光子反聚束效应的增强——双路双光子吸收光束之干涉

本文提出一种方案,通过双路双光子吸收后光束之相消性干涉,增强光子反聚束效应可达10~(12)倍。因此实验能观察到双光子吸收过程产生的光子反聚束现象。     

钠蒸气中基于钠原子的三种电离机制的研究

本文探寻到钠原子５Ｓ态的双光子共振三光子电离通道,进行了如下实验,在钠原子分子系统中,通过两种方激发式：双光子共振激发（图１中ａ通道所示）和混合共振激发（图１中ｂ通道所示）,将钠原子激发到５Ｓ态,再吸收一个同样频率的光子而电离。进行电离信号检测,第一种激发方式有一个电离峰,对应３Ｓ－５Ｓ双光子共振激发电离;第二种方式有两个电离峰,对应３Ｐ－５Ｓ双光子共振激发电离。这对基于钠原子５Ｓ态电离,提供了新     

分离通道光子非定域相干的半经典解释

J.D.Franson提出一项关于验证空间与时间Bell不等式的双光子相关实验,这一设想由Mandel等人利用下转换光子对的双光子相关实验进行了验证。实验中使由非线性晶体在高单色性高频激光作用下产生的一对光子,分别通过两组Mach—Zehnder类型干涉仪组成的1、2两个分离通道,每一干涉仪都包含由半透镜与反射镜组成的长光程与短光程臂,两臂之间的时间延迟远大于通过光束的相干时间,这也可认为是光程差大于光子波包的长度,两组干涉仪各自的两臂间程差基本一致,都具有前述特点。通过两分离干涉仪通     

双光子光折变介质中非相干耦合屏蔽光伏孤子对

为了获得在有外加电场的双光子光伏光折变介质中存在着稳态非相干耦合屏蔽光伏空间孤子对的结果,对外加电场的双光子光伏光折变介质中,两束偏振方向和波长都相同的互不相干光束的耦合进行了理论研究。结果表明,这种孤子对是由偏振态和波长都相同的两束互不相干光耦合而成的,它可以看成是双光子非相干屏蔽孤子对和双光子非相干光伏孤子对的统一形式,当外加电场很强可忽略光伏效应时,它类似于已报道的双光子屏蔽孤子对,而当外加电场为0时,它相当于闭路条件下的双光子光伏孤子对。这就预言了非相干耦合暗-暗和亮-亮双光子屏蔽光伏空间孤子对的存在。     

罗丹明6G的非简并双光子吸收特性研究

利用飞秒激光泵浦-探测技术,在实验上研究了常用荧光染料分子罗丹明6G的非简并双光子激发荧光特性,并测试了其非简并双光子吸收截面。与等效波长下文献报道的罗丹明6G的简并双光子吸收截面作对比,发现其非简并双光子吸收截面总是大于简并双光子吸收截面,从实验上证明了双光子吸收过程中的中间态共振增强效应。基于有效态模型,用量子化学的方法从理论上分析罗丹明6G的双光子吸收截面,将理论拟合与实验测试结果进行对比,发现理论与实验具有很好的一致性。     

双光子三能级光子回波及其在原子间碰撞截面测量中的应用

本文用弹球模型讨论了双光子三能级光子回波的形成。实验上在 Na 蒸汽中观察到了这种光子回波。并报导了用光子回波测量 Na 3 D-3 P 态原子和 Ar 原子碰撞截面的结果。     

基于虚拟仪器平台的双光子吸收测试系统仿真研究

双光子吸收材料的非线性光学性能在光限幅、3D微制造、高密度存储和双光子荧光显微镜等领域具有广泛的应用前景和潜在的实用价值。寻找具有大双光子吸收截面的材料已成为光学及其交叉学科中最诱人,最活跃的研究领域之一。目前用于双光子吸收效应测量的主要手段有Z-scan法,双光子诱导荧光法,双光子瞬态吸收光谱法等。由于Z-scan法具有光路简单、灵敏度高及可同时测量三阶非线性极化率实部及虚部等诸多优点,已在相关领域获得了大量应用。目前有关该技术的研究基本集中在实验测试方面,理论仿真相对较少。利用虚拟仪器平台对应用于双光子吸收测试的Z-scan实验进行了仿真研究,讨论了实验参数合理性选择及实验参数间的依赖规律。通过仿真分析,重点给出了光阑半径对实验结果的影响规律,同时对扫描曲线拐点位置的变化规律也进行了详细的讨论。     

