Appearance of chaos in a superconducting ring closed by a Josephson junction

Stochastic behavior of the main part of a high-frequency squId, a superconducting ring closed with a Josephson junction, is observed experimentally. The corresponding current--voltage and amplitude--frequency characteristics and the spectral density of the noise are presented. It is shown that when the parameters of the hf squId are varied continuously, the dynamic system changes smoothly from periodic oscillations to stochastic oscillations in the hysteresis regime. Complicated changes in the oscillations occur near this transition: the appearance of ''1/f noise,'' transformation of its spectral density in the high frequency range, and periodic dependence on the external (signal) flux. The results obtained demonstrate that the hf squId is a convenient object for direct detailed study of stochastic instability in real dynamic systems