Stochastic resonance: noise actually improves signal detection in nonlinear systems.
Kramers rate r_K = (Δ/2π)·exp(−2Δ/σ²). Resonance when r_K ≈ ω/2 — noise synchronizes transitions with the signal.
SNR peaks at intermediate noise — "the right amount of randomness." Demonstrated in neurons, climate, quantum systems.