Position Sensitive Response of a Single-Pixel Large-Area SNSPD

TL;DR

This paper investigates how the response of large-area superconducting nanowire single-photon detectors varies with photon position, number, and bias current, revealing position-sensitive effects and a bimodal rise time distribution.

Contribution

It introduces a model explaining position-dependent response in large-area SNSPDs and characterizes the bimodal distribution of pulse rise times based on incident photon parameters.

Findings

Bimodal distribution of pulse rise times observed.

Slow rise times increase with larger optical spots and fewer photons.

Dark counts resemble low-bias, small-photon pulses.

Abstract

Superconducting nanowire single photon detectors (SNSPDs) are typically used as single-mode-fiber-coupled single-pixel detectors, but large area detectors are increasingly critical for applications ranging from microscopy to free-space quantum communications. Here, we explore changes in the rising edge of the readout pulse for large-area SNSPDs as a function of the bias current, optical spot size on the detector, and number of photons per pulse. We observe a bimodal distribution of rise times and show that the probability of a slow rise time increases in the limit of large spot sizes and small photon number. In the limit of low bias currents, the dark-count readout pulse is most similar to the combined large spot size and small-photon-number bright-count readout pulse. These results are consistent with a simple model of traveling microwave modes excited by single photons incident at varying positions along the length of the nanowire.