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TURKISH JOURNAL OF PHYSICS

Effective size and expansion energy of a Bose-Einstein condensate in a 3D non-cubic optical lattice

Shemi S.M. Soliman

Published Jan 1, 2011• 1 citation
Publisher

Abstract

This work is devoted to study the temperature dependence of the effective size and expansion energy E_{x,z} of a Bose-Einstein condensate in a 3D non-cubic optical lattice. Correction due to the finite size, interatomic interaction and the deepness of the lattice potential are given simultaneously. The calculated results show that these two parameters increase with the lattice depth or the relative frequency at temperature less than the transition temperature, (T < T_o); yet it has little effect at temperatures higher than the transition temperature (T > T_o). Both the effective size and expansion energy follow a characteristic temperature dependence, i.e. , E \propto(T/T_0)^4 if T < T_0 and , E \propto (T/T_0) if T > T_0. For a 3D non cubic optical potential the effect of relative frequency is much more than the effect of the optical potential depth. Thus for a non-cubic optical potential one has to use the pure harmonically trapped boson gas as the zeroth order approximation in any perturbation or numerically treatment for this system.

DOI
10.3906/fiz-1101-86

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This work is devoted to study the temperature dependence of the effective size and expansion energy E_{x,z} of a Bose-Einstein condensate in a 3D non-cubic optical lattice. Correction due to the finite size, interatomic interaction and the deepness of the lattice potential are given simultaneously. The calculated results show that these two parameters increase with the lattice depth or the relative frequency at temperature less than the transition temperature, (T < T_o); yet it has little effect at temperatures higher than the transition temperature (T > T_o). Both the effective size and expansion energy follow a characteristic temperature dependence, i.e. , E \propto(T/T_0)^4 if T < T_0 and , E \propto (T/T_0) if T > T_0. For a 3D non cubic optical potential the effect of relative frequency is much more than the effect of the optical potential depth. Thus for a non-cubic optical potential one has to use the pure harmonically trapped boson gas as the zeroth order approximation in any perturbation or numerically treatment for this system.
In this paper we develop an analytic expression for the critical temperature for a gas of ideal bosons in a combined harmonic lattice potential, relevant to current experiments using optical lattices. We give corrections to the critical temperature arising from effective mass modifications of the low energy spectrum, finite size effects, and excited band states. We compute the critical temperature using numerical methods and compare to our analytic result. We study condensation in an optical lattice over a wide parameter regime and demonstrate that the critical temperature can be increased or reduced relative to the purely harmonic case by adjusting the harmonic trap frequency. We show that a simple numerical procedure based on a piecewise analytic density of states provides an accurate prediction for the critical temperature.
This work is devoted to study the temperature dependence of the effective width and expansion energy on the finite size and interaction effects (repulsive interactions). It is found that the effective size , and expansion energy in the radial direction E_y of a Bose gas follow a characteristic temperature dependence, i.e. , E_y \propto (T/T_0)^4 if T_0 < T and , E_y \propto (T/T_0) if T_0 > T. Our results show that these two parameters increases with the number of atoms, and with increasing repulsive interaction strength at temperature less than the transition temperature, (T < T_o); yet it has little effect at temperatures higher than the transition temperature (T > T_o). The obtained results are compared with the available experimental data for ^{87}Rb directly, full agreement is obtained.
In this paper, we suggest a conventional semiclassical approximation to calculate several thermodynamic quantities of a rotating Bose-Einstein condensation in a deep optical lattice. Expressions for the condensation fraction, critical temperature, and heat capacity are derived analytically. These expressions are obtained by considering the standard harmonic approximation of the deep optical lattice potential. The suggested approach is able to include the the finite size and the positive chemical potential effects simultaneously. The advantage of our suggested approach is in its simplicity, in comparison to the quantum-mechanical calculations (Bose-Hubbard model). Moreover, its generality allows the treatment of a finite temperature regime
We developed an approach to investigate the temperature dependence of the vortices number for the rotating superfluid Bose-Einstein condensates in a two-dimensional lattice. Our approach enabled us to parametrize the thermal average of the quantum mechanics expectation value and the vortices number in terms of the thermodynamic potential q(T)q(T)q(T) for the system under consideration. The effects of the interatomic interaction, the finite number of atoms, and optical potential depth on the vortices number are investigated. The calculated results show that the vortices number as a function of the rotation rate depends on the normalized temperature, interatomic interaction, optical potential depth, and the number of atoms in the ∈situ{\in situ}∈situ size. These results provide solid theoretical foundations for the measured experimental data for rotating condensate boson in optical lattice such as Williams et. al experiment [R. A. Williams, S. Al-Assam, and C. J. Foot, Phys. Rev. Lett. { 104} (2010) 050404.].
In this work, we investigated the thermodynamic behavior of a rotating Bose-Einstein condensation with non-zero interatomic interactions in one-dimensional optical lattice theoretically. Our system is formed by loading three dimensional boson-clouds into 1D optical lattice and subjected to rotate with angular velocity ɷ about the z axis. We employed the semiclassical Hartree-Fock approach to calculate the condensate fraction, critical temperature, entropy and the heat capacity of the system. Thereby, we investigated the effect of the rotation rate, optical potential depth and the interactions parameter on these parameters. The obtained results provide a solid theoretical foundation for the current experiments of rotating interacting Bose-Einstein condensation produced or transferred in optical lattices.
Bose–Einstein condensation in a finite one-dimensional atomic Bose gas trapped in an optical lattice is studied within Bogoliubov’s approximation and then beyond this approximation, within the static fluctuation approximation. A Bose–Hubbard model is used to construct the Hamiltonian of the system. The effect of the potential strength on the condensate fraction is explored at different temperatures; so is the effect of temperature on this fraction at different potential strengths. The role of the number of lattice points (the size effect) at constant number density (the filling factor) is examined; so is the effect of the number density on the condensate fraction. The results obtained are compared to other published results wherever possible.