We have shown theoretically that the coupling of two harmonic oscillators interacting indendently with a common field is a natural consequence of the elastic scattering from the quentized E.M. field.
The number operators of each oscillator at Heisenberg picture are described in terms of those at time t=0 and then they appear to be coupled each other with the assistance of the field.
Hence we can justify the ab initio presence of cooperative states in such systems frequently assumed in the studies of superradiance phenomena.
