Quantum description of the input and output electromagnetic fields in a polarizable confined system

The effect on the electromagnetic modes of the interaction with a polarizable medium confined along one direction is studied in the framework of a full quantum-mechanical theory. A general quantum-mechanical method of computing the scattered electromagnetic field in confined systems is presented. A precise link between the semiclassical and the quantum theory of polaritons in confined systems is established. The method is applied to the case of a semiconductor quantum well embedded in infinite barriers. The experimental situation of a classical traveling light wave partly reflected and partly transmitted by the well is found to correspond to a particular coherent photon-exciton mixed state. Simple analytical expressions are obtained for experimental quantities such as transmission and reflectivity. The polariton quanta are identified as the ''physical'' photons detected in photon counting experiments.