绝热近似下的原子光电离

将 Landau 绝热近似理论,用于处理强光场中原子光电离过程,得到了原子光电离几率的解析表达式.将这一表达式同著名的 Keldysh 公式比较,在特定的条件下,它可约化为 Keldysh 公式;同模型理论比较,它又是模型理论的近似结果.还讨论了绝热近似结果的2个可能的改进途径.     

旋波近似下光场与原子电四极矩的相互作用对原子基态的修正

光场与原子的相互作用是量子光学研究的最主要问题之一,处理光场和物质的相互作用可以在不同的理论框架中进行.本文依照半经典理论对该问题进行研究,考虑了一个金属碱原子与振荡光场的谐振耦合在旋波近似下的结果,研究并对比了不同原子序数的碱金属原子的电偶极项和电四极项与光场相互作用对原子基态的影响.     

人工规范场中冷原子气体的薛定谔方程的格点规范差分算法

对于空间不均匀的人工规范场,由于位置和动量耦合在一起,冷原子物理中常用的时间分裂谱方法将不再适用。为了计算空间不均匀的人工规范场中的冷原子动力学行为,这里给出人工规范场中冷原子气体的薛定谔方程的差分算法,在我们的算法中人工规范场使得动能项的差分出现和人工规范场的联结函数,在文中分别就阿贝场和非阿贝场用待定系数法和格点规范理论给出了处在人工规范场中的冷原子气体的薛定谔方程的格点规范差分格式。我们先以最简单的U(1)的虚拟阿贝规范场为例,用两种方法分别给出相同的差分形式。对于更为复杂的SU(N),我们以SU(2)为例用两种方法给出了差分形式。然后用所得到的差分格式计算了冷原子物理中一个很典型的现象自旋霍尔效应。     

2个二能级原子与最小热环境作用系统中的量子特性

利用全量子理论研究了2个二能级原子与单模热场相互作用的简单模型(其中一个原子是孤立的,另一个原子与单模热场相耦合,该热场为一个小微外环境),通过对该模型进行精确求解,探究小微外环境对2个相互作用二能级原子系统量子特性的影响.通过研究量子纠缠和相干特性的时间演化,讨论了相关耦合常数及环境有效温度对有关物理量演化的影响.结果表明：这一系统中,可观察到2原子间量子纠缠的突然死亡和再生的现象,分别对应弱耦合及强耦合情况,当平均光子数不同时,相干性及原子的线性熵随时间变化呈现不同的演化规律.     

Rabi模型的分析与计算

Rabi模型是量子光学的基础模型之一,它描述了一个二能级原子系统与腔内光场的相互作用.但尽管Rabi模型在物理学中有重要地位,它并不能被精确解析求解.通常的办法是将Rabi模型在旋波近似下转化为JC模型,则可以解析求解,然而JC模型只能描述量子光腔的强耦合作用,不能描述超强耦合作用.在这个工作中,为了求解Rabi模型,我们采用Phy.Rev.A,2012,86(1):2271一文中的方法对其哈密顿量进行U=exp[λσx(a++a)]的幺正变换,忽略a+和a的高阶项,将其投影在σz的本征态上,其中σz|±z〉=±|±z〉,得到一个类JC模型,再对所得哈密顿量进行分析,可以得出能量谱和波函数.在MATLAB中进行数值模拟,将数值模拟的结果与解析结果进行对比,我们发现在低能级区物理图像吻合良好.     

幺正时间演化算符的推导及其在量子信息中应用

采用J-C模型,在原子与场共振相互作用时,就半经典和全量子化两种情形下推导出量子光学中一个十分有用的幺正时间演化算符,并应用这一算符展示了一种量子隐形态传输的方案.     

原子与耦合腔相互作用系统中光场的量子特性

研究了耦合腔A和B中各囚禁一个二能级原子的情况,给出了总激发数为2时系统态矢的演化。采用数值计算方法研究了腔场的反聚束效应和亚泊松分布等量子特性的演化规律。讨论了原子的选择性测量和腔场间的耦合强度变化对腔场量子特性的影响。研究结果表明:腔场的反聚束效应和亚泊松分布随腔场间耦合系数变化存在非线性关系。另一方面,采用选择原子测量方法可增强腔场A的亚泊松分布的性质。     

一维对隧穿Bose-Hubbard模型相图分析

考虑了近邻格点相互作用后,Bose-Hubbard模型(BHM)变为拓展的Bose-Hubbard模型(EBHM)。在该模型中,有一个新的项:原子对隧穿项,它就是文章研究的重点。文章利用密度矩阵重整化群(DMRG)的方法处理EBHM,给出零温下的一维相图,并着重研究了对隧穿项对相图的影响。根据Luttinger液体理论及关联函数随格点间距的衰退,得到Berezinskii-Kosterlitz-Thouless相变临界点。     

