DSpace Community:
http://hdl.handle.net/10261/135
Sun, 13 Jul 2014 03:55:58 GMT
20140713T03:55:58Z
The Channel Image
http://digital.csic.es:80/retrieve/56927/fotoiem2.jpg
http://hdl.handle.net/10261/135

Diagonal ladders: A class of models for strongly coupled electron systems
http://hdl.handle.net/10261/99528
Title: Diagonal ladders: A class of models for strongly coupled electron systems
Authors: Sierra, Germán; MartínDelgado, Miguel Ángel; White, S. R.; Scalapino, D.J.; Dukelsky, Jorge
Abstract: We introduce a class of models defined on ladders with a diagonal structure generated by np plaquettes. The case np=1 corresponds to the necklace ladder and has remarkable properties that are studied using density matrix renormalizationgroup and recurrent variational ansatzes. The antiferromagnetic Heisenberg (AFH) model on this ladder is equivalent to the alternating spin1/spin1/2 AFH chain, which is known to have a ferromagnetic ground state (GS). For doping 1/3 the GS is a fully doped (1,1) stripe with the holes located mostly along the principal diagonal while the minor diagonals are occupied by spin singlets. This state can be seen as a Mott insulator of localized Cooper pairs on the plaquettes. A physical picture of our results is provided by a tpJptd model of plaquettes coupled diagonally with a hopping parameter td. In the limit td →∞ we recover the original tJ model on the necklace ladder while for a weak hopping parameter the model is easily solvable. The GS in the strong hopping regime is essentially an >on link> Gutzwiller projection of the weak hopping GS. We generalize the tpJptd model to diagonal ladders with np≥1 and the twodimensional square lattice. We use in our construction concepts familiar in statistical mechanics such as medial graphs and Bratelli diagrams. © 1999 The American Physical Society.
Mon, 07 Jul 2014 10:01:50 GMT
http://hdl.handle.net/10261/99528
20140707T10:01:50Z

Density matrix renormalization group study of ultrasmall superconducting grains
http://hdl.handle.net/10261/99509
Title: Density matrix renormalization group study of ultrasmall superconducting grains
Authors: Dukelsky, Jorge; Sierra, Germán
Abstract: We apply the density matrix renormalization group (DMRG) method to the BCS pairing Hamiltonian which describes ultrasmall superconducting grains. Our version of the DMRG uses the particle (hole) states around the Fermi level as the system block (environment). We observed a smooth logarithmiclike crossover between the few electron regime and the BCSbulk regime. © 1999 The American Physical Society.
Mon, 07 Jul 2014 09:00:28 GMT
http://hdl.handle.net/10261/99509
20140707T09:00:28Z

Theoretical and experimental study of the acetohydroxamic acid protonation: The solvent effect
http://hdl.handle.net/10261/99487
Title: Theoretical and experimental study of the acetohydroxamic acid protonation: The solvent effect
Authors: García, Begoña; Ibeas, S.; Leal, J. M.; Senent Díez, María Luisa; Niño, A.; MuñozCaro, C.
Abstract: The mechanism of the protonation of acetohydroxamic acid is investigated comparing experimental results and ab initio calculations. Experimentally, the UV spectral curves were recorded at different temperatures, at constant dioxane/water concentration, and at very high concentrations of strong mineral acids. The process is followed by monitoring the changes in the UV curves with increasing acid concentration. The molecular structures and the solvation energies were calculated with the RHF, B3LYP, and MP2 methods. The solvent is treated as a continuum of uniform dielectric constant. The isolated molecule of acetohydroxamic acid exhibits two protonation sites, the carbonyl oxygen and the nitrogen atom. In dioxane/water mixture, the RHF calculations predict the existence of a third cation of low stability, where the proton is bonded to the OH oxygen. With the MP2 ab initio calculations, the free energies of the formation processes in solution of the two most stable cations, CH3COHNHOH+ (O3H + ) and CH3CONH2OH+ have been evaluated to be  160.2 kcal mol1 and  157.6 kcal mol1. The carbonyl site is the most active center in solution and in the gas phase. The carbonyl site is also the most active center in the UV measurements. Experimentally, the ionization constant was found to be pKO3H+ =  2.21 at 298.15 K, after the elimination of the medium effects using the CoxYates equation for hight acidity levels. Experiments and ab initio calculations indicate that KO3H+ decreases with the temperature.
Mon, 07 Jul 2014 07:40:48 GMT
http://hdl.handle.net/10261/99487
20140707T07:40:48Z

