Characterization of a Photon-Number Resolving SNSPD Using Poissonian and Sub-Poissonian Light

Photon-number resolving (PNR) single-photon detectors are of interest for a wide range of applications in the emerging field of photon-based quantum technologies. Especially photonic integrated circuits will pave the way for a high complexity and ease of use of quantum photonics. Superconducting nanowire singlephoton detectors (SNSPDs) are of special interest since they combine a high detection efficiency and a high timing accuracy with a high count rate and they can be configured as PNR-SNSPDs. Here, we present a PNR-SNSPD with a four photon resolution suitable for waveguide integration operating at a temperature of 4 K. A high statistical accuracy for the photon number is achieved for a Poissonian light source at a photon flux below 5 photons/pulse with a detection efficiency of 22.7 ± 3 % at 900 nm and a pulse rate frequency of 76 MHz. We demonstrate the ability of such a detector to discriminate a sub-Poissonian from a Poissonian light source.