The quantum dynamics of a three-level equidistant ladder-type atom placed in an optical resonator is investigated. Both atomic transitions are pumped by intense laser light and couples to the cavity single-mode electromagnetic field. Under the laser pumping, the atomic energy levels split and transition side-bands appear. Here, one reports a destructive quantum interference effect, which is observed whereas the cavity frequency is tuned to the most or less energetic side-bands.     The model is analytically described via the system Hamiltonian and Master Equation (ME) formalism. The Hamiltonian is defined by the atom and cavity free terms, the semi-classical interaction term of the atom with the pumping lasers and the interaction term of the atom with the quantized cavity field. The ME includes the cavity damping term and the atomic spontaneous emission terms. The mentioned terms are generally known and described in various textbooks [1]. The full analytic approach and a detailed discussion of the observed effects are published in [2].     The solving of the ME is done as follows. The splitting of the energy levels is analytically expressed via a dressed-state transformation which is applied to the Hamiltonian and the ME. Under a convenient choice of representation, i.e., the interaction picture for the dressed-state expressions, the temporally oscillating Hamiltonian terms are split according to the side-bands’ frequencies. Therefore, when the cavity resonates with one of the sidebands, a rotating wave approximation may be applied to the Hamiltonian. Thus, the Hamiltonian is brought to a form that allows the solving of the ME. More precisely, the ME is solved by projecting it in the system basis [2].     Once the model is solved, we investigate the quantum dynamics of the cavity field via the mean photon number of the field and its second-order correlation function. We obtain a destructive interference effect when the cavity field completely vanishes although the atom is pumped and spontaneously emits photons in all other directions except the cavity. Moreover, the second-order correlation function suggests a completely decoupling of the atom from the cavity as the empty cavity is find to be in equilibrium with the surrounding vacuum under the interferences effect. Finally, the analysis of the Hamiltonian expression allows explaining the interference effect as the superposition of two indistinguishable amplitudes of the dressed atom-cavity interaction.   Acknowledgment  The author is thankful to Dr. hab. M. A. Macovei for his contribution to the presented study.