Renormalization of Optical Excitations in Molecules near a Metal Surface

The lowest electronic excitations of benzene and a set of donor-acceptor molecular complexes are calculated for the gas phase and on the Al(111) surface using the many-body Bethe-Salpeter equation (BSE). The energy of the charge-transfer excitations obtained for the gas phase complexes are found to be around 10% lower than the experimental values. When the molecules are placed outside the surface, the enhanced screening from the metal reduces the exciton binding energies by several eVs and the transition energies by up to 1 eV depending on the size of the transition-generated dipole. As a striking consequence we find that close to the metal surface the optical gap of benzene can exceed its quasiparticle gap. A classical image charge model for the screened Coulomb interaction can account for all these effects which, on the other hand, are completely missed by standard time-dependent density functional theory.Comment: 4 pages, 3 figures; revised versio

Analytical model of non-Markovian decoherence in donor-based charge quantum bits

We develop an analytical model for describing the dynamics of a donor-based charge quantum bit (qubit). As a result, the quantum decoherence of the qubit is analytically obtained and shown to reveal non-Markovian features: The decoherence rate varies with time and even attains negative values, generating a non-exponential decay of the electronic coherence and a later recoherence. The resulting coherence time is inversely proportional to the temperature, thus leading to low decoherence below a material dependent characteristic temperature.Comment: 19 pages, 3 figure

Graphene on metals: a Van der Waals density functional study

We use density functional theory (DFT) with a recently developed van der Waals density functional (vdW-DF) to study the adsorption of graphene on Al, Cu, Ag, Au, Pt, Pd, Co and Ni(111) surfaces. In constrast to the local density approximation (LDA) which predicts relatively strong binding for Ni,Co and Pd, the vdW-DF predicts weak binding for all metals and metal-graphene distances in the range 3.40-3.72 \AA. At these distances the graphene bandstructure as calculated with DFT and the many-body G$_0$W$_0$ method is basically unaffected by the substrate, in particular there is no opening of a band gap at the $K$-point.Comment: 4 pages, 3 figure

Phonon-induced entanglement dynamics of two donor-based charge quantum bits

The entanglement dynamics of a pair of donor-based charge qubits is obtained in analytical form. The disentanglement is induced by off resonant scattering of acoustical phonons in the semiconductor host. According to our results a rather unusual recovery of entanglement occurs that depends on the geometrical configuration of the qubits. In addition, for large times a non-vanishing stationary entanglement is predicted. For the cases of one and two initial excitations a simple kinetic interpretation allows for an adequate analysis of the observed dynamics. Our results also reveal a direct relation between the disentanglement rate and the inter-donor decoherence rates

Computational Design of Chemical Nanosensors: Metal Doped Carbon Nanotubes

We use computational screening to systematically investigate the use of transition metal doped carbon nanotubes for chemical gas sensing. For a set of relevant target molecules (CO, NH3, H2S) and the main components of air (N2, O2, H2O), we calculate the binding energy and change in conductance upon adsorption on a metal atom occupying a vacancy of a (6,6) carbon nanotube. Based on these descriptors, we identify the most promising dopant candidates for detection of a given target molecule. From the fractional coverage of the metal sites in thermal equilibrium with air, we estimate the change in the nanotube resistance per doping site as a function of the target molecule concentration assuming charge transport in the diffusive regime. Our analysis points to Ni-doped nanotubes as candidates for CO sensors working under typical atmospheric conditions

Impurity Effects in Two-Electron Coupled Quantum Dots: Entanglement Modulation

We present a detailed analysis of the electronic and optical properties of two-electron quantum dots with a two-dimensional Gaussian confinement potential. We study the effects of Coulomb impurities and the possibility of manipulate the entanglement of the electrons by controlling the confinement potential parameters. The degree of entanglement becomes highly modulated by both the location and charge screening of the impurity atom, resulting two regimes: one of low entanglement and other of high entanglement, with both of them mainly determined by the magnitude of the charge. It is shown that the magnitude of the oscillator strength of the system could provide an indication of the presence and characteristics of impurities that could largely influence the degree of entanglement of the system.Comment: Regular Article (Journal of Physics B, in press), 9 pages, 10 figure

Conocimientos y actitudes ante la Voluntad Anticipada en profesionales de la salud del Centro Médico “Lic. Adolfo López Mateos”, Toluca, México

Introducción: La Voluntad Anticipada es una declaración mediante la cual una persona mayor de edad, con capacidad mental suficiente y libremente, expone las instrucciones que se deben tener en cuenta respecto a la atención sanitaria que desea recibir en situaciones en las cuales no pueda ya expresar personalmente su voluntad. Objetivo: Determinar el nivel de conocimientos y actitudes que tienen los profesionales de la salud de Centro Médico “Lic. Adolfo López Mateos” con respecto a la Ley de Voluntad Anticipada del Estado de México. Método y materiales: Se aplicaron 265 encuestas que incluían el conocimiento y la actitud que tienen los profesionales de la salud sobre la Ley de Voluntad Anticipada del Estado de México. Resultados: El grupo mayoritario abarcó de 25-29 años con el 31%, el turno mayoritario fue el de la Jornada Especial con 34%, el 60% de los encuestados fueron mujeres y 40% hombres, el 94% no había leído la Ley de Voluntad Anticipada inscrita en la gaceta oficial del Gobierno del Estado de México y el 6% restante respondió afirmativamente. Conclusiones: La mayoría de los y las profesionales de salud refirieron no conocer la Ley inscrita en la gaceta oficial, lo que significa que hace falta difusión y promoción del tema; a pesar de eso, tuvieron una posición favorable hacia la voluntad anticipada y demostraron tener noción sobre lo tratad

Calculation of quantum discord for qubit-qudit or N qubits

Quantum discord, a kind of quantum correlation, is defined as the difference between quantum mutual information and classical correlation in a bipartite system. It has been discussed so far for small systems with only a few independent parameters. We extend here to a much broader class of states when the second party is of arbitrary dimension d, so long as the first, measured, party is a qubit. We present two formulae to calculate quantum discord, the first relating to the original entropic definition and the second to a recently proposed geometric distance measure which leads to an analytical formulation. The tracing over the qubit in the entropic calculation is reduced to a very simple prescription. And, when the d-dimensional system is a so-called X state, the density matrix having non-zero elements only along the diagonal and anti-diagonal so as to appear visually like the letter X, the entropic calculation can be carried out analytically. Such states of the full bipartite qubit-qudit system may be named "extended X states", whose density matrix is built of four block matrices, each visually appearing as an X. The optimization involved in the entropic calculation is generally over two parameters, reducing to one for many cases, and avoided altogether for an overwhelmingly large set of density matrices as our numerical investigations demonstrate. Our results also apply to states of a N-qubit system, where "extended X states" consist of (2^(N+2) - 1) states, larger in number than the (2^(N+1) - 1) of X states of N qubits. While these are still smaller than the total number (2^(2N) - 1) of states of N qubits, the number of parameters involved is nevertheless large. In the case of N = 2, they encompass the entire 15-dimensional parameter space, that is, the extended X states for N = 2 represent the full qubit-qubit system.Comment: 6 pages, 1 figur