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 ωS is close to the resonances given by ωS/ωD=(1/2, 3) / 2 ,(5/2,..., where ωD is the driving frequency. The theoretical prediction for the shift of the bifurcation point, {Δ}μB, which we use as a measure of the stabilization, is {Δ}μB{~}AS², where AS is the perturbation amplitude. We have investigated {Δ}μB as a function of the frequency and the amplitude of the perturbation signal {Δ}μB(ωS,AS) for a model system, the microwave-driven Josephson tunnel junction, and find reasonable agreement between the experimental results and the theory.