  In the past few years, the lithium niobate on insulator (LNOI) platform has
revolutionized lithium niobate materials, and a series of quantum photonic
chips based on LNOI have shown unprecedented performances. Quantum frequency
conversion (QFC) photonic chips, which enable quantum state preservation during
frequency tuning, are crucial in quantum technology. In this work, we
demonstrate a low-noise QFC process on an LNOI nanophotonic platform designed
to connect telecom and near-visible bands with sum-frequency generation by
long-wavelength pumping. An internal conversion efficiency of 73% and an
on-chip noise count rate of 900 counts per second (cps) are achieved. Moreover,
the on-chip preservation of quantum statistical properties is verified, showing
that the QFC chip is promising for extensive applications of LNOI integrated
circuits in quantum information. Based on the QFC chip, we construct an
upconversion single-photon detector with the sum-frequency output spectrally
filtered and detected by a silicon single-photon avalanche photodiode,
demonstrating the feasibility of an upconversion single-photon detector on-chip
with a detection efficiency of 8.7% and a noise count rate of 300 cps. The
realization of a low-noise QFC device paves the way for practical chip-scale
QFC-based quantum systems in heterogeneous configurations.
