Current plateaus of nonadiabatic charge pump: Multiphoton assisted processes

We report a theoretical investigation of quantum parametric charge pump in the nonadiabatic regime at finite pumping frequency and finite driving amplitude. A general and closed-form expression for pumped current is derived in the form of a continuous fraction reflecting the multiphoton processes which are found to play an important role. Our nonperturbative theory predicts a remarkable plateau structure in the pumped current due to these multiphoton assisted processes in a double-barrier quantum well involving only a single pumping potential. A current reversal is found as the resonant level of the pump crosses the Fermi energy of the leads.