for broad atomic frequency comb memory. To address this, we plan to utilize impedance-matched cavities, increasing the effective optical depth. Furthermore, the cavity would boost the rate of spontaneous emission, increasing the efficiency of spectral hole burning. Our preliminary results reveal high-Q micro-ring resonators (Q≈190k) on Er3+: LNOI, demonstrating a nearly 3.5-fold reduction in the optical lifetime due to cavity resonance.
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 a microsecond using an atomic frequency comb in erbium-doped thin-film lithium niobate, 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 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.
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Atomic frequency combs memories that coherently store optical signals are a key building block for optical quantum computers and quantum networks. Integrating such memories into compact and chip-scale devices is essential for scalable quantum technology, but to date most demonstrations have been in bulk materials or waveguides with large cross-sections, or using fabrication techniques not easily adaptable to wafer scale processing. We demonstrate compact chip-integrated atomic frequency comb storage in rare earth doped thin-film lithium niobate. Our optical memory exhibits a broad storage bandwidth exceeding 100 MHz, and optical storage time of over 250 ns. The enhanced optical confinement in this device structure enables three orders of magnitude reduction in optical power as compared to large ion-diffused waveguides for the same Rabi frequency. These compact atomic frequency comb memories pave the way towards scalable, highly efficient, electro-optically tunable quantum photonic systems that can store and manipulate light on a compact chip.
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