Effect of Hund coupling in the one-dimensional SU(4) Hubbard model

The one-dimensional SU(4) Hubbard model perturbed by Hund coupling is studied, away from half-filling, by means of renormalization group and bosonization methods. A spectral gap is always present in the spin-orbital sector irrespective of the magnitude of the Coulomb repulsion. We further distinguish between two qualitatively different regimes. At small Hund coupling, we find that the symmetry of the system is dynamically enlarged to SU(4) at low energy with the result of {\it coherent} spin-orbital excitations. When the charge sector is not gapped, a superconducting instability is shown to exist. At large Hund coupling, the symmetry is no longer enlarged to SU(4) and the excitations in the spin sector become {\it incoherent}. Furthermore, the superconductivity can be suppressed in favor of the conventional charge density wave state.Comment: 10 pages, 1 figur

On the Relationship Between First Occupation and Current Occupational Status

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68361/2/10.1177_073088847400100402.pd

Hydrodynamic flow of expanding Bose-Einstein condensates

We study expansion of quasi-one-dimensional Bose-Einstein condensate (BEC) after switching off the confining harmonic potential. Exact solution of dynamical equations is obtained in framework of the hydrodynamic approximation and it is compared with the direct numerical simulation of the full problem showing excellent agreement at realistic values of physical parameters. We analyze the maximum of the current density and estimate the velocity of expansion. The results of the 1D analysis provides also qualitative understanding of some properties of BEC expansion observed in experiments.Comment: 5 pages, 3 figures, RevTeX4. To appear in Physical Review

Comorbidity and risk of infection among patients with hip fracture: a Danish population-based cohort study

Summary: Impact of comorbidity on infection risk among hip fracture patients is unclear. We found high incidence of infection. Comorbidity was an important risk factor for infection up to 1 year after surgery. Results indicates a need for additional investment in pre- and postoperative programs that assist patients with high comorbidity. Purpose: Comorbidity level and incidence of infection have increased among older patients with hip fracture. The impact of comorbidity on infection risk is unclear. We conducted a cohort study examining the absolute and relative risks of infection in relation to comorbidity level among hip fracture patients. Methods: Utilizing Danish population-based medical registries, we identified 92,600 patients aged >= 65 years undergoing hip fracture surgery between 2004 and 2018. Comorbidity was categorized by Charlson comorbidity index scores (CCI): none (CCI = 0), moderate (CCI = 1-2), or severe (CCI >= 3). Primary outcome was any hospital-treated infection. Secondary outcomes were hospital-treated pneumonia, urinary tract infection, sepsis, reoperation due to surgical-site infection (SSI), and a composite of any hospital- or community-treated infection. We calculated cumulative incidence and hazard ratios (aHRs) adjusted for age, sex, and surgery year, including 95% confidence intervals (CIs). Results: Prevalence of moderate and severe comorbidity was 40% and 19%, respectively. Incidence of any hospital-treated infection increased with comorbidity level within 0-30 days (none 13% vs. severe 20%) and 0-365 days (none 22% vs. 37% severe). Patients with moderate and severe comorbidity, compared to no comorbidity, had aHRs of 1.3 (CI: 1.3-1.4) and 1.6 (CI: 1.5-1.7) within 0-30 days, and 1.4 (CI: 1.4-1.5) and 1.9 (CI: 1.9-2.0) within 0-365, respectively. Highest incidence was observed for any hospital- or community-treated infection (severe 72%) within 0-365 days. Highest aHR was observed for sepsis within 0-365 days (severe vs. none: 2.7 (CI: 2.4-2.9)). Conclusion: Comorbidity is an important risk factor for infection up to 1 year after hip fracture surgery.Orthopaedics, Trauma Surgery and Rehabilitatio

On the 3-particle scattering continuum in quasi one dimensional integer spin Heisenberg magnets

We analyse the three-particle scattering continuum in quasi one dimensional integer spin Heisenberg antiferromagnets within a low-energy effective field theory framework. We exactly determine the zero temperature dynamical structure factor in the O(3) nonlinear sigma model and in Tsvelik's Majorana fermion theory. We study the effects of interchain coupling in a Random Phase Approximation. We discuss the application of our results to recent neutron-scattering experiments on the Haldane-gap material ${\rm CsNiCl_3}$.Comment: 8 pages of revtex, 5 figures, small changes, to appear in PR

Quantum logic between atoms inside a high Q optical cavity

We propose a protocol for conditional quantum logic between two 4-state atoms inside a high Q optical cavity. The process detailed in this paper utilizes a direct 4-photon 2-atom resonant process and has the added advantage of commonly addressing the two atoms when they are inside the high Q optical cavity.Comment: 8 pages, 3 figs. submitte

Entangled quantum tunneling of two-component Bose-Einstein condensates

We examine the quantum tunneling process in Bose condensates of two interacting species trapped in a double well configuration. We discover the condition under which particles of different species can tunnel as pairs through the potential barrier between two wells in opposition directions. This novel form of tunneling is due to the interspecies interaction that eliminates the self- trapping effect. The correlated motion of tunneling atoms leads to the generation of quantum entanglement between two macroscopically coherent systems.Comment: 4 pages, 3 figure

Nonlinear atom optics and bright gap soliton generation in finite optical lattices

We theoretically investigate the transmission dynamics of coherent matter wave pulses across finite optical lattices in both the linear and the nonlinear regimes. The shape and the intensity of the transmitted pulse are found to strongly depend on the parameters of the incident pulse, in particular its velocity and density: a clear physical picture for the main features observed in the numerical simulations is given in terms of the atomic band dispersion in the periodic potential of the optical lattice. Signatures of nonlinear effects due the atom-atom interaction are discussed in detail, such as atom optical limiting and atom optical bistability. For positive scattering lengths, matter waves propagating close to the top of the valence band are shown to be subject to modulational instability. A new scheme for the experimental generation of narrow bright gap solitons from a wide Bose-Einstein condensate is proposed: the modulational instability is seeded in a controlled way starting from the strongly modulated density profile of a standing matter wave and the solitonic nature of the generated pulses is checked from their shape and their collisional properties

Haldane-Gapped Spin Chains as Luttinger Liquids: Correlation Functions at Finite Field

We study the behavior of Heisenberg, antiferromagnetic, integer-spin chains in the presence of a magnetic field exceeding the attendant spin gap. For temperatures much smaller than the gap, the spin chains exhibit Luttinger liquid behavior. We compute exactly both the corresponding Luttinger parameter and the Fermi velocity as a function of magnetic field. This enables the computation of a number of correlators from which we derive the spin conductance, the expected form of the dynamic structure factor relevant to inelastic neutron scattering experiments, and NMR relaxation rates. We also comment upon the robustness of the magnetically induced gapless phase both to finite temperature and finite couplings between neighbouring chains.Comment: 32 pages, 8 figures; published version includes additions discussing the robustness of the magnetically induced gapless phase to ordering between chains as well as the relationship between the spin-1 chains and spin-1/2 ladders in the presence of a magnetic fiel