双孔干涉效应的量子描述

将一般光束中光子一维态矢量函数应用于光学双孔干涉实验，在几何布置完全对称的情况下，得到这时的光子态矢量函数；     

吡啶盐衍生物双光子吸收性质的理论研究

基于ASPT分子结构,设计了一类具有双重电荷转移结构的二维有机分子生色团,并合成了其中的两种新型分子.实验测试和理论计算结果都表明此类分子在620～1200nm波长范围内没有明显的单光子吸收,因此可在该波段内研究其双光子吸收性质并寻求应用途径.应用量子化学理论中的INDO/CI方法结合计算非线性光学性质的态求和(SOS)方法对此类分子的双光子吸收性质进行了理论研究,结果显示此类分子具有较强的双光子吸收及合适的吸收波长,是一类很有前途的双光子材料.     

应用诱骗态的光子轨道角动量测量设备无关量子密钥分发协议的研究

轨道角动量作为量子信息的一种载体,可应用于测量设备无关量子密钥分发协议中,来消除发送端和接收端间的基校准。诱骗态技术可以消除量子密钥分发协议采用弱相干光源时易被分裂攻击的缺陷。本文将轨道角动量态、测量设备无关方案和诱骗态方案相结合,设计一种基于高效轨道角动量分离方法的诱骗态光子轨道角动量测量设备无关量子密钥分发协议方案,避免了极化方案中对极化基的依赖性缺陷,提高了密钥速率,本文给出了该方案密钥速率的理论推导,并分别对采用无限个诱骗态和两个诱骗态时该方案密钥速率进行了仿真。研究结果表明,在相同条件下,基于轨道角动量的MDI QKD协议方案比极化方案密钥速率更高。      

可用于激光雷达的量子光学技术

为了研究量子关联测量和Hong-Ou-Mandel干涉测量在激光雷达探测上的潜在应用,采用基于色散位移光纤制备关联双光子源的方法和全同光子的Hong-Ou-Mandel干涉原理,搭建了关联双光子产生平台和Hong-Ou-Mandel干涉平台,进行了理论分析和实验检测。结果表明,制备出的关联双光子源,其双光子产生率最高约8kHz,符合/偶然符合计数比最大值约为15,验证了双光子源的量子关联特性;测试了两路弱相干-单光子源的Hong-Ou-Mandel干涉,干涉可见度为0.41±0.01,若将一路光子信号作为激光雷达的回波信号,Hong-Ou-Mandel干涉测量可以将激光雷达的时间测量精度提升到0.95ps±0.03ps,对应空间分辨率为284.06μm±9.94μm。相关实验结果为后续研究不同体制的量子光学-激光雷达技术奠定了基础。     

A quantum multiple access communications scheme using orbital angular momentum

We propose a quantum multiple access communications scheme using Orbital Angular Momentum (OAM) sector states in the paper. In the scheme, each user has an individual modified Poincare Bloch sphere and encodes his information with his own corresponding sector OAM states. A prepared entangled photon pairs are separated at transmitter and receiver. At the transmitter, each user encodes his information with the sector OAM states on the photons and the superposition of the different sector OAM states is carried by the photons. Then the photons are transmitted through quantum noiseless channel to the receiver. At the receiver, each user could retrieve his information by coincidently measuring the transmitted photons with the receiver side photons which are modulated by a special prepared measurement basis. The theoretical analysis and the numerical simulations show that each user could get his information from the superposition state without error. It seems that this scheme provides a novel method for quantum multiple users communications.     

Strain tunable quantum dot based non-classical photon sources

Semiconductor quantum dots are leading candidates for the on-demand generation of single photons and entangled photon pairs.High photon quality and indistinguishability of photons from different sources are critical for quantum information applications.The inability to grow perfectly identical quantum dots with ideal optical properties necessitates the application of post-growth tuning techniques via e.g.temperature,electric,magnetic or strain fields.In this review,we summarize the state-of-the-art and highlight the advantages of strain tunable non-classical photon sources based on epitaxial quantum dots.Using piezoelectric crystals like PMN-PT,the wavelength of single photons and entangled photon pairs emitted by InGaAs/GaAs quantum dots can be tuned reversibly.Combining with quantum light-emitting diodes simultaneously allows for electrical triggering and the tuning of wavelength or exciton fine structure.Emission from light hole exciton can be tuned,and quantum dot containing nanostructure such as nanowires have been piezo-integrated.To ensure the indistinguishability of photons from distant emitters,the wavelength drift caused by piezo creep can be compensated by frequency feedback,which is verified by two-photon interference with photons from two stabilized sources.Therefore,strain tuning proves to be a flexible and reliable tool for the development of scalable quantum dots-based non-classical photon sources.     

