Discrete quantum motors

We investigate dissipative quantum motion of a particle in a discrete periodic asymmetric lattice coupled to an Ohmic bath and subjected to a nonbiased oscillatory field. In the adiabatic forcing regime we find analytically external forcing rectification resulting in a motor mechanism through persistent current creation. The direction and intensity of the motor operation is controlled by the competing mechanisms of discreteness induced Stark localization and phonon assisted ratchet delocalization. Maximal current of either sign is predicted at a parameter dependent characteristic temperature.