  We have exactly solved a model of equidistant cascade four-level system
interacting with a single-mode radiation field both semiclassically and quantum
mechanically by exploiting its similarity with Jaynes-Cummings model. For the
classical field, it is shown that the Rabi oscillation of the system initially
in the first level (second level) is similar to that of the system when it is
initially in the fourth level (third level). We then proceed to solve the
quantized version of the model where the dressed state is constructed by using
a six parameter four-dimensional matrix and show that the symmetry exhibited in
the Rabi oscillation of the system for the semiclassical model is completely
destroyed on the quantization of the cavity field. Finally we have studied the
collapse and revival of the system for the cavity field-mode in a coherent
state to discuss the restoration of symmetry and its implication is discussed.
