Some Basics

Abstract

In this chapter we review some basics that are of importance in the rest of the book. On the one hand, we consider the construction of classical mean values, and on the other, the quantum mechanical concept of expectation values.

In particular, the difference between the approach of the classical mean value and of the classical probability density function in comparison with the quantum mechanical concept of formation of a “mean”, called expectation value, and quantum mechanical distribution functions defined in Chap. 2 should be clearly recognized. To this end, a glimpse is thrown on the quantum mechanical harmonic oscillator and on the concept of the density operator.