Mean-field model for Josephson oscillation in a Bose-Einstein condensate on an one-dimensional optical trap

Using the axially-symmetric time-dependent Gross-Pitaevskii equation we study the phase coherence in a repulsive Bose-Einstein condensate (BEC) trapped by a harmonic and an one-dimensional optical lattice potential to describe the experiment by Cataliotti {\it et al.} on atomic Josephson oscillation [Science {\bf 293}, 843 (2001)]. The phase coherence is maintained after the BEC is set into oscillation by a small displacement of the magnetic trap along the optical lattice. The phase coherence in the presence of oscillating neutral current across an array of Josephson junctions manifests in an interference pattern formed upon free expansion of the BEC. The numerical response of the system to a large displacement of the magnetic trap is a classical transition from a coherent superfluid to an insulator regime and a subsequent destruction of the interference pattern in agreement with the more recent experiment by Cataliotti {\it et al.} [e-print cond-mat/0207139].Comment: 6 Latex pages, 6 PS and EPS figures, Accepted in European Physical Journal

Free expansion of attractive and repulsive Bose-Einstein condensed vortex states

Free expansion of attractive and repulsive Bose-Einstein condensed vortex states formed in an axially symmetric trap is investigated using the numerical solution of the time-dependent Gross-Pitaevskii equation. In a repulsive condensate the vortex-core radius is much smaller than the radial root-mean-square (rms) radius, which makes the experimental observation of the vortex core difficult. The opposite is found to be true in an attractive condensate which makes it a better candidate for experimental observation. Also, in all cases the ratio of vortex-core radius to radial rms radius increases as the angular momentum of the vortex increases. This makes the vortex states with higher angular momenta more suitable for experimental confirmation.Comment: 5 revtex pages, 7 postscript figure

Study of a degenerate dipolar Fermi gas of 161Dy atoms

We study properties of a single-component (spin polarized) degenerate dipolar Fermi gas of 161Dy atoms using a hydrodynamic description. Under axially-symmetric trapping we suggest reduced one- (1D) and two-dimensional (2D) description of the same for cigar and disk shapes, respectively. In addition to a complete numerical solution of the hydrodynamic model we also consider a variational approximation of the same. For a trapped system under appropriate conditions, the variational approximation as well as the reduced 1D and 2D models are found to yield results for shape, size and chemical potential of the system in agreement with the full numerical solution of the three-dimensional (3D) model. For the uniform system we consider anisotropic sound propagation in 3D. An analytical result for anisotropic sound propagation in uniform dipolar degenerate Fermi gas is found to be in agreement with results of numerical simulation in 3D

Collapse of attractive Bose-Einstein condensed vortex states in a cylindrical trap

Quantized vortex states of weakly interacting Bose-Einstein condensate of atoms with attractive interatomic interaction in an axially symmetric harmonic oscillator trap are investigated using the numerical solution of the time-dependent Gross-Pitaevskii (GP) equation obtained by the semi-implicit Crank-Nicholson method. Collapse of the condensate is studied in the presence of deformed traps with a larger frequency along the radial as well as along the axial directions. The critical number of atoms for collapse is calculated as a function of vortex quantum $L$. The critical number increases with angular momentum $L$ of the vortex state but tends to saturate for large $L$.Comment: 8 Latex pages, 5 postscript figures, Accepted in Phys. Rev.

Mean-field model of interaction between bright vortex solitons in Bose-Einstein condensates

Using the explicit numerical solution of the axially-symmetric Gross-Pitaevskii equation we study the dynamics of interaction among vortex solitons in a rotating matter-wave bright soliton train in a radially trapped and axially free Bose-Einstein condensate to understand certain features of the experiment by Strecker et al.[2002 Nature 417 150]. In a soliton train, solitons of opposite phase (phase delta = pi) repel and stay apart without changing shape; solitons with delta = 0 attract, interact and coalesce, but eventually come out; solitons with a general delta usually repel but interact inelastically by exchanging matter. We study and suggest future experiments with vortex solitons.Comment: 12 Revtex4 pages with 17 PS figures, Disscussion improved, References added, Evolution of three-dimensional wave function of interacting solitons plotte

Bound states of attractive Bose-Einstein condensates in shallow traps in two and three dimensions

Using variational and numerical solutions of the mean-field Gross-Pitaevskii equation for attractive interaction (with cubic or Kerr nonlinearity) we show that a stable bound state can appear in a Bose-Einstein condensate (BEC) in a localized exponentially-screened radially-symmetric harmonic potential well in two and three dimensions. We also consider an axially-symmetric configuration with zero axial trap and a exponentially-screened radial trap so that the resulting bound state can freely move along the axial direction like a soliton. The binding of the present states in shallow wells is mostly due to the nonlinear interaction with the trap playing a minor role. Hence these BEC states are more suitable to study the effect of the nonlinear force on the dynamics. We illustrate the highly nonlinear nature of breathing oscillation of these states. Such bound states could be created in BECs and studied in the laboratory with present knowhow.Comment: 16 pages, 13 ps figures, Journal of Physics

Josephson oscillation and induced collapse in an attractive Bose-Einstein condensate

Using the axially-symmetric time-dependent Gross-Pitaevskii equation we study the Josephson oscillation of an attractive Bose-Einstein condensate (BEC) in a one-dimensional periodic optical-lattice potential. We find that the Josephson frequency is virtually independent of the number of atoms in the BEC and of the inter-atomic interaction (attractive or repulsive). We study the dependence of Josephson frequency on the laser wave length and the strength of the optical-lattice potential. For a fixed laser wave length (795 nm), the Josephson frequency decreases with increasing strength as found in the experiment of Cataliotti {\it et al.} [Science {\bf 293}, 843 (2001)]. For a fixed strength, the Josephson frequency remains essentially unchanged for a reasonable variation of laser wave length around 800 nm. However, for a fixed strength, the Josephson oscillation is disrupted with the increase of laser wave length beyond 2000 nm leading to a collapse of a sufficiently attractive BEC. These features of Josephson oscillation can be tested experimentally with present set ups.Comment: 7 pages, 12 ps and eps figures, Physical Review

Bright vortex solitons in Bose Condensates

We suggest the possibility of observing and studying bright vortex solitons in attractive Bose-Einstein condensates in three dimensions with a radial trap. Such systems lie on the verge of critical stability and we discuss the conditions of their stability. We study the interaction between two such solitons. Unlike the text-book solitons in one dimension, the interaction between two radially trapped and axially free three-dimensional solitons is inelastic in nature and involves exchange of particles and deformation in shape. The interaction remains repulsive for all phase delta between them except for delta \approx 0.Comment: Version accepted in Few-Body System