Quantum Signatures in Superconducting-to-Normal Switching Experiments on a Multigap Superconducting Junction

We review the results of our tunneling spectroscopy experiments¹ which demonstrated microwave resonant activation in a multi-gap superconductor. We had measured histograms of superconducting-to-normal switching events in hybrid Josephson heterojunctions (MgB₂/I/Pb and MgB₂/I/Sn) at sub-Kelvin temperatures. When microwaves were coupled to the junctions, we observed peaks superposed on the histograms - features consistent with microwave resonant activation. This demonstrates microwave resonant activation in a novel superconducting multigap system where one superconducting electrode is multi-gap and the other superconducting electrode is single-gap. In this system, we have observed signatures of quantum behavior such as the Lorentzian shape of the escape rate enhancement, a saturation in the width of the switching current distribution at low temperatures, and evidence of multi-photon transitions.

¹ S. Carabello, J. Lambert, J. Mlack, W. Dai, Q. Li, K. Chen, D. Cunnane, X. X. Xi, and R. C. Ramos, "Microwave resonant activation in hybrid single-gap/two-gap Josephson tunnel junctions,"J. Appl. Phys. 120, 123904 (2016)