The two-photon Rydberg atom micromaser

A Rydberg atom maser operated on a two-photon degenerate atomic transition is discussed. This device combines two interesting features: it is a quantum oscillator working on an intrinsically nonlinear effect and it is a micromaser, with only a few atoms and a few tens of photons at a time in the cavity. The reasons why Rydberg atom-superconducting cavity systems are well adapted for two-photon maser studies are discussed, and the main properties of the device are analyzed by comparing it to Rydberg masers operating on one-photon transitions     

基于线性光学系统实现量子密集编码

在线性光学系统中,提出了一个使用三光子GHZ态实现密集编码的方案。该方案中,Alice首先对她所持有的两个光子通过线性光学元件进行编码,然后将这两个光子传送给Bob. 接收到光子后Bob使用两个QND对等探测器以及PBS光学元件对他拥有的三个光子的八个量子态进行分辨,根据测量的结果辨别出Alice对她的两个光子所进行的操作。在密集编码过程中Alice仅传送两个光子,但Bob可以获得三比特的经典信息。探测使用的QND装置建立在cross-Kerr nonlinearity基础上,目前已经可以通过电磁感应透明实现。     

Quantum signature scheme with single photons

Quantum cryptography combines quantum theorywithclassical cryptography,which provides uncondition-ally secure information exchange by using quantumeffects .Many advances have been made in quantumcryptography in recent years ,including quantum keydistribut…     

用约瑟夫森结量子比特制备簇态

高度纠缠的簇态是一种常见的测量基的量子计算的资源。这里提出了基于约瑟夫森比特的簇态实现方案。方案简单且易于操作,每个量子比特是通过包括一个超导岛和一个库伯对盒来实现的,任意两个约瑟夫森结量子比特可以通过一个对称的直流射频超导干涉仪相互耦合。通过调节每个实现量子比特的的门电压,来设定合适的初态,通过调节系统内相应的参量从而实现一个一个环路的耦合作用,以实现簇态。经过文章理论推导,方案简便易操作。在现在的技术条件下,方案完全可行。     

Partially Loaded Superimposed Training Scheme for Large MIMO Uplink Systems

This paper proposes a new superimposed training (ST) scheme for uplink multi-user multi-cell system, where each base station, equipped with a large number of antennas (M), communicates to single antenna users. In uplink training phase, large number of users within limited coherence time introduces the pilot contamination, which causes two types of interferences in data estimation. The first type, which is referred as self interference, arises due to the dependence between channel estimate and estimation error of the same user, while the second type, known as cross interference, occurs because of the correlation between ST vectors of different users. In this paper, an ST scheme with variable data length is proposed for Rician fading channels. For simplicity of analysis, a single cell model is considered first to derive mean squared error and signal to interference plus noise ratio. The analysis is further extended to multi-cell system. Various limiting cases are investigated, and the design parameters viz., power allocation factor and length of data vector, are optimized. Simulation results verify that the proposed ST scheme reduces self interference, and yields sum rate improvement over conventional ST scheme.     

A New ML Based Interference Cancellation Technique for Layered Space-Time Codes

This paper presents a new and simple decoding algorithm for layered space time block codes such as the two independent Alamouti's codes which are also called the double space-time transmit diversity (DSTTD) system. By using group interference suppression and successive interference cancellation, we can treat DSTTD as two independent space-time block codes (STBC). We can then decode both of these STBC's through a simple maximum likelihood (ML) detector with null space-based interference cancellation. We also compare the proposed interference cancellation (IC) scheme with the conventional MMSE IC scheme. The performance of the proposed IC scheme is comparable to that of the MMSE IC scheme while the complexity reduction factor of the proposed scheme can be up to 5 compared to the MMSE IC scheme.     

Search for Alternative Two-Step-Absorption Photoinitiators for 3D Laser Nanoprinting

Recent studies have opened the door to a new generation of photoinitiators for 3D laser nanoprinting. Therein, the simultaneous absorption of two photons, commonly referred to as two-photon absorption, is replaced by the sequential absorption of two photons in two consecutive one-photon absorption processes. This process has been termed two-step absorption. Importantly, two-step absorption can be accomplished by inexpensive compact low-power continuous-wave blue laser diodes instead of femtosecond laser systems in the red spectral region. Red-shifting the second absorption step with respect to the first one results in an and-type optical nonlinearity based on two-color two-step absorption. Herein, alternatives are systematically explored to the few already reported one- and two-color two-step-absorption photoinitiators, including the search for photoinitiators that can be excited by one-color two-step absorption and be de-excited by a disparate laser color.