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arXiv:1611.06358 · Journal of Physics A Mathematical and Theoretical

Analytical solutions of the coupled Gross–Pitaevskii equations for the three-species Bose–Einstein condensates

Y M Liu, Bao Cheng-guang

Published Jun 14, 2017• 4 citations
arXivHTMLPDF

Abstract

Abstract The coupled Gross–Pitaevskii equations for the ground state of the three-species condensates have been solved analytically under the Thomas–Fermi approximation. Six types of spatial configurations in the miscible phase are found. The whole parameter space has been divided into zones, each of which supports a specific configuration (miscible or immiscible). The boundaries of the zones are described by analytical formulae. Due to the division, the variation of the spatial configuration against the parameters can be visualized, and the effects of the parameters can thereby be understood. There are regions in the parameter space where the configuration is highly sensitive to the parameters. These regions are tunable and valuable for the determination of the parameters.

DOI
10.1088/1751-8121/aa7272

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Abstract The coupled Gross–Pitaevskii equations for the ground state of the three-species condensates have been solved analytically under the Thomas–Fermi approximation. Six types of spatial configurations in the miscible phase are found. The whole parameter space has been divided into zones, each of which supports a specific configuration (miscible or immiscible). The boundaries of the zones are described by analytical formulae. Due to the division, the variation of the spatial configuration against the parameters can be visualized, and the effects of the parameters can thereby be understood. There are regions in the parameter space where the configuration is highly sensitive to the parameters. These regions are tunable and valuable for the determination of the parameters.
Abstract Under the Thomas–Fermi approximation, an approach is proposed to solve the coupled Gross–Pitaevskii equations (CGP) for the two-species Bose–Einstein condensate analytically. The essence of this approach is to find out the building blocks to build the solution. By introducing the weighted strengths, relatively simpler analytical solutions have been obtained. A number of formulae have been deduced to relate the parameters when the system is experimentally tuned at various status. These formulae demonstrate the combined effect of the parameters, and are useful for the evaluation of their magnitudes. The whole parameter space is divided into zones, where each supports a specific phase. All the boundaries separating these zones have analytical expressions. Based on the division, the phase diagrams against any set of parameters can be plotted. In addition, by introducing a model for the asymmetric states, the total energies of the lowest symmetric and asymmetric states have been compared. Thereby, in which case the former will be replaced by the latter has been evaluated. The CGP can be written in a matrix form. For repulsive inter-species interaction V AB , when the parameters vary and cross over the singular point of the matrix, a specific state transition will happen and the total energy of the lowest symmetric state will increase remarkably. This provides an excellent opportunity for the lowest asymmetric state to emerge as the ground state. For attractive V AB , when the parameters tend to a singular point, the system will tend to collapse. The effects caused by the singular points have been particularly studied.
Abstract We study harmonically trapped two-species Bose–Einstein condensates within the Gross–Pitaevskii formalism. By invoking the Thomas–Fermi approximation, we derive an analytical solution for the miscible ground state in a particular region of the system’s parameter space. This solution furnishes a simple formula that relates the interspecies interaction strength to the second spatial moments of the density distribution of the minority condensate species. Accompanying numerical simulations confirm the accuracy of the solution and the interaction strength formula for sufficiently large numbers of condensed particles. The introduced formula may provide an additional scheme for determining interspecies scattering lengths that complements existing methods, such as those based on collective-excitation spectroscopy of the two-species condensates or on collisional measurements on thermal samples.
A general approach is proposed to solve the coupled Gross-Pitaevskii equations (CGP) for K-species Bose-Einstein condensates (BEC). Analytical solutions have been obtained under the Thomas-Fermi approximation. We aim at finding out the common features of the K-species BEC. In particular, two types of phase-transitions, full-state-transition and partial-state transition, are found. In the former all species are involved in the transition, while in the latter only a few specified species are essentially involved. This leads to the criticality and the hidden criticality (previously found in multi-band superconductivity). We further found that the former originates from the singularity of the whole matrix of the CGP, while the latter originates from the singularity of a specified sub-matrix (which is contributed by only a few specified species). It is emphasized that the singularity is not a by-product of the TFA, but is inherent in the CGP.
We identify all possible classes of solutions for two-component Bose-Einstein condensates (BECs) within the Thomas-Fermi (TF) approximation and check these results against numerical simulations of the coupled Gross-Pitaevskii equations (GPEs). We find that they can be divided into two general categories. The first class contains solutions with a region of overlap between the components. The other class consists of non-overlapping wavefunctions and also contains solutions that do not possess the symmetry of the trap. The chemical potential and average energy can be found for both classes within the TF approximation by solving a set of coupled algebraic equations representing the normalization conditions for each component. A ground state minimizing the energy (within both classes of states) is found for a given set of parameters characterizing the scattering length and confining potential. In the TF approximation, the ground state always shares the symmetry of the trap. However, a full numerical solution of the coupled GPEs, incorporating the kinetic energy of the BEC atoms, can sometimes select a broken-symmetry state as the ground state of the system. We also investigate effects of finite-range interactions on the structure of the ground state.
Abstract Employing a general variational method and perturbation theory, we derived explicit solutions for the description of one-dimensional two species Bose–Einstein condensates confined by a harmonic trap potential in an optical lattice. We consider the system of two coupled Gross–Pitaevskii equations (GPE) and derive explicit expressions for the chemical potentials and wavefunctions in terms of the atom–atom interaction parameters and laser intensity. We have compared our results with the numerical solutions of the GPE and performed a quantitative analysis for the both considered methods. We underline the importance of the obtained explicit solutions to characterize the density profile or degree of miscibility of the two components.
An approach is proposed to solve the coupled Gross-Pitaevskii equations (CGP) of the 3-species BEC in an analytical way under the Thomas-Fermi approximation (TFA). It was found that, when the strength of a kind of interaction increases and crosses over a critical value, a specific type of state-transition will occur and will cause a jump in the total energy. Due to the jump, the energy of the lowest symmetric state becomes considerably higher. This leaves a particular opportunity for the lowest asymmetric state to replace the symmetric states as the ground state. It was further found that the critical values are related to the singularity of either the matrix or a sub-matrix of the CGP. These critical values are not arising from the TFA but inherent in the CGP, and they can be analytically expressed. Furthermore, a model (in which two kinds of atoms separated from each other asymmetrically) has been proposed for the evaluation of the energy of the lowest asymmetric state. With this model the emergence of the asymmetric ground state is numerically confirmed under the TFA. The theoretical formalism of this paper is quite general and can be generalized for BEC with more than three species.