Institute of Modern Physics, Northwest University, Xi'an, 710069, China.
Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xi'an, 710069, China.
Sci Rep. 2016 Jul 28;6:29066. doi: 10.1038/srep29066.
Dynamics of vortex clusters is essential for understanding diverse superfluid phenomena. In this paper, we examine the dynamics of vortex quadrupoles in a trapped two-dimensional (2D) Bose-Einstein condensate. We find that the movement of these vortex-clusters fall into three distinct regimes which are fully described by the radial positions of the vortices in a 2D isotropic harmonic trap, or by the major radius (minor radius) of the elliptical equipotential lines decided by the vortex positions in a 2D anisotropic harmonic trap. In the "recombination" and "exchange" regimes the quadrupole structure maintains, while the vortices annihilate each other permanently in the "annihilation" regime. We find that the mechanism of the charge flipping in the "exchange" regime and the disappearance of the quadrupole structure in the "annihilation" regime are both through an intermediate state where two vortex dipoles connected through a soliton ring. We give the parameter ranges for these three regimes in coordinate space for a specific initial configuration and phase diagram of the vortex positions with respect to the Thomas-Fermi radius of the condensate. We show that the results are also applicable to systems with quantum fluctuations for the short-time evolution.
涡旋簇的动力学对于理解各种超流现象至关重要。在本文中，我们研究了囚禁在二维（2D）玻色-爱因斯坦凝聚体中的四极涡旋的动力学。我们发现，这些涡旋簇的运动分为三个不同的区域，这些区域可以通过在二维各向同性谐振子陷阱中涡旋的径向位置，或者通过在二维各向异性谐振子陷阱中由涡旋位置决定的等势能线的长半轴（短半轴）来完全描述。在“复合”和“交换”区域中，四极结构保持不变，而在“湮灭”区域中，涡旋会永久地相互湮灭。我们发现，“交换”区域中电荷翻转的机制和“湮灭”区域中四极结构的消失都是通过一个中间状态来实现的，在这个中间状态中，两个涡旋偶极子通过孤子环连接。我们给出了在特定初始构型和涡旋位置相对于凝聚体托马斯-费米半径的相图的坐标空间中，这三个区域的参数范围。我们表明，这些结果对于短时间演化的具有量子涨落的系统也是适用的。
