Selective coherent destruction of tunneling in a quantum-dot array

The coherent manipulation of quantum states is one of the main tasks required in quantum computation. In this paper we demonstrate that it is possible to control coherently the electronic position of a particle in a quantum-dot array. By tuning an external ac electric field we can selectively suppress the tunneling between dots, trapping the particle in a determined region of the array. The problem is treated non-perturbatively by a time-dependent Hamiltonian in the effective mass approximation and using Floquet theory. We find that the quasienergy spectrum exhibits crossings at certain field intensities that result in the selective suppression of tunneling.Comment: 4 pages, 5 figures, submitted to PRB Rapid Com

Nonlocal Spin Transport as a Probe of Viscous Magnon Fluids

Magnons in ferromagnets behave as a viscous fluid over a length scale, the momentum-relaxation length, below which momentum-conserving scattering processes dominate. We show theoretically that in this hydrodynamic regime viscous effects lead to a sign change in the magnon chemical potential, which can be detected as a sign change in the nonlocal resistance measured in spin transport experiments. This sign change is observable when the injector-detector distance becomes comparable to the momentum-relaxation length. Taking into account momentum- and spin-relaxation processes, we consider the quasiconservation laws for momentum and spin in a magnon fluid. The resulting equations are solved for nonlocal spin transport devices in which spin is injected and detected via metallic leads. Because of the finite viscosity we also find a backflow of magnons close to the injector lead. Our work shows that nonlocal magnon spin transport devices are an attractive platform to develop and study magnon-fluid dynamics

Search for the Higgs Boson H20H_2^0 at LHC in 3-3-1 Model

We present an analysis of production and signature of neutral Higgs boson ($H_{2}^{0}$) on the version of the 3-3-1 model containing heavy leptons at the Large Hadron Collider. We studied the possibility to identify it using the respective branching ratios. Cross section are given for the collider energy, $\sqrt{s} =$ 14 TeV. Event rates and significances are discussed for two possible values of integrated luminosity, 300 fb$^{-1}$ and 3000 fb$^{-1}$.Comment: 17 pages 7 figures. arXiv admin note: substantial text overlap with arXiv:1205.404

Structural properties of GaAsN/GaAs quantum wells studied at the atomic scale by cross-sectional scanning tunnelling microscopy

The nitrogen distribution in GaAsNGaAs quantum wells _QWs_ grown by molecular beam epitaxy is studied on the atomic scale by cross-sectional scanning tunneling microscopy. No nitrogen clustering is observed in the range of N contents studied _between 1.0% and 2.5%, as measured by counting the individual N atoms inside the QW_. Nevertheless, the upper interface roughness increases with the amount of N. A residual N concentration in the GaAs barriers is found, which strongly increases with the amount of N in the QW

Strong spin relaxation length dependence on electric field gradients

We discuss the influence of electrical effects on spin transport, and in particular the propagation and relaxation of spin polarized electrons in the presence of inhomogeneous electric fields. We show that the spin relaxation length strongly depends on electric field gradients, and that significant suppression of electron spin polarization can occur as a result thereof. A discussion in terms of a drift-diffusion picture, and self-consistent numerical calculations based on a Boltzmann-Poisson approach shows that the spin relaxation length in fact can be of the order of the charge screening length.Comment: 4 pages, 3 figures, to be presented at PASPSI