Picosecond switching dynamics of a Josephson tunnel junction

The authors previously reported (D.R. Dykaar et al., 1987) switching measurements of a tunnel junction excited by photogenerated picosecond current pulses. The junction was found to switch from the zero- to the finite-voltage regime for subcritical current pulses, and the results were modeled with a critical charge concept. It is shown that in addition to pulse charge, pulse risetime is a critical parameter in determining the junction response. Simulations have been performed using exponentially rising and failing pulses to simulate the experimentally measured waveform. Significant deviations from DC behavior have been found. Pulse risetime has been found be the parameter which causes the onset of the observed chaos in these devices. Pulse falltime has no effect, which is consistent with the critical risetime interpretation