Construction of Detection Electronics to Measure Superconducting-to-Normal Switching Events in a Josephson Junction

Wide interest in superconductor-based quantum computing motivates our investigation of one  of the mechanisms driving the readout of the quantum state of a Josephson junction. Escape of a Josephson phase particle from the zero-voltage state of a current-biased, hysteretic Josephson junction has been studied experimentally, in agreement with Kramers theory for the escape of a Brownian particle from a potential well. The effect has been investigated in devices made from single-gap superconductors such as Al and Nb, high-Tc superconductors, and multi-gap superconductors such as MgB2[1]. We report on progress in building electronics that allows physics undergraduates to perform similar experiments using a 2 Kelvin cryocooler, potentially on multi-gap superconductors. The electronics consist of current ramp bias circuit and a Schmidt trigger detection circuit that amplifies and measures the switching of voltage of a Josephson junction, and a universal time interval counter to measure switching statistics. This work is being performed by a team of undergraduates.

[1] S. Carabello, et al., J. Appl. Phys. 120, 123904 (2016).