部分相干的高斯谢尔模物质波的轨道角动量

部分相干物质波是处于临界温度以上的玻色冷原子气体。密度和一阶关联都满足高斯分布的部分相干物质波是高斯谢尔模(Gauss-Schell model)物质波。本文通过研究高斯谢尔模物质波一阶关联函数的相位结构,揭示出物质波在部分相干情况下的轨道角动量特点。证明扭曲相位是部分相干物质波具有的独特性质,完全相干物质波(如,玻色爱因斯坦凝聚体)不具有此相位。此外,本文举例分析了高斯谢尔模物质波在一个"柱透镜"光脉冲作用下,其轨道角动量的变化情况。     

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     

一维光晶格势中玻色凝聚气体干涉图样演化特性研究

陷俘在一维光晶格势中的玻色凝聚气体,将形成许多小的子凝聚原子云.将这些子凝聚原子云视作相干的物质波波源,求出其宏观波函数,然后对物质波干涉图样的演化特性,如粒子数密度、粒子流密度、干涉峰的运动速度以及宏观波函数的相位性质等进行研究,并讨论了当相邻子凝聚原子云间存在相对相位差时,对物质波干涉图样的影响.研究表明,物质波干涉峰是一个以一定速度运动的波包,其波长由德布如意关系式确定,波包的相位特点类似于平面波.     

半无限深势阱中自旋相关玻色-爱因斯坦凝聚体的量子反射与干涉

玻色-爱因斯坦凝聚体与势垒或势阱的量子反射及干涉是考察宏观物质波奇特物性的最有效途径之一.利用传播子方法和基于冷原子实验广泛采用的飞行时间吸收成像方案,研究自旋相关玻色-爱因斯坦凝聚体在半无限深势阱中的反射和干涉演化动力学,得到了自旋相关的凝聚体波函数的严格解析解.结果表明,当自旋相关光晶格关闭后,非局域于不同格点中相同自旋态的物质波在自由膨胀过程中发生量子干涉,形成了对比度明显的干涉条纹.与此同时,扩张的自旋相关物质波包与半无限深势阱壁相遇发生量子反射,反射波与入射波产生二重干涉,在密度分布两边对称的局部位置出现剧烈的振荡,干涉条纹表现出显著的调制效应.分析讨论了自旋态、相干输运距离和相对相位等因素对干涉条纹的影响.该研究有助于促进对自旋相关凝聚体宏观量子特性的认识,为深入检验自旋相关光晶格中凝聚体干涉的理论模型和物理机理提供依据和新方案.     

超冷~(87)Rb原子在二维光晶格中Mott绝缘态的实验实现

超冷原子气体的量子相变是研究量子关联多体物理的核心内容之一.本文采用单一激光光束通过折叠反射产生二维光晶格,通过控制激光偏振产生两种不同的二维光晶格结构,一种是两个独立的一维光晶格构成,另一种是两个方向的一维光晶格互相干涉形成.将超冷~(87)Rb原子装载到二维光晶格中,通过改变光晶格激光功率调控原子在光晶格中的隧穿强度和相互作用强度,观察到~(87)Rb原子从超流态到Mott绝缘态之间的量子相变,并且分析了两种光晶格对量子相变的影响,为今后开展光晶格中强关联物理研究奠定基础.     

玻色凝聚原子云的二次干涉及其放大效应

捕限在三维轴对称谐振势阱叠加一维光晶格势的组合势中的玻色凝聚气体，取消磁阱和光晶格势后，将形成沿轴向向两侧运动的干涉边峰.提出一个新的实验方案，使这样的干涉边峰再次相遇叠加，以探讨物质波的二次干涉效应.研究表明，在干涉边峰相干加强的区域，玻色凝聚原子云的密度会得到有效放大.基于现有的实验技术，这个新实验是可以实现的，这种效应也是可以观测得到的.     

从光晶格中释放的超冷玻色气体密度-密度关联函数研究

利用量子旋转场理论详细研究了从光晶格中释放的超冷玻色气体的空间密度-密度关联函数.由于量子旋转场理论充分考虑了光晶格中冷原子气体的粒子数涨落和相位效应,该理论能有效应用于具有强相互作用的冷原子系统,从而光晶格处于超流态到绝缘态逐渐过渡过程中的超冷原子气体的关联特性在这一理论体系下都得到了很好的描述.结果表明:随着超冷玻色气体逐渐从绝缘态向超流态过渡,其密度-密度关联图样中连续对角斜线也逐渐向分散的尖峰过渡,理论结果与目前实验观测到的结果符合.除此以外,上述密度-密度关联的结果中还包含了超冷原子系统量子耗散效应,相关结论与目前已有的理论和实验一致.     

