基于周期极化KTiOPO4晶体的高亮度纠缠源研制

量子纠缠是量子信息领域的核心资源,目前利用β型硼酸钡(BBO)晶体参量下转换制备的纠缠光子对的亮度较低,它直接制约了量子通信的最远距离,已无法满足星地实用化量子通信的发展需求.利用周期极化KTiOPO4晶体,采用准相位匹配技术设计产生了一种后选择的纠缠源,测得的符合计数达到了16×103s-1 mW-1,极化对比度达到27∶1,在亮度上比基于BBO的量子纠缠光源提高了一个数量级以上.这一高亮度的纠缠源可以广泛应用于量子密钥分发、量子隐形传态以及量子计算等新兴量子信息领域,为实现全球化量子通信提供了有力的保障.     

理论构造周期极化KTiOPO_4晶体制备852和1550nm双色纠缠光

利用KTiOPO4(KTP)材料非线性系数d33对应的二阶非线性0-类准相位匹配,理论上设计构造了一种周期极化KTiOPO4晶体(PPKTP),当晶体温度为20℃时,晶体准相位匹配格子的周期为10.70μm。波长为550nm的激光泵浦由该晶体组成的光学参量振荡器能产生含852nm信号光和1550nm的闲置光的双色纠缠,其中信号光对应Cs原子吸收线,闲置光1550nm对应光纤通讯波长。该纠缠光对量子信息网络和原子信息存储有非常重要的意义。     

基于光子晶体光纤的高纯度量子关联光子对的制备

使用脉冲光在室温下抽运一根长1 m 的高非线性光子晶体光纤, 产生了中心波长分别位于830 nm 和1411 nm的具有量子关联性的闲频与信号光子. 实验中闲频和信号通道的带宽分别是15 nm和35 nm. 对单通道光子计数率的拟合结果显示光子几乎全部来源于光纤中的自发四波混频过程, 未受到Raman散射噪声的影响. 当闲频和信号通道的光子产生率约为每脉冲0.0085个时, 测得符合计数率与随机符合计数率的比值为102, 接近理论极限, 不仅证明了光子对的低噪声性, 而且表明所产生的光子对本身具有窄带频谱特性, 因而实验中对其收集效率很高. 此外, 这种高纯度关联光子对还联接了不同波段, 在量子信息技术中有着潜在的应用.     

基于周期极化KTiOPO$lt;sub$gt;4$lt;/sub$gt;晶体的高亮度纠缠源研制

量子纠缠是量子信息领域的核心资源,目前利用β型硼酸钡（BBO）晶体参量下转换制备的纠缠光子对的亮度较低,它直接制约了量子通信的最远距离,已无法满足星地实用化量子通信的发展需求.利用周期极化KTiOPO₄晶体,采用准相位匹配技术设计产生了一种后选择的纠缠源,测得的符合计数达到了16×10³s^-1 mW^-1,极化对比度达到27∶1,在亮度上比基于BBO的量子纠缠光源提高了一个数量级以上.这一高亮度的纠缠源可以广泛应用于量子密钥分发、量子隐形传态以及量子计算等新兴量子信息领域,为实现全球化量子通信提供了有力的保障. 关键词： 纠缠态 准相位匹配 4晶体')" href="#">周期极化KTiOPO₄晶体     

基于光子晶体光纤关联光子对频谱特性的研究

为了研究光子品体光纤在800 nm波段关联光子对的频谱特性.基于自发四波混频得到了脉冲抽运光产生的光子对的相位匹配函数和频谱甬数.数值计算、证明闲频光中心波长取796 nm时的频谱对称性最好;在假设闲频光频率为单一频率的前提下,利用简化频谱函数的表达式,通过改变光子晶体光纤零色散点色散斜率和非线性系数,以及抽运光的入射中心波长,进一步讨论了抽运光和光子晶体光纤参数变化对信号光和闲频光频谱函数的影响及变化规律.提出了有利于产生高纯度纠缠光子对的光纤参数和抽运光参数,结果对于在800 nm波段发展光子晶体光纤纠缠光子源的实验具有指导和参考意义.     

