Yong-Kai Liu

Exact solitons and manifold mixing dynamics in the spin-orbit–coupled spinor condensates

We derive exact static as well as moving solitonic solutions to the one-dimensional spin-orbit-coupled F = 1 Bose-Einstein condensates. The static polar soliton is shown to be the ground state by the imaginary-time evolution method. It shows a helical modulation of the order parameter due to the spin-orbit coupling. In particular, the moving soliton exhibits a periodic oscillation among the particle numbers of the hyperfine states. We further explore the temporal evolution of the static polar soliton and find that the spin-polarization exhibits dynamical oscillations. This disappearance and re-emergence of the ferromagnetic state indicates the mixing of the ferromagnetic and the antiferromagnetic manifolds. Copyright (C) EPLA, 2014

Half-knot in the spinor condensates

We present an exact solution to the stationary coupled nonlinear Gross-Pitaevskii equations, which govern the motion of the spinor Bose-Einstein condensates. The solitonic solution is a twisted half-skyrmion in 3D space. By making a map from the Cartesian coordinates to the toroidal coordinates, we demonstrate it is a linked half-unknot with a fractional topological charge.

HALF-SKYRMION IN SPINOR BOSE–EINSTEIN CONDENSATES

In this paper, we present exact solutions to the F = 1 spinor Bose–Einstein condensates with only spin-independent energy by adopting a method of separating the variables, which exhibit nontrivial topology. These solutions can form solitonic fractional vortex and solitonic half-skyrmion with a Q = 1/2 topological charge in the two-dimensional system. We further address a three-dimensional prototype solution.

Stable knots in the trapped Bose-Einstein condensates

The knot of the spin-texture is studied within the two-component Bose-Einstein condensates which are described by the nonlinear Gross-Pitaevskii equations. We start from the noninteracting equations including an axisymmetric harmonic trap to obtain an exact solution, which exhibits a nontrivial topological structure. The spin-texture is a knot with an integral Hopf invariant. The stability of the knot is verified by numerically evolving the nonlinear Gross-Pitaevskii equations along imaginary time.

Three-dimensional solitons in two-component Bose—Einstein condensates

We investigate a kind of solitons in the two-component Bose-Einstein condensates with axisymmetric configurations in the R-2 x S-1 space. The corresponding topological structure is referred to as Hopfion. The spin texture differs from the conventional three-dimensional (3D) skyrmion and knot, which is characterized by two homotopy invariants. The stability of the Hopfion is verified numerically by evolving the Gross-Pitaevskii equations in imaginary time.

FRACTIONAL WINDINGS OF THE SPINOR CONDENSATES ON A RING

We study the uniform solutions to the one-dimensional (1D) spinor Bose-Einstein condensates on a ring. These states explicitly display the associated motion of the super-current and the spin rotation, which give rise to fractional winding numbers according to the various compositions of the hyperfine states. It simultaneously yields a fractional factor to the global phase due to the spin-gauge symmetry. All fractional windings can be denoted as nk/(m + n), with nk < m + n < 2F, for arbitrary spin-F Bose-Einstein condensation (BEC). Our method can be applied to explore the fractional vortices by identifying the ring as the boundary of two-dimensional (2D) spinor condensates.

Numerical simulation of micro-atmospheric environment by LES in a district of Beijing

This paper investigates wind field and traffic pollutant dispersion at street level in a local urban area. A coupling method is employed between the mesoscale model weather research and forecast (WRF) for the atmospheric flow of whole city and the large eddy simulation (LES) method for local environmental flows. A combined model is proposed for building clusters in the urban area. The wind speed, temperature and carbon monoxide concentration fields are computed from 9 am of October 26 2009 to 8 am of the next day in a district of Beijing and the results show a good agreement with the observation.