High resolution superconducting single flux quantum comparator for sub   kelvin temperatures
  A design of subkelvin single flux quantum (SFQ) circuits with reduced power dissipation and additional cooling of shunt resistors for superconducting qubit control circuits has been developed and characterized. We demonstrate operation of SFQ comparators with current resolution of 40 nA at 2 GHz sampling rate. Due to improved cooling the electron temperature in shunt resistors of a SFQ comparator is below 50 mK when the bath temperature is about 30 mK. 
A.M. Savin, J.P. Pekola, T. Holmqvist, J. Hassel, L. Gr\"onberg, P.   Helist\"o, A. Kidiyarova-Shevchenko