ABSTRACT
This chapter presents a systematic treatment of quantum theory in terms of six groups of postulates on the fundamental properties of quantum systems: postulate on the description of pure states, postulate on the description of observables and their values, postulate on the transition from classical to quantum systems, postulates on the probabilistic relationship between states and observables, postulates on the time evolution of the system and postulate on states after measurement. It extends the basic theory to discuss mixed states, superselection rules and many-particle systems. The chapter presents a brief discussion of conceptual problems in quantum mechanics. A maximum amount of information about the system corresponds to a set of simultaneously measured values of a complete set of discrete observables of the system. Such an amount of information characterises a state of the system. States characterised by such a maximum amount of information about the system are called pure states.
