近日，意大利帕多瓦大学的Francesco Ancilotto与意大利米兰理工大学的Luciano Reatto合作并取得一项新进展。经过不懈努力，他们成功控制具有光学晶格的玻色-爱因斯坦凝聚体中的量子涡旋动力学和涡旋-反涡旋湮灭。相关研究成果已于2024年7月3日在国际知名学术期刊《物理评论A》上发表。

本文采用Gross-Pitaevskii理论研究了周期势影响下平面几何中温度为0 K的⁸⁷Rb玻色子。研究人员聚焦于一维(1D)和二维(2D)光学晶格中涡旋激励的静力学和动力学，以及涡旋激励强度的函数。研究人员计算了涡旋的能量如何取决于其核心的位置，以及涡旋为了在超流体中移动而必须克服的能量势垒。涡旋偶极子（即一对手性相反的涡旋）的动力学行为显著不同于均匀超流体。在一维情境下，涡旋偶极子的动力学受到平行密度脊的显著影响：若两涡旋位于同一通道内，它们将相互靠近直至迅速湮灭；若分布于不同通道，则偶极子虽经历刚性平移，但其速度受光学晶格强度调控，甚至可能相对于均匀超流体情况出现速度符号的反转，并伴随有叠加于其上的振荡运动。

当系统被限制在圆形阱中时，还观察到了沿通道平移与振荡的复合运动模式，这些振荡既可以是纵向（沿通道方向），也可以是横向的。在所有情况下，横向运动均呈现单向性，确保涡旋核心不会越过其初始位置附近的平衡态。进一步地，在考察的二维晶格结构（包括正方形、三角形和蜂窝状）中，涡旋偶极子的两个涡旋主要通过在平衡位置间的跳跃来移动，并逐渐靠近直至湮灭。这种动态行为在一定程度上与偶极玻色子超固态中涡旋偶极子的行为相似。此外，研究还发现，光学势的快速衰减显著增强了涡旋核心处密度空穴的可视性。

据悉，在光学晶格的影响下，可以在冷原子区域产生具有强空间调制的超流体。

附：英文原文

Title: Controlling quantum vortex dynamics and vortex-antivortex annihilation in Bose-Einstein condensates with optical lattices

Author: Francesco Ancilotto, Luciano Reatto

Issue&Volume: 2024/07/03

Abstract: Superfluids with strong spatial modulation can be experimentally produced in the area of cold atoms under the influence of optical lattices. Here we address  ⁸⁷ Rb   bosons at T=0 K in a flat geometry under the influence of a periodic potential with the Gross-Pitaevskii theory. The statics and dynamics of vortex excitations are studied in the case of one-dimensional (1D) and of two-dimensional (2D) optical lattices, as function of the intensity of the optical lattice. We compute how the vortex energy depends on the position of its core and the energy barrier that a vortex has to surmount in order to move in the superfluid. The dynamics of a vortex dipole, a pair of vortices of opposite chirality, differ profoundly from the case of a uniform superfluid. In the 1D case, when parallel ridges of density are present, the dynamics depends on the positions of the two vortices. If they are in the same channel between two ridges, then the two vortices approach each other until they annihilate each other in a short time. If the two vortices are in distinct channels, the dipole undergoes a rigid translation but with a velocity depending on the intensity of the optical lattice and this translation velocity can even change sign with respect to the case of the uniform superfluid. Superimposed on this translation an oscillatory motion is also present. A superposition of translation along a channel and an oscillation is also found with a single vortex when the system is bounded inside a circular trap. These oscillatory motions can be both longitudinal, i.e., along the channel, as well as transverse. In all cases the transverse motions are one sided, in the sense that the vortex core never crosses the equilibrium position nearest the starting position. In the case of the 2D lattices we study (square, triangular, and honeycomb), the two vortices of a dipole move mainly by jumps between equilibrium positions and approach each other until annihilation. This behavior has some similarity with what has been found for a vortex dipole in the supersolid state of dipolar bosons. We show that a rapid ramp down of the optical potential improves the visibility of the density holes at the vortex core.

DOI: 10.1103/PhysRevA.110.013302

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.110.013302