Quantum frequency conversion and single-photon detection with lithium niobate nanophotonic chips

The lithium niobate on insulator (LNOI) platform has revolutionized lithium niobate materials, and a series of quantum photonic chips have exhibited unprecedented performances. Quantum frequency conversion (QFC) that enables quantum state preservation during frequency conversion is crucial in quantum technology. This work demonstrates a low-noise QFC process on the LNOI nanophotonic platform, connecting telecom and near-visible bands. An internal conversion efficiency of 73% and an on-chip noise count of 900 counts per second (cps) are achieved. Furthermore, the preservation of quantum statistical properties is verified, indicating the QFC chip's promise for extensive applications of LNOI integrated circuits in quantum information. Based on this chip, we constructed an upconversion single-photon detector with a detection efficiency of 8.7% and a noise of 300 cps, paving the way to integrated on-chip single-photon detection. The realization of a low-noise QFC device also provide a pathway for practical chip-scale QFC-based quantum systems in heterogeneous configurations.