Detector-integrated on-chip QKD receiver for GHz clock rates

Quantum key distribution (QKD) can benefit greatly from photonic integration for low-loss, alignment-free, scalable circuits. Superconducting nanowire single-photon detectors (SNSPDs) are ideal for QKD due to high efficiency, low dark counts, and low jitter. The authors present a QKD receiver chip integrating full photonic circuitry and waveguide-integrated SNSPDs, enabling low dead times and low dark-count rates. They demonstrate a time-bin protocol at 2.6 GHz clock with secret-key rates of 2.5 Mbit/s at 2.5 dB channel attenuation without detector saturation. Broadband 3D polymer couplers allow operation across the telecom band, supporting future wavelength-division multiplexing.