Lifetime of the zero-voltage state in Josephson tunnel junctions

We describe an experimental investigation of fluctuations in the measured value of the critical current in Josephson tunnel junctions. The lifetime τ of the zero-voltage state against spontaneous transitions to a nonzero-voltage state is derived from these measurements. The range of τ covered by these measurements runs from 10^-1 to 10^-7 sec, with τ decreasing approximately exponentially with increasing current bias. Both thermal-noise-limited and extrinsic-noise-limited situations have been observed. In associated experiments the maximum critical current of these Sn-Sn-oxide-Sn juntions is found to be reduced from the value predicted by weak-coupling theory by a factor of ≈0.92, presumably by strong-coupling effects.