利用腔QED实现量子态的转移

利用多个相同的两能级原子在一个强经典场驱动下同时和一个单模腔场发生相互作用模型,给出了如何实现一个量子比特的原子态的远距离转移、原子纠缠态转移的方案.该方案中的腔场处于虚激发状态,原子和腔场之间没有能量交换.因此所提出的态转移方案不受腔场热光子和腔衰减的影响,对腔的Q值要求大大降低,使实验实现成为可能.     

硝基芳烃对呆鲦鱼急性毒性的CoMFA研究

用比较分子力场分析（CoMFA）方法研究硝基苯类化合物结构与呆鲦鱼的急性毒性的关系,考察了网格结构和探针原子对构效关系的影响。建立了它们的三维定量构效关系模型（用带一个单位正电荷的K原子为探针,并固定步长为0．2nm）,发现影响生物毒性的立体场、静电场的贡献分别为0．480、0．520,该模型交叉验证的相关系数平方q^2为0．452,非交叉验证的相关系数平方R^2为0．951。在CoMFA基础上引入疏水参数lgKow,以带一个单位负电荷的Cl原子为探针,其立体场、静电场、疏水场的贡献分别为0．317,0．307,0．376。所得模型的q^2=0．866,R^2=0．994,并用该模型预测了标题化合物的急性毒性。     

在相干态表象中Jaynes－Cummings模型的简便处理

在相干态表象中，我们介绍一种简便的方法来处理Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ（ＪＣ）模型，可以将纯粹的量子问题转变为求解一些微分方程。本文的结果表明：这种方法不仅能够处理在旋转波近似下的二能级体系，也可以用来精确求解无旋转波近似时的ＪＣ模型。     

旋转中子及螺旋光纤的几何相

计算得到自旋1/2粒子在旋转磁场下的Bloch方程的严格解及精确波函数,Berry几何相可对演化波函数取绝热极限得到,并将结果与Bitter等的慢中子实验做了比较. 对旋转磁场的一般非绝热循环解,给出了Aharonov-Anandan(AA)几何相和动力学相的解析结果,并用AA几何相理论圆满的解释了有争议的螺旋光纤实验,这项研究证明的关于AA的另一定理表明:对非绝热动力学相取绝热根限时,可得到绝热的动力学相和绝热的几何相. 建议用正交态方法排除绝热近似而获得平行传输条件,从而实现所谓几何量子计算.     

旋转磁场下自旋-1粒子的精确解

利用旋转坐标系方法求得自旋 1粒子在旋转磁场下的精确解 ,用所求出的精确解计算出自旋极化矢量、三能级的Rabi振荡、非绝热动力学相和几何相等重要物理量的解析形式及数值解 .所得结果对讨论量子光学和量子计算的某些问题有一定意义 .     

Electromagnetically induced transparency with resonant nuclei in a cavity

The manipulation of light-matter interactions by quantum control of atomic levels has had a profound impact on optical sciences. Such manipulation has many applications, including nonlinear optics at the few-photon level, slow light, lasing without inversion and optical quantum information processing. The critical underlying technique is electromagnetically induced transparency, in which quantum interference between transitions in multilevel atoms renders an opaque medium transparent near an atomic resonance. With the advent of high-brilliance, accelerator-driven light sources such as storage rings or X-ray lasers, it has become attractive to extend the techniques of optical quantum control to the X-ray regime. Here we demonstrate electromagnetically induced transparency in the regime of hard X-rays, using the 14.4-kiloelectronvolt nuclear resonance of the M?ssbauer isotope iron-57 (a two-level system). We exploit cooperative emission from ensembles of the nuclei, which are embedded in a low-finesse cavity and excited by synchrotron radiation. The spatial modulation of the photonic density of states in a cavity mode leads to the coexistence of superradiant and subradiant states of nuclei, respectively located at an antinode and a node of the cavity field. This scheme causes the nuclei to behave as effective three-level systems, with two degenerate levels in the excited state (one of which can be considered metastable). The radiative coupling of the nuclear ensembles by the cavity field establishes the atomic coherence necessary for the cancellation of resonant absorption. Because this technique does not require atomic systems with a metastable level, electromagnetically induced transparency and its applications can be transferred to the regime of nuclear resonances, establishing the field of nuclear quantum optics.     

