Observation of SFQ pulse using HTS sampler

We have succeeded in observing a pico-second current pulse accompanying a single flux quantum (SFQ) using a high- T c superconducting (HTS) sampler. The sampler circuit used in this study, an on-chip sampler, has two pulsers connected to each other at the comparator in one chip. The waveform of an SFQ current pulse from one pulser is measured by using another SFQ pulse from the other pulser as a sampling pulse. We observed a waveform exhibiting two peaks with 5.8 and 1.6 ps widths. Based on these values, we estimated the sampling-pulse width as 2.8 ps, suggesting the potential bandwidth for the HTS sampler of 125 GHz. This value coincides well with the bandwidth expected from the critical current-normal resistance ( I c R n ) product of the Josephson junctions of 1 mV.