微原子波导口的量子反射

随着冷原子物理研究的不断深入发展,一个新的应用方向--集成原子光学研究正在兴起.在集成原子光学中,微波导的设计是其关键.理论上,要求微原子波导不仅能相干传输物质波,而且也能相干输出物质波.近来我们对玻色-爱因斯坦凝聚体(BEC)在微波导中的传输进行了详细的研究,发现BEC通过微原子波导口输出时出现了非常有趣的量子反射现象.这种量子反射与BEC波包的形状以及微波导口的性质有关.通过详细的数值模拟及理论分析,我们发现微波导口对原子孤子波包的量子反射效应最小.通过求解BEC的非线性G-P方程,以及结合对微波导口的物理模型的构造,我们已从物理本质上对微波导口处相干物质波的量子反射有了深入的理解.在此基础上,我们建议引入新的物理机制来克服微波导口的量子反射.这一研究结果对集成原子光学及微原子波导的设计有实际指导意义.     

超冷单原子分子阵列

用光镊形成光阱囚禁单个原子、用激光将单个原子冷却到基态形成超冷原子、将超冷原子相干合成单个超冷分子、将单原子分子重排串成丰富多样的超冷单原子分子阵列,这就构成了精密相干可控的多粒子量子系统,为多种前沿科学研究与技术发展提供难得的量子平台.文章介绍近年来在单原子量子态高保真操控、异核原子量子纠缠、原子一分子耦合态相干控制...     

超冷原子系综的非高斯纠缠态与精密测量

量子精密测量是基于量子力学的基本原理对特定物理量实施测量,并利用量子效应提高测量精度的交叉科学.随着超冷原子实验技术的发展,超冷原子为量子精密测量提供了一个优异的研究平台.利用发展成熟的量子调控技术,人们可以基于超冷原子系综制备一些新奇的非高斯多粒子纠缠态.基于多体量子干涉,利用这些非高斯纠缠态作为输入,可以实现超越标准量子极限的高精度测量.本文简要综述这一研究领域的进展.     

K-Li冷碰撞散射特性的理论研究

本文应用量子方法和半经典方法计算了表征锂(6Li,7Li)原子和钾(39K,40K,41K)原子间超冷碰撞特性的散射参数,如s波散射长度,有效力程,p波散射长度等.超冷温度下6Li-39K单重态和三重态原子间的弹性散射截面主要为s波贡献,随着碰撞能量的增加散射截面有丰富的形状共振出现,计算发现单重态和三重态散射截面均存在显著的i波形状共振.此外,本文应用简并内态近似获得了超精细态相互作用时的s波散射长度.     

K-Li冷碰撞散射特性的理论研究

本文应用量子方法和半经典方法计算了表征锂(6Li,7Li) 原子和钾(39K,40K,41K) 原子间超冷碰撞特性的散射参数,如s波散射长度,有效力程,p波散射长度等。超冷温度下6Li-39K单重态和三重态原子间的弹性散射截面主要为s波贡献,随着碰撞能量的增加散射截面有丰富的形状共振出现,计算发现单重态和三重态散射截面均存在显著的i波形状共振. 此外,本文应用简并内态近似获得了超精细态相互作用时的s波散射长度.     

