Scalable high-fidelity photon detection using a 20-channel spatially multiplexed SNSPD array

Accurate photon number state resolution is critical for photonic quantum computing architectures to ensure high-fidelity computational outputs. To address this challenge, we have developed a spatially-multiplexed array of waveguide-integrated superconducting-nanowire single-photon detectors (SNSPDs). Waveguide-integrated SNSPDs represent state-of-the-art detector technology, offering operation with low jitter (<30ps), high-count rate (10Mcps), and photon detection efficiency above 90%. Leveraging advances in reliable nanofabrication, we have fabricated SNSPDs using NbN thin films on compact, low-loss photonic SiN circuitry. We present a 20-channel quasi-photon-number-resolving (PNR) detector chip based on a spatially-multiplexed array of eight SNSPDs. The system employs low-loss optical beam splitters to minimize photon pile-up and enables reliable detection of up to three photons. This 20-channel chip represents a significant advancement in scalable, high-performance quantum information processing, paving the way for next-generation quantum computing and communication systems.