Fiber-integrated Quantum Frequency Conversion for Long-distance Quantum Networking

TL;DR

This paper presents a fiber-integrated quantum frequency converter that efficiently links quantum nodes to telecom channels, enabling scalable long-distance quantum communication with high fidelity.

Contribution

It introduces a compact, low-noise, high-efficiency fiber-based QFC system with a theoretical model for entanglement fidelity in quantum networks.

Findings

Achieved ~9% conversion efficiency with low pump noise.

SNRs of 12.3, 43.9, and 117.8 at different photon rates.

Maintains over 52% entanglement fidelity over 100 km.

Abstract

Signal photons emitted by quantum nodes typically fall outside the low-loss telecom window of optical fibers, leading to severe transmission losses. Quantum frequency conversion (QFC) offers an effective optical interface that bridges quantum nodes with telecom-band channels, enabling long-distance quantum communication. In this work, we demonstrate a compact, fiber-integrated QFC system with low noise and a high signal-to-noise ratio (SNR). Using a periodically poled lithium niobate (PPLN) waveguide, input photons at 637.2 nm are down-converted to telecom photons at 1588.3 nm. Our system achieves a total conversion efficiency of approximately 9%, with pump-induced noise suppressed to 154 Hz. For input photon rates of 32.7, 118.0, and 327.7 kHz, the corresponding SNRs are 12.3, 43.9, and 117.8, respectively. We further develop a theoretical model to simulate the entanglement fidelity between nitrogen-vacancy (NV) center spins and the frequency-converted telecom photons. At the emission rate of an NV center, our QFC system maintains an expected fidelity exceeding 52% over a transmission distance of 100 km. These findings highlight the potential of our QFC system for scalable, long-distance quantum networking.