We studied the performance of classical and quantum magnetic Otto cycle with a working substance composed of a single quantum dot using the Fock–Darwin model with the inclusion of the Zeeman interaction. Modulating an external/perpendicular magnetic field, in the classical approach, we found an oscillating behavior in the total work extracted that was not present in the quantum formulation.We found that, in the classical approach, the engine yielded a greater performance in terms of total work extracted and efficiency than when compared with the quantum approach. This is because, in the classical case, the working substance can be in thermal equilibrium at each point of the cycle, which maximizes the energy extracted in the adiabatic strokes.

This article studies quantum interference effects and their influence on the electronic transport through a parallel triple quantum-dot system coupled to normal and superconducting leads in the linear response and non-equilibrium regime. We model the system by a triple impurity Anderson Hamiltonian including the Coulomb intra-dot correlations in all quantum-dots. Using the non-equilibrium Green’s function formalism, we calculate the Andreev conductance and the transmittance for energies within the superconductor gap. Our results show that the Andreev reflection spectra, both in the presence and absence of Coulomb interaction, reveal Fano and Dicke-like resonances in analogy to the Fano and Dicke effects in atomic physics. As one of the main results, we obtain that the charge shows abrupt changes due to the Dicke effect.

We investigate bound states in the continuum (BICs) in a hybrid normal-superconducting triple quantum dot system, where the central dot is coupled to two normal leads and the lateral dots are proximity-coupled to superconducting electrodes. Local electron-electron interactions are treated within the Hubbard-I approximation. Finite bias probes Fano-Andreev interference between the direct elastic tunneling path through the central dot and indirect proximity-induced paths involving the lateral dots, revealing an Andreev-type BIC in the symmetric limit and its crossover into a quasi-BIC when lateral-dot detuning mixes the dark and bright sectors. As the bias is swept through the subgap resonances, electron transmission (ET) exhibits sharp antiresonances that evolve into near-zero transmission minima, signaling the transport fingerprints of (quasi-)BICs. We further find a continuous crossover from a Fano-Andreev BIC-supported regime to a Fano-Andreev quasi-BIC regime as the lateral-dot detuning increases. The formation of BICs and quasi-BICs is accompanied by a bias-dependent redistribution of the occupations of the side quantum dots, providing an internal diagnostic directly correlated with the transport signatures of the bound states.