Quantum Systems

Abstract

So far we have been dealing with classical systems whose dimensions are macroscopic. In this chapter we wish to consider systems that must be described by means of quantum theory. Let us look at a few examples of systems where quantum effects play a role. The first example is provided by the laser. Its individual atoms must be treated by quantum mechanics and in it the field is produced by quantum mechanical events, namely those of spontaneous and stimulated emission. Therefore, a rigorous theory of the laser must be based on quantum mechanics. In the previous chapters we based our laser theory on the so-called semiclassical treatment which can be derived from the fully quantum mechanical treatment by a method called quantum classical correspondence which will not be pursued here.