半空间无限深势阱中一维玻色凝聚体的反射和干涉演化

通过量子力学中的传播子方法,研究了一维情况下玻色-爱因斯坦凝聚体在半空间无限深势阱中的演化,观察到了凝聚体反射现象和自干涉图样.由于初始位置、宽度和速度的不同,凝聚体在阱壁上反射而后干涉形成不同的干涉图样,这可以用物质波的波动性给予很好的描述.同时对于凝聚体在阱壁上的碰撞问题用物质波的粒子性给予很好的解释.     

非对称的玻色-爱因斯坦凝聚中的约瑟夫森结的动力学性质

利用半经典量子理论，研究了玻色-爱因斯坦凝聚体处于非对称的约瑟夫森结的动力学行为.结果表明双势阱中不同势阱的基态能量差与其相互作用能量的比率χ=0时，凝聚体表现为约瑟夫森效应；当χ≠0时，凝聚体中既存在量子宏观隧穿效应，又存在量子宏观局域效应. 关键词： 玻色爱因斯坦凝聚 约瑟夫森结 动力学性质     

一维光晶格中玻色凝聚气体的干涉

对捕限在三维轴对称谐振势阱叠加一维光晶格的组合势中的玻色凝聚气体，文章基于平均场G-P方程并运用传播子方法，求解玻色凝聚气体基态波函数及其随时间的演化，给出了物质波干涉图样的空间分布与光晶格势周期结构之间的关系.研究表明，运用这一方法得到的光晶格势中物质波干涉条纹与光学中的多光束干涉相类似，并且与Andrews 和Peil等人的实验结果一致.物质波干涉图样随时间的演化也与Sadhan K. Adhikari通过直接数值求解G-P方程所得结果基本相同. 关键词： 玻色凝聚气体 子凝聚原子云 光晶格势 干涉     

自旋-轨道耦合二分量玻色-爱因斯坦凝聚系统的孤子解

在旋量玻色-爱因斯坦凝聚体中,孤子态作为宏观量子效应的典型状态,可以通过自旋-轨道耦合进行调控,这使得对自旋-轨道耦合玻色-爱因斯坦凝聚体中孤子的研究成为近年来超冷原子领域研究的重要课题之一.本文研究了描述一维自旋-轨道耦合二分量玻色-爱因斯坦凝聚体Gross-Pitaevskii方程的精确求解,利用直接假设及可积约化方法,给出了系统多种类型的孤子解,讨论了相应的孤子动力学以及自旋-轨道耦合效应对系统的量子磁化和自旋-极化态的影响.     

旋量玻色-爱因斯坦凝聚体拓扑性质的研究进展

实现玻色-爱因斯坦凝聚的原子大多具备内部自旋自由度,在光势阱下原子内部自旋被解冻,从而使原子可以凝聚到各个超精细量子态上,形成旋量玻色-爱因斯坦凝聚体.灵活的自旋自由度成为体系相关的动力学变量,可以使体系出现新奇的拓扑量子态,如自旋畴壁、涡旋、磁单极子、斯格明子等.本文综述了旋量玻色-爱因斯坦凝聚的实验和理论研究,旋量玻色-爱因斯坦凝聚体中拓扑缺陷的种类,以及两分量、三分量玻色-爱因斯坦凝聚体中拓扑缺陷的研究进展.     

F-P腔内自旋轨道耦合玻色-爱因斯坦凝聚体的色散研究

计算分析了处于单模Fabry-Pérot腔内的无相互作用玻色-爱因斯坦凝聚体在引入自旋轨道耦合作用下的色散关系. F-P腔为冷原子系统提供了量子化的光晶格,利用紧束缚近似和平均场近似进行二次量子化,选取合适的腔参数得到单原子缀饰态能级的具体表达式.两束弱的Raman激光和外加磁场作用于玻色-爱因斯坦凝聚体,实现了有效的自旋轨道耦合,提供了一个人工规范势,使玻色-爱因斯坦凝聚体中产生了沿腔轴方向一维的高度可控的狄拉克点.     

