20GHz pulse position modulation with a low jitter Photon Number Resolving Superconducting Nanowire Single Photon Detector

The emergence of high performance Superconducting Nanowire Single Photon Detectors (SNSPDs) is pivotal to the development of future quantum and photon-starved classical communication systems. These detectors achieve low jitter, high efficiency, and photon number resolution (PNR) all in a single device. We demonstrate the use of a differential readout Niobium Nitride SNSPD in a 20GHz pulse position modulation (PPM) communication protocol. The detector uses differential readout as well as impedance matching tapers for efficient coupling of energy out of the nanowire. Furthermore, the tapers induce photon number dependent distortions on the rising edge of the readout pulse. Therefore timetagging these pulses at a constant voltage convolves photon arrival time and photon number information. We demonstrate a method for measuring RF pulse slope that may be used to (1) measure photon number per optical pulse and (2) extract a low jitter photon arrival time measurement that is uncorrelated with photon number. Our photon-starved communication demonstration therefore fully exploits the lower jitter of a new SNSPD type to run at high rate, while managing its complex manifestation of photon number resolution.