Tunnelling of topological line defects in strongly coupled superfluids

The geometric theory of vortex tunnelling in superfluid liquids is developed. Geometry rules the tunnelling process in the approximation of an incompressible superfluid, which yields the identity of phase and configuration space in the vortex collective co-ordinate. To exemplify the implications of this approach to tunnelling, we solve explicitly for the two-dimensional motion of a point vortex in the presence of an ellipse, showing that the hydrodynamic collective co-ordinate description limits the constant energy paths allowed for the vortex in configuration space. We outline the experimental procedure used in helium II to observe tunnelling events, and compare the conclusions we draw to the experimental results obtained so far. Tunnelling in Fermi superfluids is discussed, where it is assumed that the low energy quasiparticle excitations localised in the vortex core govern the vortex dynamical equations. The tunnelling process can be dominated by Hall or dissipative terms, respectively be under the influence of both, with a possible realization of this last intermediate case in unconventional, high-temperature superconductors.Comment: 51 pages, 15 figures, uses Ann. Phys. (Leipzig) style file; forms part of author's dissertation, available at http://xxx.lanl.gov/abs/cond-mat/9909166v

Many-site coherence revivals in the extended Bose-Hubbard model and the Gutzwiller approximation

We investigate the collapse and revival of first-order coherence in deep optical lattices when long-range interactions are turned on, and find that the first few revival peaks are strongly attenuated already for moderate values of the nearest-neighbor interaction coupling. It is shown that the conventionally employed Gutzwiller wavefunction, with only onsite-number dependence of the variational amplitudes, leads to incorrect predictions for the collapse and revival oscillations. We provide a modified variant of the Gutzwiller ansatz, reproducing the analytically calculated time dependence of first-order coherence in the limit of zero tunneling.Comment: 8+\epsilon{} pages of RevTex4-1, 4 figures; with an appendix added, has been published in Physical Review

Quantum simulation of cosmic inflation in two-component Bose-Einstein condensates

Generalizing the one-component case, we demonstrate that the propagation of sound waves in two-component Bose-Einstein condensates can also be described in terms of effective sonic geometries under appropriate conditions. In comparison with the one-component case, the two-component setup offers more flexibility and several advantages. In view of these advantages, we propose an experiment in which the evolution of the inflaton field, and thereby the generation of density quantum fluctuations in the very early stages of our universe during inflation, can be simulated, realizing a {\em quantum simulation via analogue gravity models}.Comment: 8 pages of RevTex4, 1 figure; added explanatory material, to appear in Physical Review

Fragmented many-body ground states for scalar bosons in a single trap

We investigate whether the many-body ground states of bosons in a generalized two-mode model with localized inhomogeneous single-particle orbitals and anisotropic long-range interactions (e.g. dipole-dipole interactions), are coherent or fragmented. It is demonstrated that fragmentation can take place in a single trap for positive values of the interaction couplings, implying that the system is potentially stable. Furthermore, the degree of fragmentation is shown to be insensitive to small perturbations on the single-particle level.Comment: 4 pages of RevTex4, 3 figures; as published in Physical Review Letter

Interest rate policies and domestic savings mobilization: A survey of the empir. evidence of Asian countries

The liberalization of interest rates has become more and more an integrated part of the policy advice given to developing countries in order to stimulate domestic savings and to improve the allocative efficiency of investments . One of the most critical assumptions behind this policy approach refers to a high and positive interest rate elasticity of savings. Empirically, this assumption seems not to be supported unanimously. Giovannini (1983) , for instance, concludes from his survey of a sample of econometric studies that the notion of a positive impact of higher interest rates on national savings is not warranted empirically. This would lead to the conclusion that the expected success from interest liberalization policies would be questionable. However, such a judgement is not justified because the mentioned survey has various shortcomings. First, the range of empirical studies covered in the overview is rather limited. Second, the discussion of the interest rate elasticity of savings is not differentiated enough with respect to different savings aggregates. Third, some of the specification and methodological problems existing in estimating interest elasticities of savings are not tackled sufficiently.