Description
Superconducting Nanowire Single Photon Detectors (SNSPDs) represent a highly promising and versatile detection technology for applications in quantum optics, photonic quantum computing, quantum key distribution, and beyond. Commercial implementations achieve high detection efficiencies alongside low timing jitter and short reset times. However, a key limitation of standard SNSPD readout schemes is their intrinsic lack of photon-number resolution.
We combine principal component analysis with a new readout technique to investigate the photon-number resolving capabilities in both commercial and experimental SNSPDs. Our analysis shows that the photon-number information is captured in a single principal component that approximates the time derivative of the average response trace. This suggests that optimal photon-number resolution can be achieved by projecting onto the mean derivative of the detector pulse. This can be done with moderate hardware requirements in terms of both sample rate (5 GSample/sec) and analog bandwidth (3 GHz), is more resilient to noise compared to current methods, and could be implemented in an FPGA, giving a highly scalable solution for photon counting.