Abstract. We propose high-order compact splitting Fourier spectral methods to compute the dynamics of dipolar Bose–Einstein condensates (BECs) with arbitrary-angle rotation. The Hamiltonian is split into a linear part that consists of the Laplace and rotation and a nonlinear part that includes all the remaining terms. For the linear subproblem, we factorize the linear operator into a product of simple suboperators using the exact classical-quantum correspondence and semigroups decomposition, and these suboperators are integrated exactly in either physical or phase space. Importantly, we first derive explicit formulas for the splitting coefficients originally obtained by numerically solving a nonlinear system. The nonlinear part is solved exactly in physical space, and the convolution-type nonlocal potential with a singular kernel is computed via the Far-field Smooth Approximation (FSA) method with spectral accuracy. This “compact” splitting, involving only two operators, significantly simplifies the design of high-order schemes. Our method achieves high-order temporal precision and spectral spatial accuracy with near-optimal efficiency, and it is explicit, easy to implement and unconditionally stable. In addition, we derive some dynamical properties and conduct a comprehensive investigation, including accuracy confirmation, property verification, interaction of quantized vortices, and dynamics under honeycomb potential.
Abstract. We propose high-order compact splitting Fourier spectral methods to compute the dynamics of dipolar Bose–Einstein condensates (BECs) with arbitrary-angle rotation. The Hamiltonian is split into a linear part that consists of the Laplace and rotation and a nonlinear part that includes all the remaining terms. For the linear subproblem, we factorize the linear operator into a product of simple suboperators using the exact classical-quantum correspondence and semigroups decomposition, and these suboperators are integrated exactly in either physical or phase space. Importantly, we first derive explicit formulas for the splitting coefficients originally obtained by numerically solving a nonlinear system. The nonlinear part is solved exactly in physical space, and the convolution-type nonlocal potential with a singular kernel is computed via the Far-field Smooth Approximation (FSA) method with spectral accuracy. This “compact” splitting, involving only two operators, significantly simplifies the design of high-order schemes. Our method achieves high-order temporal precision and spectral spatial accuracy with near-optimal efficiency, and it is explicit, easy to implement and unconditionally stable. In addition, we derive some dynamical properties and conduct a comprehensive investigation, including accuracy confirmation, property verification, interaction of quantized vortices, and dynamics under honeycomb potential.
We propose high-order compact splitting Fourier spectral methods to compute the dynamics of rotating spin-1 Bose–Einstein condensates (BECs) under an Ioffe-Pritchard magnetic field. We split the Hamiltonian into a linear part, which consists of the Laplace, rotation and Zeeman energy terms, and a nonlinear part, which includes all the remaining terms. This “compact” splitting, involving only two operators, significantly simplifies the construction of high-order schemes. For the linear subproblem, we factorize the linear operator as a product of simple sub-operators using the exact classical-quantum correspondence and semigroups decomposition, and such sub-operators are well approximated by Fourier spectral method and integrated exactly in phase space as usual. Importantly and surprisingly, the splitting coefficients, originally determined by a nonlinear equation, can actually be computed exactly by solving a linear system, ending up with explicit formulas. For the nonlinear subproblem, we derive an exact formula of the spin vector, which is not conserved in presence of the magnetic field, and transform it into a linear problem. Then we design explicit high-order schemes using Magnus integrators. Our scheme achieves spectral accuracy in space and high-order precision in time with near-optimal efficiency. It is explicit, easy to implement and unconditionally stable. In addition, we derive some properties of our numerical scheme and conduct a comprehensive investigation, including accuracy confirmation, efficiency test, property verification, interaction of quantized vortices and dynamics under honeycomb potential.
This paper investigates the dynamics of spin-2 Bose-Einstein condensates (BECs) with rotation and spin-orbit coupling (SOC). In order to better simulate the dynamics, we present an efficient high-order compact splitting Fourier spectral method. This method splits the Hamiltonian into a linear part, which consists of the Laplace, rotation and SOC terms, and a nonlinear part that includes all the remaining terms. The wave function is well approximated by the Fourier spectral method and is numerically accessed with discrete Fast Fourier transform (FFT). For linear subproblem, the handling of rotation term and SOC term poses a major challenge. Using a function mapping based on rotation, we can integrate the linear subproblem exactly and explicitly. This mapping we propose not only helps eliminate the rotation term, but also prevents the SOC term from evolving into a time-dependent form. The nonlinear subproblem is integrated analytically in physical space. Such "compact" splitting involves only two operators and facilitates the design of high-order splitting schemes. Our method is spectrally accurate in space and high order in time. It is efficient, explicit, unconditionally stable and simple to implement. In addition, we derive some dynamical properties and carry out a systematic study, including accuracy and efficiency tests, dynamical property verification, the SOC effects and dynamics of vortex lattice.
