  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.
