Experimental observation of dynamics near the torus-doubling terminal critical point

A nonlinear electronic circuit driven by two signals with golden mean frequency ratio is studied. We have observed different dynamical regimes, including tori, doubled tori, strange nonchaotic attractors, and chaos, which all meet together at the critical point terminating the torus-doubling bifurcation curve (TDT point) in the parameter plane of the system. The parameter plane arrangement, spectra, and portraits of attractors observed in the experiment are in reasonable coincidence with numerical computations for a quasiperiodically forced logistic map, where the TDT critical point originally has been found and studied theoretically [S. Kuznetsov, A. Pikovsky, and U. Feudel, Phys. Rev. E 57, 1585 (1998)].