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arXiv:cond-mat/0210177 · Journal of Physics B Atomic Molecular and Optical Physics

Bose–Einstein condensation dynamics in three dimensions by the pseudospectral and finite-difference methods

Paulsamy Muruganandam, Sadhan K Adhikari

Published Jun 5, 2003• 123 citations
arXivHTMLPDF

Abstract

We suggest a pseudospectral method for solving the three-dimensional time-dependent Gross–Pitaevskii (GP) equation, and use it to study the resonance dynamics of a trapped Bose–Einstein condensate induced by a periodic variation in the atomic scattering length. When the frequency of oscillation of the scattering length is an even multiple of one of the trapping frequencies along the x , y or z direction, the corresponding size of the condensate executes resonant oscillation. Using the concept of the differentiation matrix, the partial-differential GP equation is reduced to a set of coupled ordinary differential equations, which is solved by a fourth-order adaptive step-size control Runge–Kutta method. The pseudospectral method is contrasted with the finite-difference method for the same problem, where the time evolution is performed by the Crank–Nicholson algorithm. The latter method is illustrated to be more suitable for a three-dimensional standing-wave optical-lattice trapping potential.

DOI
10.1088/0953-4075/36/12/310

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We study certain stationary and time-evolution problems of trapped Bose-Einstein condensates of weakly interacting alkali atoms described by a nonlinear Gross-Pitaevskii (GP) equation. We suggest a pseudospectral method involving Laguerre polynomials to solve the time dependent GP for a spherically symmetric trap potential. The radial wavefunction and energy values have been calculated for different nonlinearities. Further, we study the effect of suddenly changing the interatomic scattering length or harmonic oscillator trap potential in the condensate. We also investigate the frequency of oscillation due to the variation in the strength of nonlinearity.
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Using the Feshbach resonance (FR) one can change a scattering length of two-body interactions and thus affect nonlinear dynamics of excitations in a Bose-Einstein condensate. The phenomenon is described by the Gross-Pitaevskii (GP) equation with varying nonlinearity. In this work we discuss the effect of variation of the nonlinearity on excitations in a BEC placed in an optical lattice. More specifically, we describe reductions of a three-dimensional (3D) GP equation to a 1D perturbed nonlinear Schrödinger (NLS) equation for different relations among parameters; discuss periodic solutions of the NLS equation; carry out numerical study of the dynamics of the NLS equation with a periodic and parabolic trap potentials. Special attention is paid to the process of generation of trains of bright and dark matter solitons from initially periodic waves.
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Using the explicit numerical solution of the axially symmetric Gross–Pitaevskii equation, we study the oscillation of the Bose–Einstein condensate (BEC) induced by a periodic variation in the atomic scattering length a. When the frequency of oscillation of a is an even multiple of the radial or axial trap frequency, respectively, the radial or axial oscillation of the condensate exhibits resonance with a novel feature. In this nonlinear problem without damping, at resonance in the steady state the amplitude of oscillation passes through a maximum and minimum. Such a growth and decay cycle of the amplitude may keep on repeating. Similar behaviour is also observed in a rotating BEC. 1.