准晶非线性光子晶体中二次谐波波长和温度调谐的研究

在八重准周期极化的铌酸锂非线性光子晶体中,通过调节基频光波长实现了多个波长的同时共线准相位匹配倍频,最高转换效率达36%.同时,测量了准晶非线性光子晶体中二次谐波转换效率随晶体温度以及入射波长的变化,结果表明二次谐波在长波处具有更宽的温度以及波长调谐带宽.该项研究对于准周期非线性光子晶体在实际工作中的运用具有重要的指导意义. 关键词： 准周期 非线性光子晶体 温度调谐 波长调谐     

基于MgO∶PPLN晶体差频产生的宽调谐中红外连续激光光源

分别以1 083nm和1 550nm波段的窄线宽连续光源为泵浦光和信号光,搭建基于掺MgO周期铌酸锂晶体(MgO∶PPLN)准相位匹配原理的差频非线性效应产生中红外激光实验系统.根据系统温度和信号光波长调谐特性进行实验研究.在泵浦光波长固定条件下改变信号光波长,实现了窄线宽宽调谐中红外连续闲频激光输出,波长覆盖范围为3 547.6~3 629.1nm.当波长为1 082.8nm的泵浦光和波长为1 549.7nm的信号光功率分别放大到2.8 W和3.5 W时,对波长为3 597.0nm的中红外闲频光输出进行长时间功率扫描监测,得到最大功率为3.2mW,功率抖动引起不稳定度小于±1.6%的高稳定的中红外窄线宽激光输出.该研究结果可为设计和研制多波长窄线宽中红外光源提供参考.     

光纤激光泵浦MgO:PPLN高功率中波红外光参量振荡器

为实现高效率、高功率中波红外激光输出,研制基于MgO:PPLN晶体的中波红外光参量振荡器（OPO）,泵浦源为基于主振荡功率放大（MOPA）结构的线偏振掺Yb光纤激光器（YDFL）。实验结果表明:YDFL可实现最高79.1 W的1064.1 nm脉冲线偏振激光输出;在YDFL泵浦下,通过优化输出镜曲率半径和泵浦光束腰直径,该OPO实现最高9.15 W的3.754 μm脉冲激光输出,光光转换效率为11.57%,重复频率为300 kHz,脉冲宽度约为110 ns。     

利用纠缠密度研究光子禁带系统的纠缠演化特性

研究了一个二能级原子在光子禁带模型中的原子与热库间及热库模式间的纠缠动力学行为.利用全局纠缠的方法,引出与热库模式相关的纠缠密度.研究发现,当禁带是完美带隙时,会出现稳态原子布居数俘获现象,从而抑制原子的自发辐射效应,防止了信息传输过程中信息的流失.原子与热库模式之间的纠缠密度以及热库模式与模式之间的纠缠密度会随着原子与热库之间耦合强度的增加而增大.当取长时极限时,原子与热库模式之间的纠缠减为零.热库模式与模式之间在强耦合情况下,由于拉比分裂的作用,在两个对称模式间会形成较强的纠缠;在弱耦合情况下,只能在中心频率处形成纠缠.     

基于部分纠缠光子源的高效量子密钥分配方案

设计了一种高效的部分纠缠光子对产生装置,这套装置中使用了简单的线性光学元件以及双光子吸收介质(TPAM),在文中讨论了TPAM的一种实现方案.我们把此种装置应用于量子密钥分配方案,分析了其效率和安全性,相比于用自发参量下转换(SPDC)产生纠缠光子对的密钥分配方案,该方案有更高的效率和安全性.     

Degenerate entangled photon pairs source based on PPLN waveguide for quantum computation

Integrated photonic devices are expected to play a promising role in the field of quantum information science. In this paper we propose two schemes for generating polarization-mode entangled photon pairs based on titanium-indiffused waveguide on periodically polled lithium niobate by using simultaneous quasi-phase-matching of Type-I and higher order Type-0 spontaneous parametric down conversion processes in one of them and Type-II in another. The photon pairs are emitted at the wavelength of 812 nm suitable for quantum computation applications within a bandwidth of 14 and 0.2 nm, and the generation rate of the degenerate sources is 44,360 and 91 pairs/(s GHz mW) respectively, in a 1-cm long waveguide. These degenerate sources can provide maximally entangled photon pairs as the Tangle of the sources is as high as 0.9999 and 1, accordingly.     

