All eigenstates localize exponentially in 1D random potentials — the localization length ξ ~ 1/disorder²
Anderson (1958): in 1D, any amount of uncorrelated disorder localizes all quantum eigenstates. The wavefunction decays as |ψ(x)| ~ exp(-|x-x₀|/ξ) where ξ ~ (E²-4)·(12/W²)⁻¹ near band center. Transfer matrix method computes exact localization length via Lyapunov exponent.