We report the measurement results of the low-power single-flux-quantum (SFQ) circuits below 20 mK using a dilution refrigerator. We have been developing the SFQ circuits using a lowered critical current density process (250 A/cm2) and low-voltage design (0.1–0.5 mV) toward digital signal processing near superconductor quantum bits. So far, we have designed several basic SFQ cells, including wiring elements, flip-flops, and logic gates, using the four Nb planarized layer process and obtained the correct operation at 300 mK. In this study, we tested several SFQ circuits aiming to evaluate the operation at the mixing chamber stage of a dilution refrigerator. Our experimental results show that there was almost no change of device parameters, such as critical current values of Josephson junctions, or operating margins of the basic cells between 300 mK and 16 mK.
Tanaka et al. (Thu,) studied this question.