Frequent measurement freezes quantum evolution; P(t) = cos²(Ωt/2)
The Quantum Zeno Effect: projecting onto |0⟩ at rate n per unit time gives survival probability P ≈ cos²ⁿ(Ωt/2n) → 1 as n→∞. At intermediate measurement rates the anti-Zeno effect accelerates decay when the measurement cycle matches transition frequencies. The Zeno subspace is the subspace stabilized by frequent projection.