光晶格中超冷原子系统的磁激发

囚禁在光学晶格中的旋量凝聚体由于其长的相干性和可调控性,使其成为时下热点的多比特量子计算的潜在候选载体,清楚地了解该体系的自旋和磁性的产生和调控就显得尤为重要.本文主要从理论上回顾了光晶格原子自旋链的磁性的由来和操控手段.从激光冷却原子出发,制备旋量玻色-爱因斯坦凝聚体,并装载进光晶格,最后实现原子自旋链,对整个过程的理论研究进行了综述;就如何产生和操控自旋激发进行了详细探讨,其中包括磁孤子的制备;讨论了如何将原子自旋链应用于量子模拟.对光学晶格中的磁激发研究将会对其在冷原子物理、凝聚态物理、量子信息等各方向的应用起指导性作用.     

三势阱中玻色-爱因斯坦凝聚体的三模量子纠缠

在对称三势阱中，通过绝热地调节势阱间两个相邻势垒的高度，使得相邻的玻色-爱因斯坦凝聚体发生交叉弹性碰撞，选择适当的相互作用时间，我们提出了一种制备三体玻色-爱因斯坦凝聚场模量子纠缠的理论方案。接着，基于两体concurrence的计算方法，我们获得了该三体场模纠缠态的剩余纠缠度。[编者按]     

三势阱玻色爱因斯坦凝聚体三体复合效应的数值研究

文章中着重研究在三势阱中的凝聚体所受到的非弹性碰撞相互作用,考虑有三体复合耗散和原子填充时三势阱中玻色-爱因斯坦凝聚体动力学性质,研究了三势阱中玻色-爱因斯坦凝聚体系的自囚禁与宏观量子遂穿问题,用数值分析和解析推导的方法,发现自俘获和宏观量子隧穿现,另外,在自俘获和宏观量子隧穿进程中发现了量子拍现象,并对这些现象给出合理的解释。     

三体相互作用下三势阱中玻色-爱因斯坦凝聚体的稳定性研究

着重研究受到非弹性碰撞相互作用,即考虑有三体复合耗散和原子填充时三势阱中玻色-爱因斯坦凝聚体的动力学性质.运用三模近似,得到三个耦合的GP方程,用数值的方法得到不同散射长度的数值结果,展示了玻色-爱因斯坦凝聚体在零相位和π相位时,会出现自俘获及量子隧穿现象,且定态解的稳定性与相位有关.     

Quantum reflection of a Bose-Einstein condensate with a dark soliton from a step potential

We study dynamical behaviors of a Bose-Einstein condensate (BEC) containing a dark soliton reflected from potential wells and potential barriers, respectively. The orientation angle of the dark soliton and the width of the potential change play key roles on the reflection probability R_s. Variation of the reflection probability with respect to the orientation angle θ of the dark soliton can be well described by a cosine function R_s~cos[λ(θ-π/2)], where λ is a parameter determined by the width of the potential change. There are two characteristic lengths which determine the reflection properties. The dependence of the reflection probability on the width of the potential change shows distinct characters for potential wells and potential barriers. The length of the dark soliton determines the sensitive width of potential wells, whereas for potential barriers, the decay length of the matter wave in the region of the barrier qualifies the sensitive width of the barrier. The time evolution of the density profiles of the system during the reflection process is studied to disclose the different behaviors of matter waves in the region of the potential variation.     

Cover Picture: Fortschritte der Physik 8 / 2009

The cover page of 2009 shows high‐resolution interference “quantum carpet” patterns for the momentum wave function of an interacting Bose‐Einstein condensate (BEC). As time progresses (from back to front), the many‐body mean field interaction of the BEC first leads to a broadening of the wave function, but then also to a time‐varying interference structure by inducing site‐dependent nonlinear phase shifts when the BEC is confined in a spatially periodic potential. Imaging the wave function in momentum space for different times leads to a pattern that one reminds of a carefully woven carpet and is hence termed “quantum carpet”. Quantum carpets beautifully demonstrate the surprisingly high matter wave coherence of particle‐particle interactions in the zero‐temperature limit.     

