Direct observation of subpicosecond single-flux-quantum generation in pulse-driven Y-Ba-Cu-O Josephson junctions

We report our time-resolved measurements of switching dynamics of grain-bou ndary, 5-mu m-wide Y-Ba-Cu-O (YBCO) Josephson junctions, excited by 2-ps-wi de electrical pulses optically generated by a voltage-biased, 5-mu m-wide, 10-mu m-long YBCO microbridge. The time-resolved transients were recorded a t 20 K using a subpicosecond cryogenic electro-optic sampling system. The i ntrinsic junction response was separated from the circuit-related feedthrou gh, and we observed both experimentally and in numerical simulations a 0.8- ps-wide, single-flux-quantum (SFQ) pulse, generated by the switching of the junction with the IcRn product equal to similar to 2 mV. At the same time, the measured turn-on delay time was almost three times shorter than that o btained from simulations, questioning applicability of the resistively shun ted tunnel junction model to nonhysteretic, high-temperature superconductin g weak links. Our test structure's power consumption associated with the si ngle SFQ pulse generation was similar to 0.1 mu W, leading to a (switching time)x(dissipated power) product equal to 0.08 aJ. (C) 2000 American Instit ute of Physics. [S0003- 6951(00)01004-4].