The Chirikov Standard Map
The standard map is the simplest Hamiltonian system that exhibits the full transition from order to chaos. At K = 0, every orbit lies on an invariant torus — a closed curve in phase space. As K increases, resonant tori break into island chains (Poincaré-Birkhoff theorem), while irrational tori persist — these are the KAM tori, guaranteed by the Kolmogorov-Arnold-Moser theorem.
At K ≈ 0.9716 (the Greene critical value), the last KAM torus — with winding number equal to the golden ratio — is destroyed. Above this threshold, chaotic orbits can diffuse across the entire phase space.
This transition from integrable order to deterministic chaos is fundamental to celestial mechanics, plasma confinement, particle accelerators, and the stability of quantum computing gates.