Limits to the fundamental measurement accuracy in Josephson junction array voltage intercomparisons

摘要

The dc voltage output from a hysteretic Josephson junction which is locked to an ac frequency source differs from the ideal Josephson relation if the junction drives a current about a closed superconducting circuit. The difference in voltage Dgr;Vfrom two hysteretic Josephson junctions driven in series opposition is proportional to the difference in their driving frequencies Dgr;ohgr; if the junctions are each biased to thenth voltage step. It is shown here, however, that Dgr;Vis systematically smaller than the voltage difference Dgr;V0predicted by the ideal junction relation Dgr;V0=(nℏ/2e)Dgr;ohgr;. If the loop inductance approaches zero, the smallest detectable voltage difference Dgr;V0between two junctions is limited by the intrinsic Josephson inductance. For arrays of more than one junction, however, Dgr;V0remains proportional to the loop inductance.