We have studied the electron transport through a quantum dot coupled to three
leads in the presence of external microwave fields supplied to different parts
of the considered mesoscopic system. Additionally, we introduced a possible
nonresonant tunneling channels between leads. The quantum dot charge and
currents were determined in terms of the appropriate evolution operator matrix
elements and under the wide band limit the analytical formulas for
time-averaged currents and differential conductance were obtained. We have also
examined the response of the considered system on the rectangular-pulse
modulation imposed on different quantum dot-leads barriers as well as the
time-dependence of currents flowing in response to suddenly removed (or
included) connection of a quantum dot with one of the leads.Comment: 34 pages, 12 figure