环形势阱中旋转玻色爱因斯坦凝聚体的基态

应用托马斯-费米近似和虚时演化数值方法研究环形势阱中旋转玻色爱因斯坦凝聚体的基态密度分布.当增加其旋转角频率,或者增加环形势阱的宽度及相应的中心高度,凝聚体基态密度分布均从涡旋晶格相转变为巨涡旋相.当旋转角频率为零时,增加环形势阱的宽度及相应的中心高度,凝聚体基态密度分布从一个圆盘变为圆环.解析结果与数值结果相互吻合.     

谐振子势与高斯势的联合势阱中两分量旋转玻色爱因斯坦凝聚体的基态特性和自旋纹理

研究了两分量旋转玻色爱因斯坦凝聚体在谐振子势与高斯势的联合势阱中的基态特性和自旋纹理。通过托马斯-费米近似得到每组分凝聚体在相混合态时密度分布首次形成中心洞的临界旋转角频率,并根据旋转角频率与临界旋转角频率的关系,给出了两分量凝聚体的三种不同的基态密度分布:两个都是盘、一个是盘和另一个是环、两个都是环。对于相分离的情况,针对两分量粒子数严重不平衡的凝聚体分别作托马斯费米近似,解析地给出了两分量凝聚体的两种对称基态密度分布。同时研究了凝聚体在两分量的界面处形成的两种赝自旋纹理,它们分别是巨斯格明子和同轴双环斯格明子。     

谐振子势与高斯势的联合势阱中玻色-爱因斯坦凝聚体的涡旋结构

本文用虚时演化法研究了玻色-爱因斯坦凝聚体在谐振子势与高斯势的联合势阱中的涡旋结构,给出了旋转角频率和原子间相互作用强度对涡旋分布的影响,以及对凝聚体中量子化涡旋、鬼涡旋以及隐涡旋分布的不同作用。在联合势阱中凝聚体除了量子化涡旋和鬼涡旋外,在势阱中心位置还出现了隐涡旋。当相互作用强度一定时,可见涡旋数和隐涡旋数随着旋转角频率的增大而增加。当旋转角频率一定时,随着原子间相互作用逐渐增强,可见涡旋数随之增加,而隐涡旋数并没有改变。我们分析发现,只有考虑了隐涡旋之后,才能满足费曼规则。     

环形势阱中自旋-轨道耦合旋转玻色-爱因斯坦凝聚体的基态

研究了在环形势阱中自旋-轨道耦合旋转玻色-爱因斯坦凝聚体的基态结构.探索了自旋-轨道耦合作用和旋转效应对基态的影响.结果发现,在环形势阱下,基态结构呈现环形分布的half-skyrmion链.调节自旋-轨道耦合强度,不仅可以改变体系内half-skyrmion数量,而且能够调控half-skyrmion环形排列的对称性.随着旋转频率增大,体系从平面波相转化为环形对称排列的half-skyrmion链相,最后过渡到三角格子的half-skyrmion相.讨论了自旋相互作用和势阱形状对基态的影响.自旋-轨道耦合强度和旋转频率作为体系的调控参数,可用于控制不同基态相间的转化.     

三维非谐势阱中玻色-爱因斯坦凝聚的数值计算

本文从G-P平均势场理论出发,探讨了三维球对称非谐势阱中玻色-爱因斯坦凝聚(BEC)的G-P方程;用数值计算方法研究了三维球对称非谐势阱中原子间有相互作用的玻色-爱因斯坦凝聚气体的基态解;分析了非谐振势能项对玻色-爱因斯坦凝聚体的分布、能量和化学势的影响.     

三维非谐势阱中玻色－爱因斯坦凝聚的数值计算

本文从G－P平均势场理论出发,探讨了三维球对称非谐势阱中玻色－爱因斯坦凝聚(BEC)的G－P方程;用数值计算方法研究了三维球对称非谐势阱中原子间有相互作用的玻色－爱因斯坦凝聚气体的基态解;分析了非谐振势能项对玻色－爱因斯坦凝聚体的分布、能量和化学势的影响。     

