Interference behaviors of resonant transport through a mesoscopic system with ac responses

Time-dependent interference behaviors on currents transporting through a me soscopic system are investigated by using the Keldysh nonequilibrium Green function technique. The system is composed of a quantum dot coupled with tw o electron reservoirs. The electrons in the quantum dot are perturbed by tw o microwave fields (MWFs) through gate. The MWFs cause the energy level spl itting in the quantum dot to form multi-channel for the tunneling current, and these branches of current interfere to produce stable oscillation. The resulting oscillation of current is strongly associated with frequency rela tions between MWFs. The time-dependent current is the consequence of resona nt effects for electrons resonating with quantum dot state and with MWFs. W e present numerical calculations for the cases where the Coulomb interactio n U = 0. Negative temporal current and differential conductance are observe d even if the de bias is not small. We compare the results with correspondi ng quantities in the system perturbed by single MWF.