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.
@article{arxiv.1410.7689,
title = {Dark counts initiated by macroscopic quantum tunneling in NbN superconducting photon detectors},
author = {A. Murphy and A. Semenov and A. Korneev and Yu. Korneeva and G. Gol'tsman and A. Bezryadin},
journal= {arXiv preprint arXiv:1410.7689},
year = {2014}
}