About
A quantum walker applies the Hadamard coin at each step: H|↑⟩=(|↑⟩+|↓⟩)/√2. The walker moves right on |↑⟩, left on |↓⟩. Quantum interference creates a ballistic spread σ~t, vs classical random walk σ~√t. Two peaks emerge from initial state. Decoherence destroys coherence, recovering classical behavior.