Effects of energy-level quantization on the supercurrent decay of Josephson junctions

We present measurements of the supercurrent decay in high quality Nb/AlOx/N b Josephson junctions which show evidence of energy-level quantization with in the washboard potential describing the junction. The effect of discrete energy levels leads to oscillations in the rate of escape from the zero vol tage state as a function of the bias current, observed at different tempera tures. The oscillation spacing fits that expected from the energy level qua ntization. Moreover, a fit with the quantum theory allows us to derive inte resting conclusions about the effective dissipation of the system at low te mperatures. [S0163-1829(99)08701-9].