Timing performance of 30-nm-wide superconducting nanowire avalanche photodetectors

We investigated the timing jitter of superconducting nanowire avalanche photodetectors (SNAPs, also referred to as cascade-switching superconducting single-photon detectors) based on 30-nm-wide nanowires. At bias currents (I_B) near the switching current, SNAPs showed sub-35-ps FWHM Gaussian jitter similar to standard 100-nm-wide superconducting nanowire single-photon detectors. At lower values of I_B, the instrument response function (IRF) of the detectors became wider, more asymmetric, and shifted to longer time delays. We could reproduce the experimentally observed IRF time-shift in simulations based on an electrothermal model and explain the effect with a simple physical picture.