Effects of parametric perturbations on the onset of chaos in the Josephson-junction model: Theory and analog experiments

We propose an analog apparatus simulating a standard Josephson junction, which allows easy experimental manipulations and measurements. We center our attention on the onset of chaotic responses, in particular on its dependence on the different physical parameters, and we obtain quite good agreement with other existing data. Great attention is also paid to compare the results with the theoretical threshold of chaos we deduce from Melnikov's method: The agreement is globally as good as possible, taking into account the approximations and the validity of the method; in particular, we obtain a description of the behavior of the threshold for small frequencies, and of the important role played by the dc bias term. We also discuss, both theoretically and experimentally, the case of a Josephson junction to which a periodic modulating term has been added