Microscopic model of critical current noise in Josephson junctions

We present a simple microscopic model to show how fluctuating two-level systems in a Josephson junction tunnel barrier of thickness L can modify the potential energy of the barrier and produce critical current noise spectra. We find low frequency 1/f noise that goes as L-5. Our values are in good agreement with recent experimental measurements of critical current noise in Al/AlOx/Al Josephson junctions. We also investigate the sensitivity of the noise on the nonuniformity of the tunnel barrier.