Role of coherence in quantum-dot-based nanomachines within the Coulomb blockade regime

Abstract

During the last decades, quantum dots within the Coulomb blockade regime of transport have been proposed as essential building blocks for a wide variety of nanomachines. This includes thermoelectric devices, quantum shuttles, quantum pumps, and even quantum motors. However, in this regime, the role of quantum mechanics is commonly limited to provide energy quantization while the working principle of the devices is ultimately the same as their classic counterparts. Here, we study quantum-dot-based nanomachines in the Coulomb blockade regime, but in a configuration that resembles the quantum mechanics' paradigmatic experiment: the doubleslit. We show that the coherent superposition of states appearing in this configuration can be used as the basis for different forms of "true" quantum machines. We analyze the efficiency of these machines against different non-equilibrium sources (bias voltage, temperature gradient, and external driving) and the factors that limit it, including decoherence and the role of the different orders appearing in the adiabatic expansion of the charge/heat currents.

Fluctuation-induced currents in suspended graphene nanoribbons: Adiabatic quantum pumping approach

“…Adiabatic quantum pumping arises from the first-order correction (in a frequency expansion) to the adiabatic approximation of an observable, the current in our case. Technical details of its derivation can be found among different contexts [27,35,39,55,56]. In the present case, the adiabatic approximation and its first-order correction will be valid when the time it takes for the electrons to move along the lattice sites is much shorter than the time it takes for the Hamiltonian to change.…”