Peter Schmelcher

Matter-wave solitons of collisionally inhomogeneous condensates

We investigate the dynamics of matter-wave solitons in the presence of a spatially varying atomic scattering length and nonlinearity. The dynamics of bright and dark solitary waves is studied using the corresponding Gross-Pitaevskii equation. The numerical results are shown to be in very good agreement with the predictions of the effective equations of motion derived by adiabatic perturbation theory. The spatially dependent nonlinearity is found to lead to a gravitational potential, as well as to a renormalization of the parabolic potential coefficient. This feature allows one to influence the motion of fundamental as well as higher-order solitons.

Few-boson dynamics in double wells: from single-atom to correlated pair tunneling.

We investigate few-boson tunneling in a one-dimensional double well, covering the full crossover from weak interactions to the fermionization limit of strong correlations. Based on exact quantum-dynamical calculations, it is found that the tunneling dynamics of two atoms evolves from Rabi oscillations to correlated pair tunneling as we increase the interaction strength. Near the fermionization limit, fragmented-pair tunneling is observed and analyzed in terms of the population imbalance and two-body correlations. For more atoms, the tunneling dynamics near fermionization is shown to be sensitive to both atom number and initial configuration.

Confinement-induced resonances in low-dimensional quantum systems

We report on the observation of confinement-induced resonances in strongly interacting quantum-gas systems with tunable interactions for one- and two-dimensional geometry. Atom-atom scattering is substantially modified when the s-wave scattering length approaches the length scale associated with the tight transversal confinement, leading to characteristic loss and heating signatures. Upon introducing an anisotropy for the transversal confinement we observe a splitting of the confinement-induced resonance. With increasing anisotropy additional resonances appear. In the limit of a two-dimensional system we find that one resonance persists.

The helium atom in a strong magnetic field

We investigate the electronic structure of the helium atom in a magnetic field between B = 0 and . The atom is treated as a nonrelativistic system with two interacting electrons and a fixed nucleus. Scaling laws are provided connecting the fixed-nucleus Hamiltonian to the one for the case of finite nuclear mass. Respecting the symmetries of the electronic Hamiltonian in the presence of a magnetic field, we represent this Hamiltonian as a matrix with respect to a two-particle basis composed of one-particle states of a Gaussian basis set. The corresponding generalized eigenvalue problem is solved numerically, providing results for vanishing magnetic quantum number M = 0 and even or odd z-parity, each for both singlet and triplet spin symmetry. Total electronic energies of the ground state and the first few excitations in each subspace as well as their one-electron ionization energies are presented as a function of the magnetic field, and their behaviour is discussed. Energy values for electromagnetic transitions within the M = 0 subspace are shown, and a complete table of wavelengths at all the detected stationary points with respect to their field dependence is given, thereby providing a basis for a comparison with observed absorption spectra of magnetic white dwarfs.

Guiding-center dynamics of vortex dipoles in Bose-Einstein condensates

A quantized vortex dipole is the simplest vortex molecule, comprising two countercirculating vortex lines in a superfluid. Although vortex dipoles are endemic in two-dimensional superfluids, the precise details of their dynamics have remained largely unexplored. We present here several striking observations of vortex dipoles in dilute-gas Bose-Einstein condensates, and develop a vortex-particle model that generates vortex line trajectories that are in good agreement with the experimental data. Interestingly, these diverse trajectories exhibit essentially identical quasiperiodic behavior, in which the vortex lines undergo stable epicyclic orbits.

Atoms and molecules in strong external fields

White Dwarfs for Physicists D. Koester. Magnetic White Dwarfs Observations in Cosmic Laboratories S. Jordan. Hydrogen in Strong Electric and Magnetic Fields and Its Application to Magnetic White Dwarfs S. Friedrich, et al. Helium Data for Strong Magnetic Fields Obtained by Finite Element Calculations M. Braum, et al.. The Spectrum of Atomic Hydrogen in Magnetic and Electric Fields of White Dwarf Stars P. Fassbinder, W. Schweizer. Neutron Star Atmospheres G. Pavlov. Hydrogen Atoms in Neutron Star Atmospheres: Analytical Approximations for Binding Energies A.Y. Potekhin. Absorption of Normal Modes in a Strongly Magnetized Hydrogen Gas T. Bulik, G. Pavlov. Electronic Structure of Light Elements in Strong Magnetic Fields P. Pouree, et al. From Field-Free Atoms to Finite Molecular Chains in Very Strong Magnetic Fields M.R. Godefroid. The National High Magnetic Field Laboratory - a Precis J.E. Crow. Self-Adaptive Finite Element Techniques for Stable Bound Matter-Antimatter Systems in Crossed Electric and Magnetic Fields J. Ackermann. A Computational Method for Quantum Dynamics of a Three-Dimensional Atom in Strong Fields V.S. Melezhik. 25 Additional Articles. Index.

Theory and examples of the inverse Frobenius-Perron problem for complete chaotic maps

The general solution of the inverse Frobenius-Perron problem considering the construction of a fully chaotic dynamical system with given invariant density is obtained for the class of one-dimensional unimodal complete chaotic maps. Some interesting connections between this general solution and the special approach via conjugation transformations are illuminated. The developed method is applied to obtain a class of maps having as invariant density the two-parametric beta-probability density function. Varying the parameters of the density a rich variety of dynamics is observed. Observables like autocorrelation functions, power spectra, and Liapunov exponents are calculated for representatives of this family of maps and some theoretical predictions concerning the decay of correlations are tested. (c) 1999 American Institute of Physics.

Non-zero angular momentum states of the helium atom in a strong magnetic field

The electronic structure of the helium atom in the magnetic field regime B = 0-100 au is investigated, using a full configuration-interaction approach which is based on a nonlinearly optimized anisotropic Gaussian basis set of one-particle functions. The corresponding generalized eigenvalue problem is solved for the magnetic quantum number M = -1 and for both even and odd z -parity as well as singlet and triplet spin symmetry. Accurate total electronic energies of the ground state and the first four excitations in each subspace as well as their one-electron ionization energies are presented as a function of the magnetic field. Additionally we present energies for electromagnetic transitions within the M = -1 subspace and between the M = -1 subspace and the M = 0 subspace treated in a previous work. A complete table of wavelengths and field strengths for the detected stationary points is given.

HYDROGEN MOLECULE IN A MAGNETIC FIELD : THE LOWEST STATES OF THE PI MANIFOLD AND THE GLOBAL GROUND STATE OF THE PARALLEL CONFIGURATION

The electronic structure of the hydrogen molecule in a magnetic field is investigated for parallel internuclear and magnetic field axes. The lowest states of the

Dynamics of vortex dipoles in confined Bose–Einstein condensates

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