Electron transmission through an ac biased quantum point contact

We consider a transmission through the potential relief created by a split gate constriction (quantum point contact). Simultaneously, dc and ac voltages V-up(t)=V-0+V-1 cos omega t and V-dw(t)=V-0+V-1 cos(omega t+theta) are applied to the gates. We show numerically that the in-phase ac voltages (theta=0) smear the conductance steps of the stationary conductance, while the antiphase ac voltages (theta=pi) only shift the conductance steps. Moreover, computation of currents in probing wires connected cross to the time-periodic quantum point contact reveals a net current for theta not equal 0,pi. This implies that the Schrodinger equation described by the electron transport under the effect of the time-periodic long electrodes is equivalent to the transmission in the crossed effective magnetic and electric fields, where the in-plane magnetic field b similar to theta is directed along the transport axis and the electric field e similar to omega is directed perpendicular to the plane of electron transport. Then the vector exb gives rise to the galvanomagnetic current directed cross to the electron transport.