Dark Bell states in tunnel-coupled spin qubits

We investigate the dynamical purification of maximally entangled electron states by transport through coupled quantum dots. Under resonant ac driving and coherent tunneling, even-parity Bell states perform Rabi oscillations that decouple from the environment, leading to a dark state. The two electrons remain spatially separated, one in each quantum dot. We propose configurations where this effect will prove as antiresonances in transport spectroscopy experiments.Comment: 5 pages, 4 figures + supplementary information. Published versio

Spin-polarized currents in double and triple quantum dots driven by ac magnetic fields

We analyze transport through both a double quantum dot and a triple quantum dot with inhomogeneous Zeeman splittings in the presence of crossed dc and ac magnetic fields. We find that strongly spin-polarized current can be achieved by tuning the relative energies of the Zeeman-split levels of the dots, by means of electric gate voltages: depending on the energy level detuning, the double quantum dot works either as spin-up or spin-down filter. We show that a triple quantum dot in series under crossed dc and ac magnetic fields can act not only as spin-filter but also as spin-inverter.Comment: 8 pages, 7 figures, published versio

Floquet Majorana Fermions in superconducting quantum dots

We consider different configurations of ac driven quantum dots coupled to superconductor leads where Majorana fermions can exist as collective quasiparticles. The main goal is to tune the existence, localization and properties of these zero energy quasiparticles by means of periodically driven external gates. In particular, we analyze the relevance of the system and driving symmetry. We predict the existence of different sweet spots with Floquet Majorana fermions in configurations where they are not present in the undriven system.Comment: Contribution to the Physica E special issue on "Frontiers in quantum electronic transport" - in memory of Markus B\"uttike

Fourier transform analysis of irradiated Weiss oscillations

We present a theoretical approach to study the effect of microwave radiation on the magnetoresistance of a one-dimensional superlattice. In our proposal the magnetoresistance of a unidirectional spatial periodic potential (superlattice), is modulated by microwave radiation due to an interference effect between both, space and time-dependent potentials. The final magnetoresistance will mainly depend on the spatial period of the superlattice and the radiation frequency. %Then, by tuning either the spatial period of the superlattice or the radiation %frequency, the magnetoresistance can be strongly modified. We consider an approach to study these effects based on the fast Fourier transform of the obtained magnetorresistance profiles in function of the inverse of the magnetic field. Based on this theory we propose the design of a novel radiation sensor for the Terahertz band.} % We first study the FFT of the system for each potential individually. Then we study jointly the FFT of the system when the two types of potentials are simultaneously acting.Comment: 5 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:0808.237

Radiation-induced resistance oscillations in a 2D hole gas: a demonstration of a universal effect

We report on a theoretical insight about the microwave-induced resistance oscillations and zero resistance states when dealing with p-type semiconductors and holes instead of electrons. We consider a high-mobility two-dimensional hole gas hosted in a pure Ge/SiGe quantum well. Similarly to electrons we obtain radiation-induce resistance oscillations and zero resistance states. We analytically deduce a universal expression for the irradiated magnetoresistance, explaining the origin of the minima positions and their $1/4$ cycle phase shift. The outcome is that these phenomena are universal and only depend on radiation and cyclotron frequencies. We also study the possibility of having simultaneously two different carriers driven by radiation: light and heavy holes. As a result the calculated magnetoresistance reveals an interference profile due to the different effective masses of the two types of carriers.Comment: 9 pages and 9 figure