Non-perturbative theoretical description of two atoms in an optical lattice with time-dependent perturbations

A theoretical approach for a non-perturbative dynamical description of two interacting atoms in an optical lattice potential is introduced. The approach builds upon the stationary eigenstates found by a procedure described in Grishkevich et al. [Phys. Rev. A 84, 062710 (2011)]. It allows presently to treat any time-dependent external perturbation of the lattice potential up to quadratic order. Example calculations of the experimentally relevant cases of an acceleration of the lattice and the turning-on of an additional harmonic confinement are presented.Comment: 8 pages, 6 figure

A simple parameter-free one-center model potential for an effective one-electron description of molecular hydrogen

For the description of an H2 molecule an effective one-electron model potential is proposed which is fully determined by the exact ionization potential of the H2 molecule. In order to test the model potential and examine its properties it is employed to determine excitation energies, transition moments, and oscillator strengths in a range of the internuclear distances, 0.8 < R < 2.5 a.u. In addition, it is used as a description of an H2 target in calculations of the cross sections for photoionization and for partial excitation in collisions with singly-charged ions. The comparison of the results obtained with the model potential with literature data for H2 molecules yields a good agreement and encourages therefore an extended usage of the potential in various other applications or in order to consider the importance of two-electron and anisotropy effects.Comment: 8 pages, 6 figure

Theoretical description of two ultracold atoms in finite 3D optical lattices using realistic interatomic interaction potentials

A theoretical approach is described for an exact numerical treatment of a pair of ultracold atoms interacting via a central potential that are trapped in a finite three-dimensional optical lattice. The coupling of center-of-mass and relative-motion coordinates is treated using an exact diagonalization (configuration-interaction) approach. The orthorhombic symmetry of an optical lattice with three different but orthogonal lattice vectors is explicitly considered as is the Fermionic or Bosonic symmetry in the case of indistinguishable particles.Comment: 19 pages, 5 figure

Population Trends of Red-Cockaded Woodpeckers in Texas

We tracked population trends of Red-cockaded Woodpeckers (Picoides borealis) in eastern Texas from 1983 through 2004. After declining precipitously during the 1980s, woodpecker population trends on federal lands (National Forests and Grasslands in Texas, but excluding the Big Thicket National Preserve) increased between 1990 and 2000, and have been stable to slightly decreasing over the past four years. Litigation against the U.S. Forest Service in the mid 1980s reversed a severe population decline, whereas litigation during the past 8 years hampered recovery efforts for the Red-cockaded Woodpecker. Red-cockaded Woodpecker populations on private and State of Texas lands have steadily declined over he past 15 years, most likely the result of demographic isolation. Limited availability of old pines suitable for cavity excavation, inadequate fire regimes to control hardwood midstory, and demographic dysfunction resulting from woodpecker group isolation remain as significant obstacles to recovery in most populations

Frustrated collisions and unconventional pairing on a quantum superlattice

We solve the problem of scattering and binding of two spin-1/2 fermions on a one-dimensional superlattice with a period of twice the lattice spacing analytically. We find the exact bound states and the scattering states, consisting of a generalized Bethe ansatz augmented with an extra scattering product due to "asymptotic" degeneracy. If a Bloch band is doubly occupied, the extra wave can be a bound state in the continuum corresponding to a single-particle interband transition. In all other cases, it corresponds to a quasi-momentum changing, frustrated collision.Comment: 4 pages, 2 figure

Quantum Chessboards in the Deuterium Molecular Ion

We present a new algorithm for vibrational control in deuterium molecules that is feasible with current experimental technology. A pump mechanism is used to create a coherent superposition of the D2+ vibrations. A short, intense infrared control pulse is applied after a chosen delay time to create selective interferences. A `chessboard' pattern of states can be realized in which a set of even- or odd-numbered vibrational states can be selectively annihilated or enhanced. A technique is proposed for experimental realization and observation of this effect using 5 fs pulses of 790 nm radiation, with intermediate intensity (5e13 W/cm2)Comment: 12 pages, 5 figure

