Axiom of MeasurementThe measurement result is the Eigenvector of the operator, and the Quantum State Vector after measurement collapses to the corresponding Eigenvector.A^∣ϕ⟩=a∣ϕ⟩\hat{A} |\phi\rangle = a |\phi\rangleA^∣ϕ⟩=a∣ϕ⟩