Frequency noise in hysteretic resistive SQUIDs

We present measurements of hysteretic resistive SQUIDs (R-SQUIDs) as a function of the hysteresis parameter β L =2 πLI c/ Φ 0. Varying β L in situ from 15 to 45, we observe quasiperiodic peaks in frequency noise which decrease toward the thermal limit with increasing temperature. We have developed a model illustrating the dynamics of the two characteristic time scales: Josephson phase oscillations and catastrophic transitions in phase. From this model, an intuitive energy picture emerges wherein low thermal energy is shown to promote trapping in false minima leading to excess frequency noise. The energy model further illustrates that confusion between degenerate branch solutions results in quasiperiodic noise peaks.