High-resolution superconducting single-flux quantum comparator for sub-Kelvin temperatures

A design of sub-Kelvin single-flux quantum (SFQ) circuits with reduced power dissipation and additional cooling of shunt resistors has been developed and characterized. The authors demonstrate operation of SFQ comparators with current resolution of 40nA at 2GHz sampling rate. Due to improved cooling the electron temperature in shunt resistors of a SFQ comparator is below 50mK when the bath temperature is about 30mK.