Geometrical jitter and bolometric regime in photon detection by straight superconducting nanowire

TL;DR

This study directly measures the geometrical jitter in superconducting nanowire photon detectors, revealing how it transitions to a bolometric regime at higher photon fluxes, with detailed analysis of signal propagation speeds.

Contribution

First direct observation of geometrical jitter in straight superconducting nanowires and analysis of its transition to a bolometric regime at increased photon flux.

Findings

Geometrical jitter has a standard deviation of 8.5 ps and FWHM of 29 ps.

Electrical signal propagates at approximately 6.2×10^6 m/s along the nanowire.

Jitter distribution narrows into a Gaussian as photon flux increases, indicating a transition to bolometric detection.

Abstract

We present a direct observation of the geometrical jitter in single photon detection by a straight superconducting nanowire. Differential measurement technique was applied to the 180-{\mu}m long nanowire similar to those commonly used in the technology of superconducting nanowire single photon detectors (SNSPD). A non-gaussian geometrical jitter appears as a wide almost uniform probability distribution (histogram) of the delay time (latency) of the nanowire response to detected photon. White electrical noise of the readout electronics causes broadened, Gaussian shaped edges of the histogram. Subtracting noise contribution, we found for the geometrical jitter a standard deviation of 8.5 ps and the full width at half maximum (FWHM) of the distribution of 29 ps. FWHM corresponds to the propagation speed of the electrical signal along the nanowire of $6.2\times10^{6}$ m/s or 0.02 of the speed of light. Alternatively the propagation speed was estimated from the central frequency of the measured first order self-resonance of the nanowire. Both values agree well with each other and with previously reported values. As the intensity of the incident photon flux increases, the wide probability distribution collapses into a much narrower Gaussian distribution with a standard deviation dominated by the noise of electronics. We associate the collapse of the histogram with the transition from the discrete, single photon detection to the uniform bolometric regime