Abstract
We present an analytical expression for the response of a transient spectrum to a single-Cooper-pair box biased by a classical voltage and irradiated by a single-mode quantized field. The exact solution of the model is obtained, by means of which we analyze the analytic form of the fluorescence spectrum using the transitions among the dressed states of the system. An interesting relation between the fluorescence spectrum and the dynamical evolution is found when the initial field states are prepared in binomial states.