According to the postulates of quantum mechanics [1–5] the state of the system ψ(0) at t = 0 is related to the state of the system ψ (t) at any other time t through: ψ(t)=U(t)ψ(0) where U(t) Is an evolution operator. The reader interested In a rigorous mathematical treatment of the evolution operators and their properties is referred to Refs. 4 and 5. A comprehensive summary is given in Apendix I. It immediately follows from the properties of U(t) that ψ(0)=U+(t)ψ(t) where U† is the adjoint of U.