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The RCSJ (resistively and capacitively shunted junction) model: β(d²φ/dt²) + (dφ/dt) + sin(φ) = I_dc + I_ac·cos(Ωt). The phase φ is the superconducting phase difference. At low drive, the junction phase-locks (periodic). At high drive amplitude, the system exhibits period-doubling cascades and chaos. Left: phase portrait (φ mod 2π vs dφ/dt). Right: time series of the voltage (dφ/dt).