Switching probability of QFP comparators as a function of exciter slew-rate

The current noise (inferred from switching probabilities) of quantum flux parametron (QFP) comparators has been measured as a function of exciter slew rates. It was found that at high slew rates the switching probability follows an error-function distribution quite closely. However, at low slew rates, the distribution resembles a Fermi-Dirac distribution. Good agreement with Monte-Carlo simulations for high slew-rates is seen with a current noise proportional to the Johnson noise of the damping resistors. The current noise decreases with decreasing slew rate and is in good agreement with thermal activation calculations in the limit of slow slew rates.<>