Coupled Systems

Abstract

In Chapter 2 the basic equations of motion, Eq. (2.4.15) and the Liouville equation (2.4.16), were derived and applied to the description of interactions between a quantum system and an external classical field. In this chapter we will consider the problem of describing the state of a quantum system which is interacting with other (detected or undetected) quantum systems. This is an important topic and is of central importance to the following discussions in this book. The quantum mechanical theorems which will be introduced provide the basis for the understanding of phenomena such as quantum beats, angular correlations, and spindepolarization effects. In Sections 3.1 and 3.2 we will describe the general theory which is required and in Sections 3.3, 3.4, and 3.5 we will give specific examples which illustrate the meaning and application of the theorems.