In this chapter, we treat the basic quantum process of electromagnetic field propagation
through an atomic system in a resonant Fabry-Perot cavity. We obtain the transmission
characteristic of such a cavity, which is a basic element for a quantum heat converter.
When the system is opened only by a population decay and a polarization dephasing,
we get only an optical bistability characteristic. By openness according to the Lindblad-
Sandulescu-Scutaru theory, we get also a coupling through environment between population
and polarization, which, in some conditions, leads to an energy transfer from the disordered
environment to the coherent electromagnetic field. We find that this phenomenon, which
has experimental evidence, is an effect of an atom-atom coupling.
Keywords: pseudo-spin operators, Pauli matrices, Bloch vector, population, polarization,
dipole moment, coupling coefficient, Rabi frequency, decay, dephasing, atomic detuning,
homogeneous broadening, inhomogeneous broadening, Lorentzian shape, Gaussian
shape, optical bistability, nonlinear detuning, saturation, McCall coefficients, cooperativity.