玻色爱因斯坦凝聚体一维轴向干涉中的非线性现象

利用含时的Ｇｒｏｓｓ－Ｐｉｔａｅｖｓｋｉｉ方程,研究了轴对称的高密度玻色爱因斯坦凝聚体在干涉过程中因原子间相互人用而产生的非线性现象。发现玻色爱因斯坦凝聚体的一维轴向干涉条纹的密度分布是一种驻波状结构。通过原子波之间非线性耦合相互作用,这种结构可以表现为物质波光栅,对其周期的原子波产生衍射现象。     

二维线性与非线性光晶格中物质波孤立子的稳定性

利用变分法和数值计算方法研究了二维线性和非线性光晶格中二维玻色-爱因斯坦凝聚体系中物质波孤立子的存在及其稳定性. 利用定态变分原理及Vakhitov-Kolokolov判据总结了线性和非线性结合光晶格中几种参数组合下定态定域解的稳定性. 结果表明, 当存在二维非线性光晶格时, 在吸引和排斥相互作用的原子体系中均可以存在稳定的物质波孤立子. 另外, 利用含时变分法研究了线性和非线性光晶格中物质波孤立子随时间的传播特性, 使波包参数对时间的一阶导数等于零, 可以给出稳定状态对应的参数, 结论和定态变分法给出的结果一致. 最后用数值计算方法研究变分结果的正确性, 把变分结果作为初始条件代入Gross-Pitaevskii方程研究其随时间传播特征, 得到了稳定的传播过程, 所得到的结果和变分分析结果一致. 关键词： 线性非线性光晶格 玻色-爱因斯坦凝聚 孤立子 稳定性     

原子束多光束干涉实验的一种方法

提出了一种实现原子物质波干涉的新设想.采用一个菲涅耳波带片来压缩原子束线宽,以此照明一块刻有四缝的铜箔,观察原子束的干涉和全息现象,用来测量原子束的时间相干长度 关键词： 原子束 干涉 全息     

非球面检测中最佳入射球面波和最佳参考球面波的确定

为了能够对非球面光学元件面型进行高精度的干涉检测,提出了一种确定最佳入射球面波和最佳参考球面波的新方法。该方法通过计算分析入射球面波与非球面反射波干涉条纹密度,确定最佳入射球面波的波源位置;通过计算分析在干涉图记录平面CCD上干涉条纹的密度,确定非球面检测时参考球面波波源的最佳位置。应用该理论与方法,不仅可明确非球面检测时CCD等光路元件选型的具体策略,而且可用于指导非球面检测调试过程,并能够通过对干涉图的深入分析,获得更多被测非球面的信息。     

Optical interference and pulse propagation in multimode fibers

The role played by optical interference in determining the propagation of pulses in multimode fibers is examined under conditions of mode independence and mode coupling. Single pulses and pulse-pairs generated by a source that has arbitrary temporal and spatial coherence are considered, and the role played by the spatial integration at the detector, which effectively is a form of spatial incoherence, is investigated. It is shown that three forms of optical interference may result under different conditions of source spatiotemporal coherence—intramodal, intermodal, and interpulse interference. These effects change the profile of received pulses in a, in general, nonlinear way.     

Optical interference and pulse propagation in multimode fibers

The role played by optical interference in determining the propagation of pulses in multimode fibers is examined under conditions of mode independence and mode coupling. Single pulses and pulse-pairs generated by a source that has arbitrary temporal and spatial coherence are considered, and the role played by the spatial integration at the detector, which effectively is a form of spatial incoherence, is investigated. It is shown that three forms of optical interference may result under different conditions of source spatiotemporal coherence—intramodal, intermodal, and interpulse interference. These effects change the profile of received pulses in a, in general, nonlinear way.     

A simple and realistic triton wave function

We propose a simple triton wave function that consists of a product of three correlation operators operating on a three-body spin-isospin state. This wave function is formally similar to that used in the recent variational theories of nuclear matter, the main difference being in the long-range behavior of the correlation operators. Variational calculations are carried out with the Reid potential, using this wave function in the so-called “symmetrized product” and “independent pair” forms. The triton energy and density distributions obtained with the symmetrized product wave function agree with those obtained in Faddeev and other variational calculations using harmonic oscillator states. The proposed wave function and calculational methods can be easily generalized to treat the four-nucleon α-particle.     

Matter wave interference of dilute Bose gases in the critical regime

Ultra-cold atomic gases provide a new chance to study the universal critical behavior of phase transition. We study theoretically the matter wave interference for ultra-cold Bose gases in the critical regime. We demonstrate that the interference in the momentum distribution can be used to extract the correlation in the Bose gas. A simple relation between the interference visibility and the correlation length is found and used to interpret the pioneering experiment about the critical behavior of dilute Bose gases [Science 315 1556(2007)]. Our theory paves the way to experimentally study various types of ultra-cold atomic gases with the means of matter wave interference.     

Does gravitational radiation exist?

An attempt is made to extend the Wheeler and Feynman absorber theory of electromagnetic radiation to the case of the gravitational field (described by the Einstein linear weak-field equations) on the assumption that the source is at the center of a sphere of matter having a density equal to the average density in the universe and a radius equal to the reciprocal of the Hubble constant. It is found that near the source the field of the matter is negligible compared to that of the source, so that one can conclude that the gravitational field generated by the source is time-symmetric (one-half advanced plus one-half retarded). One can conclude that a physical system does not lose energy as gravitational radiation, although a gravitational wave detector may record signals. It appears that there are no periodic running waves in nature, and hence no gravitons. These considerations hold also in the bimetric gravitation theory.     

Partonic effects on pion interferometry at the relativistic heavy-ion collider

Using a multiphase transport model that includes both initial partonic and final hadronic interactions, we study the pion interferometry at the Relativistic Heavy-Ion Collider. We find that the two-pion correlation function is sensitive to the magnitude of the parton-scattering cross section, which controls the parton density at which the transition from the partonic to hadronic matter occurs. Also, the emission source of pions is non-Gaussian, leading to source radii that can be more than twice larger than the radius parameters extracted from a Gaussian fit to the correlation function.