Direct measurement of the Josephson supercurrent in an ultrasmall Josephson junction

We have measured the supercurrent flowing through a nonhysteretic, ultrasmall, volta-c-biased Joseph son junction. In contrast with experiments performed so far on hysteretic Josephson junctions, we find a supercurrent peak whose maximum I-s max increases as the temperature T decreases. The asymptotic T = 0 value of I-s max agrees with the junction Arnbegaokar-Baratoff critical current, as predicted by theory.