QUANTUM DECOHERENCE

Bloch sphere coherence decay · density matrix evolution · environment coupling
θ: — φ: —
Purity: —
|ρ_01|: —
Decoherence: quantum superposition leaks into environment entanglement. Off-diagonal ρ_{01} → 0. Purity tr(ρ²) → 1/2. The Bloch vector shrinks inside the sphere.