  In this article, we consider fixed spin-1/2 particles interacting through the
quantized electromagnetic field in a constant magnetic field. We give
approximate evolutions of coherent states. This uses spins-photon classical
Hamiltonian mechanics. These approximations enable to derive that the
approximate average fields and spins follow Maxwell-Bloch equations with a
current density coming from spins. In addition, we obain a law concerning the
evolution of the approximate average number of photons. Next, we provide
stationary points of the spins-photon Hamiltonian when the spin particles
belong to an orthogonal plane to the constant magnetic field. This allows for
the construction of quasimodes with spins colinear to the constant magnetic
field. Finally, a quasimode with an arbitrary high accuracy is built up and its
first order radiative correction is computed.