六极子磁场中自旋轨道耦合玻色-爱因斯坦凝聚体的基态结构

研究囚禁在环形势中的Rashba自旋轨道耦合玻色-爱因斯坦凝聚体在六极子磁场中的基态特性。在这种情况下,磁场破坏了自旋轨道耦合哈密顿量的旋转对称性,但系统仍具有2π/3的离散对称性。数值结果发现:在弱相互作用情况下,六极子磁场和Rashba自旋轨道耦合使环形囚禁的凝聚体呈类六边形的基态密度分布,当磁场强度超过某一临界值时,凝聚体将崩塌;在强相互作用情况下,半量子涡旋出现在凝聚体中,且被六极子磁场钉在方位角Ф=nπ/3的径向位置,涡旋的旋转方向取决于径向磁场的方向。     

改进打靶法求解Gross-Pitaevskii方程及三个凝聚体的干涉

用改进的打靶法求解零温简谐势阱中中性原子玻色-爱因斯坦凝聚的一维Gross-Pitaevskii方程,给出不同非线性参数时凝聚体基态的本征值.用辛算法研究三个凝聚体在撤掉陷俘势后产生的干涉,和三个凝聚体处于同-陷俘势中的干涉及周期性演化,讨论不同的相对相位对凝聚体干涉的影响.     

有效质量法调控原子玻色-爱因斯坦凝聚体的双阱动力学

操控原子玻色-爱因斯坦凝聚体在双势阱中的动力学通常是通过改变势阱深度来实现,本文提出了一种基于调节原子有效质量的控制方案,可以在不改变双阱势的前提下操控凝聚体的双阱动力学.利用双模近似,本文解析地导出了超冷原子在双阱势中的隧穿强度和相互作用强度对有效质量的依赖关系,并基于平均场近似数值模拟了在有效质量调节下的凝聚体动力学演化,展示了隧穿振荡和自束缚等典型的双阱动力学行为.此外,本文的研究还发现,借助负有效质量效应,这一方案甚至可以等效地实现对负散射长度原子凝聚体双阱动力学行为的操控.     

玻色-爱因斯坦凝聚中的非正则涡旋态及其动力学

玻色-爱因斯坦凝聚中由于非线性相互作用引起的涡旋激发态一直是超冷原子研究的热点.然而相关研究都集中在具有整数拓扑荷的正则涡旋态.本文研究了具有幂指数、新型幂指数和振荡型三种相位分布的非正则涡旋光与凝聚体相互作用而产生的非正则涡旋态凝聚体的动力学性质.研究表明非正则涡旋具有动力学不稳定性,其密度分布显著依赖于光场相位结构参数.不同非正则涡旋衰变形成具有不同分布的正则涡旋簇,展现出丰富的动力学激发斑图.特别是新型幂指数非正则涡旋态衰变后会在凝聚体内形成稳定的正多边形正则涡旋簇结构.由于非正则涡旋光的相位结构破坏了凝聚体的旋转对称性,凝聚体的角动量不再是量子化的,且其随光场方位角幂次或振荡频率的变化与相应的非正则涡旋光场自身演化具有明显差别.在动力学演化过程中,具有新型幂指数相位的非正则涡旋态凝聚体质心保持不变,而对于具有幂指数和振荡型相位的非正则涡旋态凝聚体,两者的质心轨迹是一个中心为坐标原点的非标准椭圆.     

A Rotating Bose-Einstein Condensation in a Toroidal Trap

We have studied the ground state configurations of a rotating Bose-Einstein condensation in a toroidal trap as the radius of the central Gaussian potential expands adiabatically. Firstly, we observe that the vortices are devoured successively into the central hole of the condensate to form a giant vortex as the radius of the trap expands. When all the pre-existing vortices are absorbed, the angular momentum of the system still increase as the radius of the
gaussian potential enlarges. When increasing the interaction strength, we find that more singly quantized vortices are squeezed into the condensate, but the giant vortex does not change.     

Ground-states and rotational properties of a spin–orbit-coupled spin-1 Bose–Einstein condensate in a concentrically coupled toroidal trap

We investigate the ground states of an antiferromagnetic spin-1 Bose–Einstein condensate with spin–orbit coupling in a concentrically coupled toroidal trap. A new necklace-type state with double-ring structure is created in the system due to the spin–orbit coupling. The petal number of the necklace state is increased with enhancing the strength of the spin–orbit coupling. When the rotation is introduced, the condensate can be dragged into the outer trough of the trap by increasing the rotation frequency, which makes it possible to realize the exotic ground state combined by the necklace state at the inner trough and the persistent flow at the outer one. Once the two troughs of the toroidal trap are populated by the persistent flow at the specific effective interactions between atoms, the hidden vortices may occur in the central region of the trap and at the barrier between the two troughs. In addition, the visible vortex with the laminar structure can be generated under the more effective atomic interaction.     

