Probing the Hotspot Interaction Length in NbN Nanowire Superconducting Single-Photon Detectors

TL;DR

This paper investigates the maximum interaction length for photon detection in NbN nanowire SSPDs, revealing a length of approximately 23 nm that aligns with quasiparticle cloud size, advancing understanding of detection mechanisms.

Contribution

It provides a direct measurement of the hotspot interaction length in NbN SSPDs, linking it to quasiparticle cloud dimensions, which was previously not quantitatively established.

Findings

Interaction length is approximately 23 nm.

The measured length matches quasiparticle cloud size.

Detection efficiency depends on nanowire length.

Abstract

We measure the maximal distance at which two absorbed photons can jointly trigger a detection event in NbN nanowire superconducting single photon detector (SSPD) microbridges by comparing the one-photon and two-photon efficiency of bridges of different overall lengths, from 0 to 400 nm. We find a length of $23 \pm 2$ nm. This value is in good agreement with to size of the quasiparticle cloud at the time of the detection event.