  The exact solutions of the equation for a composite scalar particle which
possesses electric and magnetic polarizabilities are found in an external
uniform static magnetic field parallel to the direction of propagation of the
quantized electromagnetic wave. As a particular case, the relativistic coherent
states of a particle in the field of photons were considered. When the average
photon number trends to infinity, the solution tends to the solution
corresponding to the external classical electromagnetic wave with circular
polarization.