原子冷却技术的发展

新的物理现象的发现往往得益于新实验技术的发明,制冷技术的进步推动了包括凝聚态物理学和原子物理学等现代科学多个领域的重要发现,并促进了超导强磁铁、冷冻电镜等需要极低温度条件的新技术的发展.近年来,随着激光冷却技术的发明和不断发展,人们得以在极端低温下开展统计力学和量子力学相关的实验研究,迄今,人们已经实现了玻色-爱因斯坦凝聚态这种新奇的物态,并掌握了在单原子尺度开展量子调控研究的能力.同时,由于描述量子多体系统的希尔伯特空间的维度随系统粒子数呈指数增长,即便使用经典超级计算机处理此类问题也仍面临巨大困难,这使得基于超冷原子、离子、超导等体系的量子模拟研究成为热点.人们通过前所未有的调控能力制造人工量子系统,再直接调控并观测其量子相变过程,这为研究强关联量子系统提供了一条崭新的途径.在获得极限低温的道路上,基于热力学定律的传统制冷技术能够达到的温度极限在mK量级,但激光冷却技术却另辟蹊径,巧妙地运用光与原子的相互作用,将原子的温度降低到nK量级,这大大推动了基于超冷原子的量子模拟研究的发展.尽管激光冷却技术获得的超冷原子的温度是传统制冷技术远不能及的,但由于中性原子间相互作用强度很弱,转换成温度一般在nK级别,这意味着要观测超冷原子强关联体系中的量子多体行为,就需要进一步降低原子体系温度以减小热涨落带来的影响,这也是当前超冷原子量子模拟研究中最关键的问题之一.在本文中,我们对原子冷却技术的发展进行了回顾,总结了20世纪70年代至今超冷原子技术的突破性进展,并从调控体系的熵的角度分析并展望了超冷原子低温技术未来发展方向.     

原子质心运动的量子效应对光场量子噪声压缩的影响

考虑JaynesCummings模型中与光场相互作用的原子为超冷原子,讨论了原子质心运动的量子效应对光场两正交分量量子噪声压缩的影响,结果表明,在JaynesCummings模型中,原子质心运动的量子效应增加光场两正交分量的量子噪声,使其压缩效应消失 关键词： 超冷原子 质心运动的量子效应 光场量子噪声压缩     

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.     

超冷温度下钾和铯原子间弹性散射特性的精确计算

本文分别用量子方法和半经典方法计算了超冷钾和铯原子之间弹性碰撞的s波散射长度,有效力程和p波散射长度等散射参数. 超冷温度下³⁹K-¹³³Cs原子间的弹性散射截面主要为s波贡献,随着碰撞能量的增加散射截面有丰富的形状共振出现, 计算发现单重态和三重态截面分别存在显著的g波和d波形状共振.另外,本文应用简并内态近似方法获得了⁴¹K-¹³³Cs 超精细态相互作用时的s波散射长度.     

超冷极性分子

目前对超冷原子的研究已经从最初的原子分子物理扩展到了物理的很多分支.极性分子可以将电偶极相互作用引入到超冷体系,同时分子又与原子类似,可以灵活地被光和其他电磁场操控,因而很多理论工作都预言了超冷极性分子在超冷化学、量子模拟和量子信息等领域会有重要的应用.但由于超冷基态分子的制备非常困难,如何把超冷物理从原子发展到分子还是一个方兴未艾的课题.过去的10年间,各种分子冷却技术都取得了很大突破,本文回顾了这些进展,并着重介绍了基于异核冷原子的磁缔合结合受激拉曼转移这一技术,该技术在制备高密度的基态碱金属超冷极性分子上取得了较大的成功.本文也总结了超冷极性碱金属分子基本碰撞特性研究的一些实验结果.     

The analytical transfer matrix method for quantum reflection

In this paper, the analytical transfer matrix method (ATMM) is applied to study the properties of quantum reflection in three systems: a sech$^{2}$ barrier, a ramp potential and an inverse harmonic oscillator. Our results agree with those obtained by Landau and Lifshitz [Landau L D and Lifshitz E M 1977 \wx{Quantum Mechanics (Non-relativistic Theory)}{} (New York: Pergamon)], which proves that ATMM is a simple and effective method for quantum reflection.     

Quantum Affine Reflection Algebras of Type $$d_n^{\left( 1 \right)}$$ and Reflection Matrices

Quantum affine reflection algebras are coideal subalgebras of quantum affine algebras that lead to trigonometric reflection matrices (solutions of the boundary Yang–Baxter equation). In this paper we use the quantum affine reflection algebras of type to determine new n-parameter families of nondiagonal reflection matrices. These matrices describe the reflection of vector solitons off the boundary in affine Toda field theory. They can also be used to construct new integrable vertex models and quantum spin chains with open boundary conditions.     

