Graded-index optical fiber emulator of an interacting three-atom system: illumination control of particle statistics and classical non-separability

We show that a system of three trapped ultracold and strongly interacting atoms in one-dimension can be emulated using an optical fiber with a graded-index profile and thin metallic slabs. While the wave-nature of single quantum particles leads to direct and well known analogies with classical optics, for interacting many-particle systems with unrestricted statistics such analoga are not straightforward. Here we study the symmetries present in the fiber eigenstates by using discrete group theory and show that, by spatially modulating the incident field, one can select the atomic statistics, i.e., emulate a system of three bosons, fermions or two bosons or fermions plus an additional distinguishable particle. We also show that the optical system is able to produce classical non-separability resembling that found in the analogous atomic system.Comment: 14 pages, 5 figure

Ab initio wavefunction based methods for excited states in solids: correlation corrections to the band structure of ionic oxides

Ab initio wavefunction based methods are applied to the study of electron correlation effects on the band structure of oxide systems. We choose MgO as a prototype closed-shell ionic oxide. Our analysis is based on a local Hamiltonian approach and performed on finite fragments cut from the infinite solid. Localized Wannier functions and embedding potentials are obtained from prior periodic Hartree-Fock (HF) calculations. We investigate the role of various electron correlation effects in reducing the HF band gap and modifying the band widths. On-site and nearest-neighbor charge relaxation as well as long-range polarization effects are calculated. Whereas correlation effects are essential for computing accurate band gaps, we found that they produce smaller changes on the HF band widths, at least for this material. Surprisingly, a broadening effect is obtained for the O 2p valence bands. The ab initio data are in good agreement with the energy gap and band width derived from thermoreflectance and x-ray photoemission experiments. The results show that the wavefunction based approach applied here allows for well controlled approximations and a transparent identification of the microscopic processes which determine the electronic band structure

Higgs bosons near 125 GeV in the NMSSM with constraints at the GUT scale

We study the NMSSM with universal Susy breaking terms (besides the Higgs sector) at the GUT scale. Within this constrained parameter space, it is not difficult to find a Higgs boson with a mass of about 125 GeV and an enhanced cross section in the diphoton channel. An additional lighter Higgs boson with reduced couplings and a mass <123 GeV is potentially observable at the LHC. The NMSSM-specific Yukawa couplings lambda and kappa are relatively large and tan(beta) is small, such that lambda, kappa and the top Yukawa coupling are of order 1 at the GUT scale. The lightest stop can be as light as 105 GeV, and the fine-tuning is modest. WMAP constraints can be satisfied by a dominantly higgsino-like LSP with substantial bino, wino and singlino admixtures and a mass of ~60-90 GeV, which would potentially be detectable by XENON100.Comment: 20 pages, 14 figure

Correlations in a two-dimensional Bose gas with long range interactions

We study the correlations of two-dimensional dipolar excitons in coupled quantum wells with a dipole -- dipole repulsive interaction. We show that at low concentrations, the Bose degeneracy of the excitons is accompanied by strong multi-particle correlations and the system behaves as a Bose liquid. At high concentration the particles interaction suppresses quantum coherence and the system behaves similar to a classical liquid down to a temperature lower than typical for a Bose gas. We evaluate the interaction energy per particle and the resulting blue shift of the exciton luminescence that is a direct tool to measure the correlations. This theory can apply to other systems of bosons with extended interaction.Comment: 11 pages including 2 figure

Dynamical generalization of a solvable family of two-electron model atoms with general interparticle repulsion

Holas, Howard and March [Phys. Lett. A {\bf 310}, 451 (2003)] have obtained analytic solutions for ground-state properties of a whole family of two-electron spin-compensated harmonically confined model atoms whose different members are characterized by a specific interparticle potential energy u($r_{12}$). Here, we make a start on the dynamic generalization of the harmonic external potential, the motivation being the serious criticism levelled recently against the foundations of time-dependent density-functional theory (e.g. [J. Schirmer and A. Dreuw, Phys. Rev. A {\bf 75}, 022513 (2007)]). In this context, we derive a simplified expression for the time-dependent electron density for arbitrary interparticle interaction, which is fully determined by an one-dimensional non-interacting Hamiltonian. Moreover, a closed solution for the momentum space density in the Moshinsky model is obtained.Comment: 5 pages, submitted to J. Phys.

Energy gaps in quantum first-order mean-field-like transitions: The problems that quantum annealing cannot solve

We study first-order quantum phase transitions in models where the mean-field traitment is exact, and the exponentially fast closure of the energy gap with the system size at the transition. We consider exactly solvable ferromagnetic models, and show that they reduce to the Grover problem in a particular limit. We compute the coefficient in the exponential closure of the gap using an instantonic approach, and discuss the (dire) consequences for quantum annealing.Comment: 6 pages, 3 figure

On the upper bound of the electronic kinetic energy in terms of density functionals

We propose a simple density functional expression for the upper bound of the kinetic energy for electronic systems. Such a functional is valid in the limit of slowly varying density, its validity outside this regime is discussed by making a comparison with upper bounds obtained in previous work. The advantages of the functional proposed for applications to realistic systems is briefly discussed.Comment: 10 pages, no figure

Mean-Field vs Monte-Carlo equation of state for the expansion of a Fermi superfluid in the BCS-BEC crossover

The equation of state (EOS) of a Fermi superfluid is investigated in the BCS-BEC crossover at zero temperature. We discuss the EOS based on Monte-Carlo (MC) data and asymptotic expansions and the EOS derived from the extended BCS (EBCS) mean-field theory. Then we introduce a time-dependent density functional, based on the bulk EOS and Landau's superfluid hydrodynamics with a von Weizs\"acker-type correction, to study the free expansion of the Fermi superfluid. We calculate the aspect ratio and the released energy of the expanding Fermi cloud showing that MC EOS and EBCS EOS are both compatible with the available experimental data of $^6$Li atoms. We find that the released energy satisfies an approximate analytical formula that is quite accurate in the BEC regime. For an anisotropic droplet, our numerical simulations show an initially faster reversal of anisotropy in the BCS regime, later suppressed by the BEC fluid.Comment: 13 pages, 3 figures, presented to the 15th International Laser Physics Workshop (Lausanne, July 24-28, 2006); to be published in Laser Physic

Two-particle photoemission from strongly correlated systems: A dynamical-mean field approach

We study theoretically the simultaneous, photo-induced two-particle excitations of strongly correlated systems on the basis of the Hubbard model. Under certain conditions specified in this work, the corre- sponding transition probability is related to the two-particle spectral function which we calculate using three different methods: the dynamical-mean field theory combined with quantum Monte Carlo (DMFT- QMC) technique, the first order perturbation theory and the ladder approximations. The results are analyzed and compared for systems at the verge of the metal-insulator transitions. The dependencies on the electronic correlation strength and on doping are explored. In addition, the account for the orbital degeneracy allows an insight into the influence of interband correlations on the two particle excitations. A suitable experimental realization is discussed.Comment: 25 pp, 10 figs. to be published in PR