Picosecond pulses from Josephson junctions: Phenomenological and microscopic analyses

A Josephson junction modeled by the phenomenological current relation together with internal resistance can exhibit pulses in the voltage across the junction when driven by an oscillating current source. These pulses occur singly, in pairs, triplets, etc. with a repetition rate equal to twice the driving frequency. The inclusion of capacitance and inductance generally degrades the pulse characteristics, but attainable values for tunnel junctions are tolerable, with typical parameter values, the pulses have picosecond widths. The phenomenological model becomes suspect on such time scales, however, because typical gap frequencies are just under 10¹²Hz. Preliminary studies based on the microscopic tunnel-junction theory nevertheless show results qualitatively similar to those of the Phenomenological model. The effects of resistor noise and current noise have also been studied. It is concluded that well developed ps voltage pulses can be created in physical Josephson junctions.