A two-level atom interacting with a single mode of quantized electromagnetic radiation is discussed using a new representation in which the atom and the radiation are unified into a single canonical Bose field. At the twice resonance , when the frequency of the original radiation is twice the atomic transition frequency (ω = 2 ), the emergent unified field in the non-interacting atom–field system resembles a free radiation of frequency . This free emergent radiation is further shown to exist in the presence of an interaction which looks similar to the atom–field interaction in the dipole approximation. The one-photon correlation and the population inversion are discussed as the possible means of observing the emergent radiation. The entanglement properties of the emergent radiation are also discussed.
Abstract To describe the interaction of a two-level atom with radiation we shall use a semiclassical treatment, i.e. the radiation is treated as a classical electric field but we use quantum mechanics to treat the atom. From the theory of the interaction with radiation, we will be able to find the conditions for which the equations reduce to a set of rate equations that describe the populations of the atomic energy levels (with a steady-state solution). In particular, for an atom illuminated by broad band radiation, this approach allows us to make a connection with Einstein’s treatment of radiation that was presented in Chapter 1; we shall find the Einstein B coefficient in terms of the matrix element for the transition.