Observation of persistent flow of a Bose-Einstein condensate in a toroidal trap

We have observed the persistent flow of Bose-condensed atoms in a toroidal trap. The flow persists without decay for up to 10 s, limited only by experimental factors such as drift and trap lifetime. The quantized rotation was initiated by transferring one unit variant Planck's over 2pi of the orbital angular momentum from Laguerre-Gaussian photons to each atom. Stable flow was only possible when the trap was multiply connected, and was observed with a Bose-Einstein condensate fraction as small as 20%. We also created flow with two units of angular momentum and observed its splitting into two singly charged vortices when the trap geometry was changed from multiply to simply connected.     

Effects of Higher Order Interaction on Vortex Formation in Bose-Einstein Condensates

We consider theoretically the formation of vortex in rotating Bose-Einstein condensates (BECs) with higher order interaction (HOI). Our results are obtained from the twodimensional Gross-Pitaevskii equation. As the first step, for the certain number vortices, we discuss the ground state properties and show that the critical rotation frequency for HOI is smaller than those without HOI. As the increasing of HOI strength, the critical rotation frequency decreases. In addition, we verify that the Feynman rule is meet well. Moreover, we study the vortex dynamics.Numerical results indicate that the angular momentum remains almost unchanged irrespective of the HOI strength. The time taken for the nucleation of vortices pays less for strong HOI. These results suggest that the HOI is favorable to rotate the condensate, and this mechanism is useful to control the vortex number in BECs.

     

Measurement of the angular momentum of a rotating bose-einstein condensate

We study the quadrupole oscillation of a Bose-Einstein condensate of 87Rb atoms confined in an axisymmetric magnetic trap, after it has been stirred by an auxiliary laser beam. The stirring may lead to the nucleation of one or more vortices, whose presence is revealed unambiguously by the precession of the axes of the quadrupolar mode. For a stirring frequency Omega below the single vortex nucleation threshold Omega(c), no measurable precession occurs. Just above Omega(c), the angular momentum deduced from the precession is approximately Planck's over 2pi. For stirring frequencies above Omega(c) the angular momentum is a smooth and increasing function of Omega, until an angular frequency is reached at which the vortex lattice disappears.     

Quantized rotation of atoms from photons with orbital angular momentum

We demonstrate the coherent transfer of the orbital angular momentum of a photon to an atom in quantized units of variant Planck's over 2pi, using a 2-photon stimulated Raman process with Laguerre-Gaussian beams to generate an atomic vortex state in a Bose-Einstein condensate of sodium atoms. We show that the process is coherent by creating superpositions of different vortex states, where the relative phase between the states is determined by the relative phases of the optical fields. Furthermore, we create vortices of charge 2 by transferring to each atom the orbital angular momentum of two photons.     

Thermal fluctuations of vortex matter in trapped bose-einstein condensates

We perform Monte Carlo studies of vortices in three dimensions in a cylindrical confinement, with uniform and nonuniform density. The former is relevant to rotating 4He; the latter is relevant to a rotating trapped Bose-Einstein condensate. In the former case, we find dominant angular thermal vortex fluctuations close to the cylinder wall. For the latter case, a novel effect is that at low temperatures the vortex solid close to the center of the trap crosses directly over to a tensionless vortex tangle near the edge of the trap. At higher temperatures an intermediate tensionful vortex liquid located between the vortex solid and the vortex tangle may exist.     

Bose-Einstein condensates with large number of vortices

We show that as the number of vortices in a three dimensional Bose-Einstein condensate increases, the system reaches a "quantum Hall" regime where the density profile is a Gaussian in the xy plane and an inverted parabolic profile along z. The angular momentum of the system increases as the vortex lattice shrinks. However, Coriolis force prevents the unit cell of the vortex lattice from shrinking beyond a minimum size. Although the recent MIT experiment is not exactly in the quantum Hall regime, it is close enough for the present results to be used as a guide. The quantum Hall regime can be easily reached by moderate changes of the current experimental parameters.