Different proposals for adiabatic quantum motors (AQMs) driven by DC currents have recently attracted considerable interest. However, the systems studied are often based on simplified models with highly ideal conditions where the environment is neglected. Here, we investigate the performance (dynamics, efficiency, and output power) of a prototypical AQM, the Thouless motor. To include the effect of the surroundings on this type of AQMs, we extended our previous theory of decoherence in current-induced forces (CIFs) to account for spatially distributed decoherent processes. We provide analytical expressions that account for decoherence in CIFs, friction coefficients and the self-correlation functions of the CIFs. We prove that the model is thermodynamically consistent and we find that decoherence drastically reduces the efficiency of the motor mainly due to the increase in conductance, while its effect on the output power is not much relevant. The effect of decoherence on the current-induced friction depends on the length of the system, reducing the friction for small systems while increasing it for long ones. Finally, we find that reflections of the electrons at the boundary of the system induce additional conservative forces that affect the dynamics of the motor. In particular, this results in the hysteresis of the system and a voltage dependent switching.

Current induced forces are not only related with the discrete nature of electrons but also with its quantum character. It is natural then to wonder about the effect of decoherence. Here, we develop the theory of current induced forces including dephasing processes and we apply it to study adiabatic quantum motors (AQMs). The theory is based on Büttiker's fictitious probe model which here is reformulated for this particular case. We prove that it accomplishes fluctuation-dissipation theorem. We also show that, in spite of decoherence, the total work performed by the current induced forces remains equal to the pumped charge per cycle times the voltage. We find that decoherence affects not only the current induced forces of the system but also its intrinsic friction and noise, modifying in a non trivial way the efficiency of AQMs. We apply the theory to study an AQM inspired by a classical peristaltic pump where we surprisingly find that decoherence can play a crucial role by triggering its operation. Our results can help to understand how environmentally induced dephasing affects the quantum behavior of nano-mechanical devices.

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an instantaneous scattering matrix approach to unveil the critical role of wave interference in radiative heat transfer. We find that appropriately designed adiabatic pumping cycling near diabolic singularities can dramatically enhance the efficiency of the directional energy transfer. We confirm our results using a realistic electronic circuit set-up.arXiv:1906.00305v1 [physics.optics]

Decoherent transport in mesoscopic and nanoscopic systems can be formulated in terms of the D'Amato-Pastawski (DP) model. This generalizes the Landauer-Büttiker picture by considering a distribution of local decoherent processes. However, its generalization for multi-terminal setups is lacking. We first review the original two-terminal DP model for decoherent transport. Then, we extend it to a matrix formulation capable of dealing with multi-terminal problems. We also introduce recursive algorithms to evaluate the Green's functions for general banded Hamiltonians as well as local density of states, effective conductances and voltage profiles. We finally illustrate the method by analyzing two problems of current relevance. 1) Assessing the role of decoherence in a model for phonon lasers (SASER). 2) Obtaining the classical limit of Giant Magnetoresistance from a spin-dependent Hamiltonian. The presented methods should pave the way for computationally demanding calculations of transport through nanodevices, bridging the gap between fully coherent quantum schemes and semiclassical ones.

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