QED of a Two-Level Atom and Photodetection

Abstract

Photodetectors are often modeled by a collection of two-level atoms interacting with a radial, ion field [1.1. In view of the importance of photodetection theory in the framework of different contexts of physics, we have performed an investigation on the QED of a two-level atom. Here we discuss the role of the virtual photons in the process leading to absorption of a single delocalized real photon by a two-level atom, which we fix at the origin of the frame of reference, in the pseudospin S=½ formalism. The interaction with the field is taken in the dipole approximation and it includes counter rotating terms.