Introduction

Abstract

The concept of quantum coherence applied to light-matter interactions is central to the present book. It unifies a whole spectrum of coherent optical phenomena observed in different quantum solid-state systems. Quantum coherence is naturally invoked in the description of the quantum dynamics, or the time evolution of quantum systems, under an external perturbation. It has long been recognised that an intimate relationship exists between quantum coherence and quantum correlations and the latter can be used in a rigorous definition of quantum coherence. Depending on the number of coherence conditions satisfied by a succession of correlation functions describing the system, the degree of coherence ranges from various orders of incomplete coherence to full coherence, when the successive correlators satisfy an infinite number of coherence conditions. Dynamical processes in quantum systems are wave phenomena, subject to constructive and destructive interferences and therefore the ultimate goal to achieve control of quantum dynamics requires active manipulation of constructive and destructive interferences.