Radio-frequency based monitoring of small supercurrents

We consider the applicability of the established rf readout technique, which allows to obtain the supercurrent-phase relation of a Josephson element from impedance measurements in the phase-biased regime. In experiments on Nb-based single and double tunnel junctions, we demonstrate that this method holds even if the Josephson coupling energy is smaller than the thermal energy. Compared with conventional current-voltage measurements, we evaluate the rf technique to be favorable in particular for investigations of small supercurrents in low-capacitance Josephson elements. (C) 2001 American Institute of Physics.