Studies of return maps, chaos, and phase-locked states in a current-driven Josephson-junction simulator

Measurements of return maps, power spectra, Poincar\'e sections, phase-space trajectories, and current-voltage characteristics have been made with an electronic simulator which satisfies the same differential equation as a current-driven Josephson junction. The results suggest that the return map for this system is a circle map. A large number of phase-locked subharmonic modes have been found by measuring the power spectra and phase-space portraits, and intermittent chaos is normally observed in regions between the stable modes. Hopping between states is believed to play an important role in the low-voltage region. Self-similarity structure in the subharmonic modes and three observed sequences are in agreement with the theoretical work by Jensen et al.