  A quantum system comprising of a monochromatic electromagnetic field coupled
to a SQUID ring with sinusoidal non-linearity, is studied. A magnetostatic flux
$\Phi_{x}$ is also threading the SQUID ring, and is used to control the
coupling between the two systems. It is shown that for special values of
$\Phi_{x}$ the system is strongly coupled. The time evolution of the system is
studied. It is shown that exchange of energy takes place between the two modes
and that the system becomes entangled. A second quasi-classical model that
treats the electromagnetic field classically is also studied. A comparison
between the fully quantum mechanical model with the electromagnetic field
initially in a coherent state and the quasi-classical model, is made.