Lattice scars: surviving in an open discrete billiard
http://hdl.handle.net/10261/97882
Title: Lattice scars: surviving in an open discrete billiard
Authors: FernándezHurtado, Victor; MurPetit, Jordi; GarciaRipoll, Juan Jose; Molina, Rafael A.
Abstract: We study quantum systems on a discrete bounded lattice (lattice billiards). The statistical properties of their spectra show universal features related to the regular or chaotic character of their classical continuum counterparts. However, the decay dynamics of the open systems appear very different from the continuum case, their properties being dominated by the states in the band center. We identify a class of states ('lattice scars') that survive for infinite times in dissipative systems and that are degenerate at the center of the band. We provide analytical arguments for their existence in any bipartite lattice, and give a formula to determine their number. These states should be relevant to quantum transport in discrete systems, and we discuss how to observe them using photonic waveguides, cold atoms in optical lattices, and quantum circuits.
Description: Editorially selected as an "IoP Select" article. Part of "Focus on Coherent Control of Complex Quantum Systems". 14 pag, 67 refs, 2 videos.
Fri, 06 Jun 2014 08:22:22 GMT
http://hdl.handle.net/10261/97882
20140606T08:22:22Z

Collective modes of a trapped iondipole system
http://hdl.handle.net/10261/97876
Title: Collective modes of a trapped iondipole system
Authors: MurPetit, Jordi; GarciaRipoll, Juan Jose
Abstract: We study a simple model consisting of an atomic ion and a polar molecule trapped in a single setup, taking into consideration their electrostatic interaction. We determine analytically their collective modes of excitation as a function of their masses, trapping frequencies, distance, and the molecule’s electric dipole moment. We then discuss the application of these collective excitations to cool molecules, to entangle molecules and ions, and to realize twoqubit gates between them. We finally present a numerical analysis of the possibility of applying these tools to study magnetically ordered phases of twodimensional arrays of polar molecules, a setup proposed to quantumsimulate some strongly correlated models of condensed matter.
Description: 13 pags, 74 refs.
Fri, 06 Jun 2014 08:05:59 GMT
http://hdl.handle.net/10261/97876
20140606T08:05:59Z

Phase Stabilization of a Frequency Comb using Multipulse Quantum Interferometry
http://hdl.handle.net/10261/97874
Title: Phase Stabilization of a Frequency Comb using Multipulse Quantum Interferometry
Authors: Cadarso, Andrea; MurPetit, Jordi; GarciaRipoll, Juan Jose
Abstract: From the interaction between a frequency comb and an atomic qubit, we derive quantum protocols for the determination of the carrierenvelope offset phase, using the qubit coherence as a reference, and without the need of frequency doubling or an octave spanning comb. Compared with a trivial interference protocol, the multipulse protocol results in a polynomial enhancement of the sensitivity O(1/N^2) with the number N of laser pulses involved. We specialize the protocols using optical or hyperfine qubits, Lambda schemes, and Raman transitions, and introduce methods where the reference is another phasestable cw laser or frequency comb.
Description: 4 páginas + 9 páginas de material suplementario
Fri, 06 Jun 2014 07:54:05 GMT
http://hdl.handle.net/10261/97874
20140606T07:54:05Z