Quantum reflection as the reflection of subwaves

This paper studies quantum reflection with recent research on reflection coefficient. Based on the analytical transfer matrix method, a novel explanation for this phenomenon is proposed that quantum reflection is the reflection of subwaves, which originate inherently from the inhomogeneity of the fields and is always neglected in the semiclassical regime. Comparison with exact formula and the numerical calculations for different potentials has confirmed the reliability and the validity of the proposed theory.     

Photon counts modulation in optical time domain reflectometry

The quantum fluctuation of photon counting limits the field application of optical time domain reflection. A method of photon counts modulation optics time domain reflection with single photon detection at 1.55 μm is presented. The influence of quantum fluctuation can be effectively controlled by demodulation technology since quantum fluctuation shows a uniform distribution in the frequency domain. Combined with the changing of the integration time of the lock-in amplifier, the signal to noise ratio is significantly enhanced. Accordingly the signal to noise improvement ratio reaches 31.7 dB compared with the direct photon counting measurement.     

Nonlocal Andreev reflection and spin current in a three-terminal Aharonov--Bohm interferometer

This paper theoretically reports the nonlocal Andreev reflection and spin current in a normal metal-ferromagnetic metal-superconducting Aharonov--Bohm interferometer. It is found that the electronic current and spin current are sensitive to systematic parameters, such as the gate voltage of quantum dots and the external magnetic flux. The electronic current in the normal metal lead results from two competing processes: quasiparticle transmission and nonlocal Andreev reflection. The appearance of zero spin-up electronic current (or spin-down electronic current) signals the existence of nonlocal Andreev reflection, and the presence of zero electronic current results in the appearance of pure spin current.     

Quantum conditional probability in one-dimensional scattering

A result of Wan and McLean on the asymptotic separation of states in quantum mechanics is used to analyze the motion of a particle across a one-dimensional potential of finite range in terms of quantum conditional probabilities. It is shown that probabilities conditional on transmission or reflection, defined according to the Lüders rule, yield the results to be expected by intuitive argument. The theorem of total probabilities, based on the events of transmission and reflection, is shown to hold for a class of observables, and examples are given both of observables which belong to this class and of observables which do not.     

Quantum reflection pole method for determination of quasibound states in semiconductor heterostructures

The quantum reflection pole method (QRPM) is introduced for determining quasibound state eigenenergies and their lifetimes in symmetric, asymmetric, biased, and unbiased quantum heterostructures. In the QRPM the single-band effective-mass Schrödinger equation is solved without using complex arithmetic. Calculations are much simpler to perform than with previous methods. Further, results are found to be in excellent agreement with other rigorous techniques.     

双缀饰选择反射光谱的研究

研究了薄原子蒸气中Y型四能级系统的双缀饰选择反射光谱(DSR),其线型是三条色散曲线的叠加,其中两条反常色散线型对应于双缀饰电磁感应透明(DEIT).与单光子选择反射光谱(SR）相似,DSR也具有明显的Dicke窄化现象.由于暗态超慢原子的贡献和原子跃迁的量子相干效应,从DSR光谱可观察到显著的群速变慢效应.     

Classical and Quantum Evolution of the Bianchi Type I Model

The classical and quantum evolution of an anisotropic cosmological Bianchi type I model is considered. In the classical case, the influence of the minimally coupled scalar field is taken into account. Thus the system of two equations is obtained, which are explored at the inflationary and scalaron stages. The quantum problem in view of the positive cosmological constant is considered. The principal moment of the account of an anisotropy is the occurrence of the potential barrier unbounded in zero and at infinity. Though the greatest value of the potential is less than zero and the total energy of the Universe E=0, there is an important opportunity for above-barrier reflection of the wave function of the Universe. After reflection the wave function describes the expanding Universe promptly losing anisotropy and transferring into the Friedmann Universe.     

On the Graded Quantum Yang-Baxter and Reflection Equations

We clarify the extra signs appearing in the graded quantum Yang-Baxter reflection equations, when they are written in a matrix form. We find the boundary K-matrix for the Perk-Schultz six-vertex model, thus give a general solution to the graded reflection equation associated with it.