Three temperature regimes in superconducting photon detectors: Quantum, thermal and multiple phase-slips as generators of dark counts

Scientific Reports. 2015. Vol. 5. P. 10174.

Murphy A., Semenov A., Korneev A., Korneeva Y., Goltsman G., Bezryadin A.

We perform measurements of the switching current distributions of three w nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter of 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 2K. We analyze our results using the Kurkijärvi-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. At the highest temperatures the system enters a multiple phase-slip regime. In this range single phase-slips are unable to produce dark counts and the fluctuations in the switching current are reduced.

Keywords: Quantum, single-photon detectors, multiple phase-slips, thermal phase-slips