Quantum coherent oscillations between two coupled bose-einstein condensates

The theoretical investigation of quantum coherent atomic oscillations between two coupled Bose-Einstein condensates(BECs) is studied. We apply the inseparable wave function of time-space to describe two trapped BECs in a double-well magnetic trap. According to Thomas-Fermi approximation, dynamical equations of the interwell phase difference and population imbalance are obtained. Using numerical method, coherent atomic tunneling and macroscopic quantum self-trapping(MQST) effect are investigated.     

两耦合玻色-爱因斯坦凝聚体间的量子相干振荡

理论上考察了两耦合玻色-爱因斯坦凝聚体间的相干原子振荡,我们用时空不能完全分离的波函数去描述囚禁在双磁阱中的玻色-爱因斯坦凝聚体,根据托马斯-费米近似,得到两凝聚体的相位差和布局数随时间的演化方程,应用数值计算的方法,考察了相干原子遂穿和宏观量子自囚禁效应.这些研究结果和采用双模时空分离波函数近似法得到的结果进行了比较.     

Quantum dynamics of an impurity-doped Bose-Einstein condensate system

We study the quantum dynamics of an impurity-doped Bose–Einstein condensate (BEC) system. We show how to generate the macroscopic quantum superposition states (MQSSs) of the BEC by the use of projective measurements on impurity atoms. It is found that the nonclassicality of MQSSs can be manipulated by changing the number of the impurities and their interaction with the BEC. It is shown that the BEC matter-wave field exhibits a collapse and revival phenomenon which reveals the quantum nature of the BEC matter-wave field. We investigate the micro-macro entanglement between the impurities and the BEC, and find enhancement of the micro-macro entanglement induced by the initial quantum coherence of the impurity atoms.     

Quantum Entanglement of Many Distant Bose-Einstein Condensates in an Optical Lattice by Interference

We propose a scheme to generate maximally entangled states of two distant Bose-Einstein condensates, which are trapped in different potential wells of a one-dimensional optical lattice. We show how such maximally entangled state can be used to test the Bell inequality and realize quantum teleportation of a Bose-Einstein condensate state. The scheme proposed here is based on the interference of Bose-Einstein condensates leaking out from different potential wells of optical lattice. It is briefly pointed out that this scheme can be extended to generate maximally entangled Greenberger-Horne-Zeilinger (GHZ) states of 2m (m >1) distant Bose-Einstein condensates.     

Bose-Einstein condensates in optical lattices: Spontaneous emission in the presence of photonic band gaps

An extended Bose-Einstein condensate (BEC) in an optical lattice provides a kind of periodic dielectric and causes band gaps to occur in the spectrum of light propagating through it. We examine the question whether these band gaps can modify the spontaneous emission rate of atoms excited from the BEC, and whether they can lead to a self-stabilization of the BEC against spontaneous emission. We find that self-stabilization is not possible for BECs with a density in the order of 10¹⁴ cm^-3. However, the corresponding non-Markovian behavior produces significant effects in the decay of excited atoms even for a homogeneous BEC interacting with a weak laser beam. These effects are caused by the occurrence of an avoided crossing in the photon (or rather polariton) spectrum. We also predict a new channel for spontaneous decay which arises from an interference between periodically excited atoms and periodic photon modes. This new channel should also occur in ordinary periodic dielectrics. Received 27 March 2000     

Localization of two-component Bose-Einstein condensates in optical lattices

We study nonlinear localization of a two-component Bose-Einstein condensate (BEC) in a one-dimensional optical lattice. Our theory shows that spin-dependent optical lattices can be used to effectively manipulate the nonlinear interactions between the BEC components, and to observe composite localized states of a BEC in both bands and gaps of the matter-wave spectrum.     

光晶格中玻色-爱因斯坦凝聚体的自旋和磁研究

近年应用光晶格（optical lattice)控制原子玻色－爱因斯坦凝聚体（BEC）的研究取得了突破性的进展。德国Munich研究小组首次在三维光晶格中观察到了超冷原子从BEC超流状态向Mott insulator状态的量子相变。这样的量子相变现象不仅具有重大的理论研究价值，而且为BEC的实际应用提供了新的途径。文章介绍了作者近来在光晶格中BEC的自旋和磁特性方面的一些研究进展，并探讨了它们在磁传感器及量子计算中的可能应用。