Dark counts initiated by macroscopic quantum tunneling in NbN superconducting photon detectors

TL;DR

This study demonstrates that macroscopic quantum tunneling occurs in NbN superconducting photon detectors at low temperatures, contributing to dark counts, and is evidenced by saturation in switching current distribution variability.

Contribution

It provides experimental evidence of macroscopic quantum tunneling in quasi-2D NbN superconducting strips used for photon detection, analyzed through the Kurkijarvi-Garg model.

Findings

Saturation of switching distribution standard deviation around 2 K

Confirmation of escape temperature saturation at low temperatures

Macroscopic quantum tunneling contributes to dark counts in detectors

Abstract

We perform measurements of the switching current distributions of three w = 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijarvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors.