Noise and Full Counting Statistics

JOSEPHSON JUNCTIONS and DC-SQUIDs AS DETECTORS OF
HIGH FREQUENCY ELECTRICAL NOISE IN MESOSCOPIC CONDUCTORS

A Josephson junction switches from a superconducting state into a dissipative normal state when approaching its critical current. Hysteretic Josephson junctions can be used as sensitive threshold detector to observe statistics of current, for example shot noise of mesoscopic conductors. Based on our successful experiments on the level of the second moment of noise we have now focused on higher odd moments of current fluctuations. We have performed a set of experiments where, for the first time, the asymmetry of the shot noise current distribution could be detected by a Josephson junction threshold detector. The noise sources were different types of tunnel junctions.

In these measurements shot noise at frequencies up to 50 GHz is observed by the on-chip detector, in contrast to conventional noise measurements where the noise source is connected to a remote detector whose bandwidth is typically much smaller. To explain the observations we developed a theoretical model which combines the effects of resonant excitation of the detector and its adiabatic response to slow current fluctuations. The model agrees with the measurements quantitatively, and simultaneously two models were proposed elsewhere whose results agree with ours within a numerical factor of order unity.