四组份不同频率连续变量纠缠态光场的产生

量子纠缠态是开展量子信息工作的核心资源。提出在一块光学超晶格中通过有注入信号的非简并光学参量振荡级联一个和频过程,可以产生不同频率的四组份连续变量纠缠态光场的可行实验方案。首先泵浦光和注入信号光通过差频过程产生闲置光。然后泵浦光和闲置光在同一块光学超晶格中通过级联和频过程产生和频光。根据多组份连续变量纠缠的判定方法,从理论上证明泵浦光、信号光、闲置光与和频光场之间的量子纠缠特性。四组份纠缠特性随泵浦功率的增大而减弱,另外选取较大的注入信号功率、级联非线性过程的耦合参数和泵浦光衰减常数可以得到较好的四组份纠缠光场。该实验方案只用到一块光学超晶格就可以产生四色连续变量纠缠态光场,实验装置简单。     

飞秒脉冲同步泵浦光学参量振荡器中的像散补偿

飞秒脉冲同步泵浦光学参量振荡器(SPOPO)可以产生非经典光学频率梳,在时域多模量子光场基础上,引入光场的空间自由度,可以获得具有时空多模特性的新型压缩态光场。这种多模压缩态可以同时实现波分复用和空分复用,是扩充量子信道容量、实现量子计算的重要工具。由于SPOPO中凹面镜的入射(出射)光线与法线通常具有一定的折叠角,其引入的像散导致某些同阶数高阶模式(例如厄米高斯01和10模)在腔内产生的Gouy相位不同,无法在腔内共振,从而限制了空间多横模压缩态的产生。本文在理论上计算了SPOPO中子午面和弧矢面产生的光束腰斑大小、位置及Gouy相位差,提出了一种补偿像散的方案,实验上实现了SPOPO内的厄米高斯01与10模的同时共振。     

优于12dB压缩态光场的产生与观察

压缩态、振幅压缩态和非经典相关态光场等均为非经典光场。压缩态体现着光场的一种新的量子特性,对它的研究有着重大的科学意义;而且因其电场正交相分量之一的量子噪声可低于散粒噪声极限(shot noise limit简称SNL)在光通信、光计算机、光学精密测量及光谱学、非线性光学中有着十分诱人的应用前景。 继非经典相关态光场产生与观察后,最近作者采用负反馈半导体激光器和平衡零拍探测器成功地产生并观察到了低于散粒噪声极限以下12dB的压缩态光场。本文所报道的产生压缩态光场的实验方案不同于业已报道的参量产生方案(如参量转换、四波混频等):首先实验利用半导体激光器作光源,经分束器将很少一部分光作为信号光束,而其主要部分光作为本振光束。没有用到光学腔,强泵浦光和非线性材料;其次,采用了信号光场量子涨落的     

时域多模飞秒压缩光场测量中的本地光脉冲整形研究

基于飞秒脉冲的同步泵浦参量过程产生的多模时域飞秒压缩光场,由于其独特的优势,特别是可以享有单模光纤网络兼容,是实现可扩展量子计算及大容量量子通讯的良好光源。由于无法实现多模时域飞秒压缩光场的空间分离,目前对于多模时域飞秒压缩光场的测量,采用最为有效的平衡零拍探测。因此如何构造与时域飞秒压缩光场时域函数分布相同的本地光,是其中的关键内容,并直接影响测量效果。本文主要理论研究了本地脉冲光的时域整形方案,分析了系统参数对整形后的多模本地光的保真度以及系统调制效率的影响,并结合实验参数提出可能的解决办法。     

基于低频压缩光的声频信号测量

低频信号测量在引力波探测、生物成像及磁场测量等方面具有重要的应用价值.本文利用非简并光学参量放大器获得了低频压缩态光场,在频率19 kHz处直接测到的压缩度为(7.1±0.1)dB;将产生的正交位相压缩态光场注入到马赫-曾德尔干涉仪中,实现了超越散粒噪声极限(3.0±0.4)dB的声频相位信号的测量.本实验的开展为低频压缩光的产生及基于低频压缩光的声频信号测量提供了一定技术支撑,并且此技术有望扩展到磁场、空间小位移等其他物理量的量子精密测量方案中.     

明亮EPR光束的量子纠缠交换

文中提出一个实现明亮光场量子纠缠交换的理论方案，两个独立的非简并光学参量放大器产生两组经典相干的明亮EPR光束对，通过在每一组EPR光束对的一半上执行联合贝尔态测量，使未产生相互作用的另一半之间产生量子纠缠，在我们的系统中由于采用贝尔态直接探测替代通常的平衡零差探测，不需要本底振荡光，减小了实验难度并能提高探测效率。     

级联倍频过程中谐波场量子噪声压缩的增强

压缩态光场是连续变量量子信息科学研究的重要资源。本文提出了一种利用级联的单共振倍频系统提高压缩度的方案,研究表明两次倍频分别产生的二次谐波与四次谐波场为压缩态光场,且四次谐波场的压缩度比二次谐波场提高了大约3dB。我们还研究了两个谐波场的压缩度随泵浦场衰减率、泵浦功率的变化关系。该系统不仅可以增强压缩态光场的压缩度,而且能将压缩光拓展到更短的波长区域。此外,通过对波长1 014.8nm的基频光进行四倍频获得与汞原子吸收线波长相对应的压缩光场,对量子存储、光谱测量和光频标具有实用价值。     

自发参量下转换实现量子非线性逻辑操作方案

自发参量下转换作为一种重要的非经典光场的产生过程,在基础量子光学实验研究、量子通讯、量子计算等领域有着重要的应用.由于参量过程产生的光场具有单光子量子统计特性,在量子通讯中,在提高信息容量,确保信息安全,避免通讯传输过程中的信号窃取等方面具有经典信息无法比拟的优越性.利用I类BBO晶体作为参量下转换,实验上研究了425 nm飞秒脉冲泵浦的下转换光的量子统计分布,并提出了实现量子非线性逻辑门的可行性方案.     

三组份纠缠与可控连续变量量子密集编码

我们从量子理论出发,提出了利用分束器与非简并光学参量放大器产生三组份量子纠缠态光场[1,2]并用以执行可控连续变量量子密集编码的新方案.在三个组份非局域纠缠的基础上,发送站(Alice)与接收站(Bob)之间的通讯受控于另一指挥部(Claire).实验方案采用明亮的GHZ三组份纠缠光束为信息载体,使用Bell态直接探测方式提取信息,不需要本底振荡光,从而简化了实验系统.所设计的系统可用于量子保密通讯和量子网络.     

级联四波混频系统中纠缠增强的量子操控

各类系统中的纠缠操控是量子信息科学的重要问题之一.本文研究了热原子蒸气的级联四波混频过程中产生的纠缠增强及纠缠增强的相位敏感特性.研究表明,该级联四波混频过程第二级输出的探针光和共轭光的量子纠缠较第一级明显增强,最大可达5 dB以上,且随着强度因子的增大可实现完美纠缠.文中还详细讨论了量子关联类型及纠缠大小与抽运光相位、非线性强度因子之间的变化关系,结果显示,由于纠缠增强及纠缠类型对抽运光相位的敏感性,通过控制相位和强度因子可改变光场噪声特性从而实现对探针光和耦合光之间纠缠增强、纠缠度大小、纠缠类型的量子操控.该理论研究对实验实现纠缠增强及双模压缩态压缩角、压缩度的光学参量操控具有重要的指导意义.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.