Dynamics and decoherence in non ideal Thouless quantum motors.

BUSTOS-MARÚN, RAÚL A.; HORACIO M. PASTAWSKI; FERNÁNDEZ, LUCAS J.

San Carlos de Bariloche

Workshop; ICTP School and Workshop on driven quantum systems; 2016

Different proposals for adiabatic quantum motors (AQMs) driven by DC currents have recently attracted considerable interest. However, the systemsstudied were often based on simplified models with highly ideal conditions and where the environment was neglected. Here we investigate the performance (dynamics, efficieny and output power) of a prototypical AQM, the Thouless motor. We study the deviations of this AQMs with respect to their simplified model based on a linearized Hamiltonian whichneglects decoherence and the effect of the edgesthe system. In order to correctly account for the environmental effects on this type of AQMS we extended our previous theory of decoherence in current induced forces to account for multiple site-dependent decoherent events. We provide analytical expressions for the current induced forces, friction coefficients and self correlation functions of the forces. We also prove that the model fulfill fluctuation dissipation theorem as well as Onsager?s reciprocity relations. We find that decoherence drastically reduce the efficiencythe motor mainly due to the increase in conductance, while its effect on the output power is not so important. Interestingly, this type of AQM shows a memory effect of its  quantum character, where even in the presence of high decoherence ratio it is possibledistinguish the effects of quantum mechanics on the efficiency. We also find that the effect of the edgesthe system on the scattering matrix induces an additional conservative force that can dramatically alterits dynamics. We show that, within a certain rangevoltages and friction coefficients, the system presents hysteresis with two limiting voltages that switch on-off its movement depending on its previous history.