In this paper, an efficient time-splitting Fourier spectral method is proposed to simulate the dynamics of spin-orbit coupled spin-1 Bose-Einstein condensates (SOC spin-1 BECs). We split the Hamiltonian into a linear part, which consists of the Laplace and SOC terms, and a nonlinear part that includes all the remaining terms. The linear subproblem is integrated analytically in phase space by solving an ordinary differential system of constant coefficient matrix. While, for the nonlinear subproblem, it is proved the coefficient matrix is actually time-independent in physical space, therefore, the nonlinear subproblem can be integrated exactly. Based on such two-step splitting, we construct high-order schemes to simulate the dynamics. Our method is spectrally accurate in space and high order in time. It is efficient, explicit, unconditionally stable and simple to implement. In addition, we derive some dynamical properties for SOC spin-1 BECs. Extensive numerical results are presented to confirm the accuracy and efficiency, illustrate the dynamical properties at discrete level, and show interesting physics of SOC spin-1 BECs, such as the SOC effects and different wave patterns.
A time-splitting generalized-Laguerre–Fourier–Hermite pseudospectral method is proposed for computing the dynamics of rotating Bose–Einstein condensates (BECs) in two and three dimensions. The new numerical method is based on the following: (i) the use of a time-splitting technique for decoupling the nonlinearity; (ii) the adoption of polar coordinates in two dimensions and cylindrical coordinates in three dimensions such that the angular rotation term becomes constant coefficient; and (iii) the construction of eigenfunctions for the linear operator by properly scaling the generalized-Laguerre, Fourier, and Hermite functions. The new method enjoys the following properties: (i) it is explicit, time reversible, and time transverse invariant; (ii) it conserves the position density and is spectrally accurate in space and second-order or fourth-order accurate in time; and (iii) it solves the problem in the original whole space instead of in a truncated artificial computational domain. The method is also extended to solve the coupled Gross–Pitaevskii equations for the dynamics of rotating two-component and spin-1 BECs. Extensive numerical results for the dynamics of BECs are reported to demonstrate the accuracy and efficiency of the new method for rotating BECs.
We numerically study the nonlocal Gross–Pitaevskii equation (NGPE) which describes the dynamics of Bose–Einstein condensates (BEC) with dipole–dipole interaction at extremely low temperature. In preparation for the numerics, first we reformulate the dimensionless NGPE into a Schrödinger–Poisson system. Then, we discretize the three-dimensional Schrödinger–Poisson system in space by a sixth-order compact finite difference method and in time by a splitting technique. By means of three-dimensional discrete fast Sine transform, we develop a fast solver for the resulting discretized system. Finally, we present numerical examples in three dimensions to demonstrate the power of the numerical methods and to discuss some physics of dipolar BEC. The merits of the proposed method for the NGPE are that it is fast and unconditionally stable. Moreover, the method is of spectral-like accuracy in space, and conserves the particle number and the energy of the system in the discretized level.
In this article, we propose an efficient and spectrally accurate numerical method to compute the ground states of three-dimensional (3D) rotating dipolar Bose-Einstein condensates (BEC) under strongly anisotropic trapping potentials.The kernel singularity, convolution non-locality and density anisotropy together complicate the dipolar potential evaluation. The fast rotation mechanism not only induces a complicated energy landscape with many local minima, but also creates a large number of vortices in the condensates. Such factors collectively make the ground state computation challenging in terms of convergence, accuracy and efficiency, especially for 3D anisotropic systems. Coupled with Fourier spectral discretization, we proposed a preconditioned conjugate gradient method (PCG) by integrating the anisotropic truncated kernel method (ATKM) for the dipolar potential evaluation. An adaptive step size control strategy is designed and ATKM allows for a spectral accuracy without introducing any extra anisotropy-dependent memory requirement or computational time. Our algorithm is spectrally accurate, highly efficient and memory-economic. Extensive numerical results are presented to confirm the accuracy and efficiency, together with applications to study impacts of the model parameters on critical rotational frequency, energies and chemical potential. Furthermore, these simulations reveal additional novel ground state patterns, such as bent vortices.