Mecánica y Dinámica Molecular con Forcite en Materials Studio
http://hdl.handle.net/10261/97724
Title: Mecánica y Dinámica Molecular con Forcite en Materials Studio
Authors: Ramos, Javier
Abstract: Forcite es una herramienta avanzada para realizar cálculos de mecánica molecular clásica, permite el cálculo de energías, optimizaciones geométricas y propiedades dinámicas de sistemas moleculares y periódicos. Forcite dispone de una gran variedad de campos de fuerzas diferentes que permite el cálculo de casi cualquier sistema. Además proporciona una gran flexibilidad para generar modelos optimizados y comparar sus energías de forma rápida y sencilla a través de la interfaz gráfica de Materials Studio.
En este “webinar”, se hará una breve introducción a la teoría y a las características fundamentales del módulo Forcite en Materials Studio. Después, se presentarán un par de ejemplos completos a modo de tutorial para que los asistentes vean la sencillez y capacidad de esta herramienta.
Wed, 04 Jun 2014 09:47:03 GMT
http://hdl.handle.net/10261/97724
20140604T09:47:03Z

Nearly degenerate neutrinos, supersymmetry and radiative corrections
http://hdl.handle.net/10261/97063
Title: Nearly degenerate neutrinos, supersymmetry and radiative corrections
Authors: Casas, J.A.; Espinosa, José Ramón; Ibarra, A.; Navarro, I.
Abstract: If neutrinos are to play a relevant cosmological rôle, they must be essentially degenerate with a mass matrix of the bimaximal mixing type. We study this scenario in the MSSM framework, finding that if neutrino masses are produced by a seesaw mechanism, the radiative corrections give rise to mass splittings and mixing angles that can accommodate the atmospheric and the (large angle MSW) solar neutrino oscillations. This provides a natural origin for the Δm2 sol ≪ Δm2 atm hierarchy. On the other hand, the vacuum oscillation solution to the solar neutrino problem is always excluded. We discuss also in the SUSY scenario other possible effects of radiative corrections involving the new neutrino Yukawa couplings, including implications for triviality limits on the Majorana mass, the infrared fixed point value of the top Yukawa coupling, and gauge coupling and bottomtau unification. © 2000 Elsevier Science B.V. All rights reserved.
Thu, 22 May 2014 07:48:22 GMT
http://hdl.handle.net/10261/97063
20140522T07:48:22Z

Exact study of the effect of level statistics in ultrasmall superconducting grains
http://hdl.handle.net/10261/96855
Title: Exact study of the effect of level statistics in ultrasmall superconducting grains
Authors: Sierra, Germán; Dukelsky, Jorge; Dussel, G. G.; Von Delft, J.; Braun, F.
Abstract: The reduced BCS model that is commonly used for ultrasmall superconducting grains has an exact solution worked out long ago by Richardson in the context of nuclear physics. We use it to check the quality of previous treatments of this model, and to investigate the effect of level statistics on pairing correlations. We find that the groundstate energies are on average somewhat lower for systems with nonuniform than uniform level spacings, but both have an equally smooth crossover from the bulk to the fewelectron regime. In the latter, statistical fluctuations in groundstate energies strongly depend on the grain's electron number parity. ©2000 The American Physical Society.
Mon, 19 May 2014 10:49:28 GMT
http://hdl.handle.net/10261/96855
20140519T10:49:28Z

Be (βp), a quasifree neutron decay?
http://hdl.handle.net/10261/96647
Title: Be (βp), a quasifree neutron decay?
Authors: Riisager, Karsten; Borge, M. J. G.; Briz, J.A.; Carmona Gallardo, M.; Gottberg, A.; Tengblad, Olof; Winkler, S.
Abstract: We have observed β−β−delayed proton emission from the neutronrich nucleus 11Be by analyzing a sample collected at the ISOLDE facility at CERN with accelerator mass spectrometry (AMS). With a branching ratio of (8.3±0.9)⋅10−6(8.3±0.9)⋅10−6 the strength of this decay mode, as measured by the BGTBGTvalue, is unexpectedly high. The result is discussed within a simple singleparticle model and could be interpreted as a quasifree decay of the 11Be halo neutron into a singleproton state.
Description: Riisager, Karsten et al.
Wed, 14 May 2014 07:42:09 GMT
http://hdl.handle.net/10261/96647
20140514T07:42:09Z