 We consider a superposition of number states as the initial state for the field, formula_47, and assume an atom in the excited state is injected into the field.The initial state of the system is

Since the formula_49 are stationary states of the field-atom system, then the state vector for times
formula_50 is just given by

The Rabi oscillations can readily be seen in the sin and cos functions in the state vector.Different periods occur for different number states of photons.