Josephson Junction Chaos

d²φ/dt² + (1/Q)dφ/dt + sin(φ) = I_dc + I_ac·cos(ωt)

Poincaré Section (stroboscopic)

Phase velocity dφ/dt vs time

The Josephson junction is a quantum tunneling device. AC drive + nonlinear sin(φ) term produces deterministic chaos. The Poincaré section samples (φ mod 2π, dφ/dt) once per drive period — chaotic attractors appear as fractal point clouds.