偏振奇偶相干态中光场的偏振特性

利用量子光学中表示量子化光场偏振特性的Stokes算符,讨论了偏振奇偶相干态的偏振特性,研究了在此光场中Stokes参量的涨落及其压缩特性和光场的偏振度.结果表明,在适当的参量与较小的光强下,光场的Stokes参量将出现压缩.随着光强增强,压缩减弱.由于光场的量子化,偏振度永远小于1,且与光强有关.即在量子光学中,不存在完全偏振光,只有在很强的光下,才接近于完全偏振光.     

对某一类非线性Jaynes－Cummings模型的简便处理

在相干态表象中,使用一种简便的方法处理某一类非线性Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ（ＪＣ）模型,将问题简化为求解一些常微分方程．本文的结果与前人的结果一致,但是方法比较简单．     

Strong coupling of a single photon to a superconducting qubit using circuit quantum electrodynamics

The interaction of matter and light is one of the fundamental processes occurring in nature, and its most elementary form is realized when a single atom interacts with a single photon. Reaching this regime has been a major focus of research in atomic physics and quantum optics for several decades and has generated the field of cavity quantum electrodynamics. Here we perform an experiment in which a superconducting two-level system, playing the role of an artificial atom, is coupled to an on-chip cavity consisting of a superconducting transmission line resonator. We show that the strong coupling regime can be attained in a solid-state system, and we experimentally observe the coherent interaction of a superconducting two-level system with a single microwave photon. The concept of circuit quantum electrodynamics opens many new possibilities for studying the strong interaction of light and matter. This system can also be exploited for quantum information processing and quantum communication and may lead to new approaches for single photon generation and detection.     

Nonlinear and quantum atom optics

Coherent matter waves in the form of Bose-Einstein condensates have led to the development of nonlinear and quantum atom optics - the de Broglie wave analogues of nonlinear and quantum optics with light. In nonlinear atom optics, four-wave mixing of matter waves and mixing of combinations of light and matter waves have been observed; such progress culminated in the demonstration of phase-coherent matter-wave amplification. Solitons represent another active area in nonlinear atom optics: these non-dispersing propagating modes of the equation that governs Bose-Einstein condensates have been created experimentally, and observed subsequently to break up into vortices. Quantum atom optics is concerned with the statistical properties and correlations of matter-wave fields. A first step in this area is the measurement of reduced number fluctuations in a Bose-Einstein condensate partitioned into a series of optical potential wells.     

Optical nano-imaging of gate-tunable graphene plasmons

The ability to manipulate optical fields and the energy flow of light is central to modern information and communication technologies, as well as quantum information processing schemes. However, because photons do not possess charge, a way of controlling them efficiently by electrical means has so far proved elusive. A promising way to achieve electric control of light could be through plasmon polaritons—coupled excitations of photons and charge carriers—in graphene. In this two-dimensional sheet of carbon atoms, it is expected that plasmon polaritons and their associated optical fields can readily be tuned electrically by varying the graphene carrier density. Although evidence of optical graphene plasmon resonances has recently been obtained spectroscopically, no experiments so far have directly resolved propagating plasmons in real space. Here we launch and detect propagating optical plasmons in tapered graphene nanostructures using near-field scattering microscopy with infrared excitation light. We provide real-space images of plasmon fields, and find that the extracted plasmon wavelength is very short—more than 40 times smaller than the wavelength of illumination. We exploit this strong optical field confinement to turn a graphene nanostructure into a tunable resonant plasmonic cavity with extremely small mode volume. The cavity resonance is controlled in situ by gating the graphene, and in particular, complete switching on and off of the plasmon modes is demonstrated, thus paving the way towards graphene-based optical transistors. This successful alliance between nanoelectronics and nano-optics enables the development of active subwavelength-scale optics and a plethora of nano-optoelectronic devices and functionalities, such as tunable metamaterials, nanoscale optical processing, and strongly enhanced light–matter interactions for quantum devices and biosensing applications.     

重空穴轻空穴共同作用下GaN柱形量子点的Franz-Keldysh振荡

利用包络函数和有效质量理论计算了GaN柱形量子点的电调制反射谱, 并用Airy函数表示其柱坐标下薛定谔方程的解. 着重分析了重空穴轻空穴共同作用下的GaN柱形量子点电调制反射谱的Franz-Keldysh振荡, 并比较了与重空穴、轻空穴单独作用下波形的不同. 随着调制电压逐渐增大, 重空穴轻空穴共同作用下的电调制反射谱与其单独作用时一样出现Stark频移, 即量子限制Stark频移.