Quantum mechanics is the theory for small physical systems.It does provide a mathematical and conceptual framework for the development of laws that a physical system must obey.It has several basic postulates.The first is about state space,in which quantum mechanics takes place.The second is about the evolution of quantum system.The third is about quantum measurement,which describes what an experimentalist will obtain when he/she observes the system.These three postulates provide a connection between the physical world and the mathematical formalism of quantum mechanics [1].