Mathematical Models and Methods in Applied Sciences
High-order compact splitting spectral methods for the rotating spin-1 Bose–Einstein condensates in a magnetic field
Xin Liu, Xiangyu Meng, Qinglin Tang, Yong Zhang
Abstract
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.