Introduction

Abstract

The method which is the subject of this book originated from the early times of quantum mechanics. In 1926, Schrödinger [1] first introduced a system of nonorthogonal wave functions to describe nonspreading wave packets for quantum oscillators. A few years later, in the famous book by von Neumann [2], an important subset of these wave functions was considered, which was related to the partitioning of the phase plane of a one-dimensional dynamical system into regular cells. Von Neumann used this subset to investigate the coordinate and momentum measurement processes in quantum theory. For a considerable time these ideas of the eminent scientists did not attract undue attention. It was only in the early sixties that the approach was thoroughly studied [3–6]. Glauber [7,8] named the states invented by Schrödinger the coherent states (CS) and showed that they are adequate to describe a coherent laser beam in the framework of quantum theory.