Theory of Quantum Annealing of an Ising Spin Glass

Probing the lowest energy configuration of a complex system by quantum annealing was recently found to be more effective than its classical, thermal counterpart. Comparing classical and quantum Monte Carlo annealing protocols on the random two-dimensional Ising model we confirm the superiority of quantum annealing relative to classical annealing. We also propose a theory of quantum annealing, based on a cascade of Landau-Zener tunneling events. For both classical and quantum annealing, the residual energy after annealing is inversely proportional to a power of the logarithm of the annealing time, but the quantum case has a larger power which makes it fasterComment: RevTex, 8 pages, 3 figure

Band Alignment in Molecular Devices: Influence of Anchoring Group and Metal Work Function

We present periodic Density Functional Theory calculations of the electronic properties of molecular junctions formed by amine-, and thiol-terminated alkane chains attached to two metal (Au, Ag) electrodes. Based on extensive analysis that includes molecular monolayers of varying densities, we establish a relationship between the alignment of the molecular energy levels and the interface dipoles, which shows that the band alignment (BA) in the limit of long, isolated chains is independent of the link group and can be computed from a reference system of non interacting molecule + metal electrodes. The main difference between the amine and thiol linkers is the effective dipole moment at the contact. This is very large, about 4.5 D, for amine linkers, leading to a strong dependence of the BA on the monolayer density and a slow convergence to the isolated molecule limit. Instead, this convergence is fast for S anchors due to the very small, ~ 0.2 D, effective dipoles at the contacts

Hybrid Superconductor-Quantum Point Contact Devices using InSb Nanowires

Proposals for studying topological superconductivity and Majorana bound states in nanowires proximity coupled to superconductors require that transport in the nanowire is ballistic. Previous work on hybrid nanowire-superconductor systems has shown evidence for Majorana bound states, but these experiments were also marked by disorder, which disrupts ballistic transport. In this letter, we demonstrate ballistic transport in InSb nanowires interfaced directly with superconducting Al by observing quantized conductance at zero-magnetic field. Additionally, we demonstrate that the nanowire is proximity coupled to the superconducting contacts by observing Andreev reflection. These results are important steps for robustly establishing topological superconductivity in InSb nanowires

Tratamiento numérico de los Materiales Compuestos

La principal dificultad que se encuentra en el momento de diseñar estructuras con materiales compuestos es la falta de modelos constitutivos que permitan si- mular su comportamiento.  Las técnicas analíticas convencionales utilizadas para el estudio de materiales simples isótropos no resultan adecuadas para el análisis de materiales compuestos. Tampoco ha resultado satisfactoria la representación de un compuesto mediante un único material ortótropo con propiedades del conjunto. Puede observarse en distintas referencias los intentos que ha habido para modelar el comportamiento de materiales compuestos, utilizando la técnica de elementos fi- nitos para el análisis y diseño de estructuras, donde la correlación entre los análisis y los resultados experimentales no resulta satisfactoria (Ali, 1996) (Klintworth y Macmillian, 1992). El proceso de diseño de componentes en materiales compuestos se ha basado, principalmente, en métodos empíricos, observándose en la literatura la ausencia de análisis o simulaciones del comportamiento de materiales compuestos sometidos a niveles de esfuerzos que sobrepasan el límite elástico. &nbsp