Photoassociative spectroscopy at long range in ultracold strontium

We report photoassociative spectroscopy of $^{88}$Sr$_2$ in a magneto-optical trap operating on the ${^1S_0}\to{^3P_1}$ intercombination line at 689 nm. Photoassociative transitions are driven with a laser red-detuned by 600-2400 MHz from the ${^1S_0}\to{^1P_1}$ atomic resonance at 461 nm. Photoassociation takes place at extremely large internuclear separation, and the photoassociative spectrum is strongly affected by relativistic retardation. A fit of the transition frequencies determines the ${^1P_1}$ atomic lifetime ($\tau=5.22 \pm 0.03$ ns) and resolves a discrepancy between experiment and recent theoretical calculations.Comment: 4 pages, 4 figures, submitte

Species Using Red-Cockaded Woodpecker Cavities in Eastern Texas

Because of its ability to excavate cavities in living pines, the Red-cockaded Woodpecker (Picoides borealis) is a keystone species in the fire-disclimax, pine ecosystems of the southeastern United States. Many species representing multiple taxonomic classes are dependent on this woodpecker species for the cavities it creates. We examined the occupants of Red-cockaded Woodpecker cavities during spring, late summer, and winter. Cavities enlarged by other species of woodpeckers and unenlarged cavities were examined in two habitat conditions: loblolly (Pinus taeda) -shortleaf (P. echinata) pine and longleaf pine (P. palustris) habitats. Red-cockaded Woodpecker cavities provided cavity habitat for seven species of birds, two species of squirrels, skinks, frogs, spiders, moths, and numerous species of Hymenoptera

Red-Cockaded Woodpecker Nestling Provisioning and Reproduction in Two Different Pine Habitats

We obtained nestling provisioning and reproductive data from 24 Red-cockaded Woodpecker (Picoides borealis) groups occupying two different pine habitats-longleaf pine (Pinus palustris) and a mixture of loblolly (P. taeda) and shortleaf pine (P. echinata)--in eastern Texas during 1990 and 1901. Habitat data were collected within 800 m of each group\u27s cavity-tree cluster. Feeding trips per nest and prey biomass per feeding trip were significantly greater in lohlolly-shortleaf pine habitat. There were few significant correlations between reproductive/provisioning and habitat variables in either pine habitat. Pines dying from infestation by southern pine beetles (Dendroctonus frontalis) were more common in loblolly-shortleaf than in longleaf pine habitat. In addition, adult male Red-cockaded Woodpeckers weighed more in loblolly-shortleaf pine habitat. Indices of southern pine beetle abundance in loblolly-shortleaf pine habitat were negatively correlated with but positively correlated with prey biomass delivered to nestlings. We number of feeding trips per nestling, hypothesize that the greater abundance of southern pine beetles and associated arthropods in loblolly-shortleaf pine habitat, ancl the resulting higher frequency of dying pines containing an abundant food source, were associated with an elevated prey biomass available to both nestling and adult Red-cockaded Woodpeckers

Red-Cockaded Woodpecker Nesting Success, Forest Structure, and Southern Flying Squirrels in Texas

For several decades general opinion has suggested that southern flying squirrels (Gluucomys volans) have a negative effect on Red-cockaded Woodpeckers (Picoides borealis) through competition for cavities and egg/nestling predation. Complete removal of hardwood trees from Red-cockaded Woodpecker cavity tree clusters has occurred on some forests because southern flying squirrel abundance was presumed to be associated with the presence and abundance of hardwood vegetation. In some locations, southern flying squirrels have been captured and either moved or killed in the name of Red-cockaded Woodpecker management. We determined southern flying squirrel occupancy of Red-cockaded Woodpecker cavities in loblolly (Pinus taeda)-shortleaf (P. echinata) pine habitat (with and without hardwood midstory vegetation) and longleaf pine (P. pulustris) habitat (nearly devoid of hardwood vegetation) during spring, late summer, and winter during 1990 and 1991. Flying squirrel use of Red-cockaded Woodpecker cavities was variable and was not related to presence or abundance of hardwood vegetation. Woodpecker nest productivity was not correlated with flying squirrel use of woodpecker cavities within clusters. In addition, we observed six instances where Red-cockaded Woodpeckers successfully nested while flying squirrels occupied other cavities in the same tree. Our results suggest that complete removal of hardwoods from woodpecker cluster areas in loblolly and shortleaf pine habitat may not provide benefits to the woodpeckers through reduction of flying squirrel numbers. Reduction of hardwood midstory around cavity trees, however, is still essential because of the woodpecker\u27s apparent innate intolerance of hardwood midstory foliage