Pair shot noise and zero-point Johnson noise in Josephson junctions

Measured transition rates out of the superconducting state of low-current-density 1m Nb Josephson junctions at temperatures down to 3 mK are 5 to 11 orders of magnitude below the predicted rates due to pair shot noise. The lowest-temperature measurements are also inconsistent with activation due to zero-point Johnson noise. © 1981 The American Physical Society.