强聚焦泵浦产生纠缠光子的Hong-Ou-Mandel干涉

(86.6±1.0)Hong-Ou-Mandel (HOM)干涉是光子的一种非经典效应,在量子光学中起到重要作用.偏硼酸钡(β-barium borate, BBO)具有较高的非线性效率,常被用来产生双光子态,进而展示HOM干涉.然而,在以前的实验中,人们往往使用带通滤光片对双光子的频谱进行过滤,所得光谱由带通滤光片直接决定,而对BBO晶体自身的原始光谱,特别是泵浦光强聚焦下的原始光谱,缺乏系统性研究.本文对泵浦光强聚焦条件下BBO晶体产生的双光子纠缠态光谱分布和HOM干涉进行了深入研究.理论计算发现,使用50 mm透镜聚焦的情况和无聚焦情况相比,下转换光的光谱宽度会增加7.4倍, HOM干涉条纹的宽度会减少为无聚焦情况的1/8,干涉条纹可见度会从53.0%提高到98.7%.实验上使用II型BBO晶体制备了能量-时间纠缠态,并进行了HOM干涉,获得了%的干涉可见度.干涉可见度极大提高的原因在于强聚焦改善了光谱的对称性.此外,本文提出的不同入射角获得不同光谱分布的技术方案有望在未来应用于高维量子纠缠态的制备.     

Generation of GHZ States via Deterministic Entanglement Concentration

We present the generation of six-particle Greenberger Horne-Zeilinger （GHZ） states via deterministic entanglement concentration and generalize the scheme to the case of 2N particles. We show that arbitrary 2N-particle GHZ states can be obtained with certain probability via entanglement concentration. This may provide a new perspective for the preparation of multi-particle GHZ states. This study is also an exploration on the theory of deterministic entanglement concentration.     

利用双面腔制备n原子GHZ态

提出了一种利用双面腔制备多原子GHZ态的方法.当腔中囚禁原子处于特定态时,腔可能反射入射的单光子脉冲,也可能透射它.这个特性可以引起囚禁原子和输入腔肠的纠缠.数值模拟显示制备的多原子GHZ态具有很高的保真度和成功率.而且原子自发辐射等内禀噪声只对成功率有影响,而对保真度几乎没有影响.另外,对高Q腔和原子的L-D条件的不要求,提升了试验实现的可行性.     

利用优化理论实现量子局域纯态转化

利用优化理论实现了量子局域纯态转化,详细给出了其中用到的双随机矩阵的求解过程,求出了这个双随机矩阵的通解,构造了两种不同的正定算符值测量(POVM)算子方案来实现局域纯态转化。这样我们把优化理论在局域纯态转化中的应用做了进一步的完善和延伸,为这种理论的进一步推广和实验上的实现奠定了基础。     

基于光子轨道角动量的密码通信方案研究

设计了一个基于两个正交的光子轨道角动量态的量子密码通信方案.在该方案中,Alice使用具有独特设计的激光器,随机发送有确定轨道角动量的光子;Bob采用由两个达夫棱镜组成的光束旋转器,对光子的轨道角动量态进行测量.对系统安全性的讨论表明,Eve采用截获重发、攻击单臂等攻击手段,其窃听行为都会被发现.理论证明,该方案不需要通信双方实时监测和调整参考系,同时避免了BB84,B92协议因发送基和测量基不一致而丢弃一半信息的问题,从而提高了密钥生成效率. 关键词： 量子保密通信 轨道角动量     

General and Optimal Scheme for Local Conversion of Pure States

We present general and optimal schemes for local conversion of pure states, via one specific example. First, we give the general solution of the doubly stochastic matrix. Then, we find the general and optimal positive-operator-valued measure （POVM） to realize the local conversion of pure states. Lastly, the physical realization of the POVM is discussed. We show that our scheme has a more general and better effect than other schemes.     

Teleporting a quantum controlled-Not with one target/two targets gate using two partially entangled states

This paper considers the teleportation of quantum controlled-Not (CNOT) gate by using partially entangled states. Different from the known probability schemes, it presents a method for teleporting a CNOT gate with unit fidelity and unit probability by using two partially entangled pairs as quantum channel. The method is applicable to any two partially entangled pairs satisfying the condition that their smaller Schmidt coefficients μ and ν are (2μ + 2ν - 2μν - 1)≥0. In this scheme, the sender's local generalized measurement described by a positive operator valued measurement (POVM) lies at the heart. It constructs the required POVM. It also puts forward a scheme for teleporting a CNOT with two targets gate with unit fidelity by using same quantum channel. With assistance of local operations and classical communications, three spatially separated users are able to complete the teleportation of a CNOT with two targets gate with probability of (2μ + 2ν- 1). With a proper value of μ and ν, the probability could reach nearly 1.     

宽波长范围的多色脉冲光学自相关测量

基于Si光电二极管和GaAsP光电二极管的双光子吸收特性,设计了800～2 000 nm宽带波长测量范围的简易自相关仪实验装置.利用该装置测量了克尔透镜锁模钛宝石激光、掺镱光纤锁模激光和掺铒光纤放大脉冲激光的脉宽;通过引入额外群延迟色散和增加自相位调制效应调控脉冲的净啁啾,研究了自相关曲线变化特性.结果表明：该自相关仪实验装置能够有效测量由净啁啾改变导致的自相关曲线变化特性,能够满足不同波长脉冲激光实验教学应用场合的需求.     

用Greenberger-Horne-Zeilinger态作量子信道实现多点控制的远程单比特幺正变换

提出了一个用三粒子纠缠的GHZ态作为量子信道实现多点控制的远程单比特幺正变换的操纵方案.在该方案中,发送者Alice能“传送”一个幺正变换给远距离的接收者Bob,此幺正变换的结构分别由Alice和Bob决定.而Alice与Bob间的量子信道宽度,亦远程单比特幺正变换的成功操纵几率则由第三者Cindy控制.Cindy与Alice（Bob）间的经典通讯也由Cindy控制.     

Simple Algorithm for Deterministic Entanglement Concentration

We first present the general solution and the simplest special solution of the doubly stochastic matrix used in deterministic entanglement concentration. Then, we give a better scheme to realize deterministic entanglement concentration. Under this scheme, the concentration is realized, and more importantly, two partially entangled pairs concentrate to four-particle Greenberger-Horne-Zeilinger （GHZ） states with a certain probability.