Perturbed period-doubling bifurcation. II. Experiments on Josephson junctions

We present experimental results on the effect of periodic perturbations on a driven, dynamic system that is close to a period-doubling bifurcation. In the preceding article a scaling law for the change of stability of such a system was derived for the case where the perturbation frequency ${\mathrm{\omega }}_{\mathit{S}}$ is close to the resonances given by ${\mathrm{\omega }}_{\mathit{S}}$/${\mathrm{\omega }}_{\mathit{D}}$=(1/2, 3) / 2 ,(5/2,..., where ${\mathrm{\omega }}_{\mathit{D}}$ is the driving frequency. The theoretical prediction for the shift of the bifurcation point, Δ${\mathrm{\mu }}_{\mathit{B}}$, which we use as a measure of the stabilization, is Δ${\mathrm{\mu }}_{\mathit{B}}$∼${\mathit{A}}_{\mathit{S}}^2$, where ${\mathit{A}}_{\mathit{S}}$ is the perturbation amplitude. We have investigated Δ${\mathrm{\mu }}_{\mathit{B}}$ as a function of the frequency and the amplitude of the perturbation signal Δ${\mathrm{\mu }}_{\mathit{B}}$(${\mathrm{\omega }}_{\mathit{S}}$,${\mathit{A}}_{\mathit{S}}$) for a model system, the microwave-driven Josephson tunnel junction, and find reasonable agreement between the experimental results and the theory.