基于偏振纠缠光子对的单光子源

提出了一种基于参量下转换纠缠光子对获得单光子源的实验方案,并对实验的光路、数据采集方面做了详细介绍.实验结果显示,由此方案获得的单光子源的品质要优于弱相干光式的单光子源两个数量级,即多光子光脉冲出现的概率降低了100倍.实验结果表明此方案有望得到实际应用. 关键词： 单光子源 参量下转换 反符合测量     

Observations of dispersion cancellation of entangled photon pairs

An experimental study of the dispersion cancellation occurring in frequency-entangled photon pairs is presented. The approach uses time-resolved up-conversion of the pairs, which has temporal resolution at the femtosecond level, and group-delay dispersion sensitivity of ≈ 20 fs2 under experimental conditions. The cancellation is demonstrated with dispersion stronger than ± 10(3) fs2 in the signal (-) and idler (+) modes.     

Fiber-based telecom-band degenerate-frequency source of entangled photon pairs

We demonstrate the generation of polarization-entangled photon pairs of degenerate frequency for the first time, to the best of our knowledge, in standard optical fiber using a novel dual-pump, counterpropagating configuration. Two-photon interference with >97% visibility is obtained. The purity of the photon source, as characterized by the ratio of coincidence to accidental-coincidence counts, is shown to be as high as 116 under suitable operating conditions.     

Diffraction of entangled photon pairs by ultrasonic waves

In this paper, we have presented and established a new theoretical formulation of photon optics based on photon path and Feynman path integral idea. We have used Feynman path integral approach to discuss Fraunhofer, Fresnel diffraction of single photon and entangled photon pairs by ultrasonic wave and obtained the following results: i) quantum state and probability distribution of single photon and entangled photon pairs by Fraunhofer and Fresnel ultrasonic diffraction, ii) oblique incidence Raman-Nath and Bragg diffraction conditions, iii) total correlation state and its probability distribution. Our calculation results are in agreement with the experiment results. Comparing one-photon and two-photon diffraction effects by ultrasonic waves, we have found that two-photon diffraction by ultrasonic waves is also a sub-wavelength diffraction.     

Experiments of quantum nonlocality with polarization-momentum entangled photon pairs

We present the results of some experimental tests of quantum nonlocality performed by two-photon states, entangled both in polarization and momentum, namely hyperentangled states and two-photon four-qubit linear cluster states. These states, which double the number of available qubits with respect to the standard two-photon entangled states, are engineered by a simple experimental method, which adopts linear optics and a single type I nonlinear crystal. The tests of local realism performed with these states represent a generalization of the Greenberger, Home, and Zeilinger (GHZ) theorem to the case of two entangled particles.     

High-efficiency mid-infrared laser from synchronous optical parametric oscillation and amplification based on a single MgO:PPLN crystal

This paper presents a specially designed optical parametric oscillator (OPO) which achieved high-efficiency mid-infrared laser of 2.83 μm. The cascaded nonlinear interactions of OPO and optical parametric amplifier (OPA) were simultaneously realized in a single MgO:PPLN crystal. The signal oscillation of 1.70 μm was used to pump a secondary parametric process that resulted in amplification of the idler laser of 2.83 μm. When the MgO:PPLN crystal with a grating period of 31.2 μm was pumped by a 1.064 μm laser and operated at 148°C, the quasi-phase-matching of both OPO and OPA could be simultaneously achieved. Average output power of 7.68 W at 2.83 μm was obtained for 25 W of pump at 7 kHz. The power conversion efficiency of 2.83 μm laser was 30.7%, which was evidently higher than common OPOs.     

Generation of high-purity telecom-band entangled photon pairs in dispersion-shifted fiber

We study the purity of correlated photon pairs generated in a dispersion-shifted fiber at various temperatures. The ratio of coincidence to accidental-coincidence counts greater than 100 can be obtained as the fiber is cooled to liquid-nitrogen temperature (77 K). We then generate polarization-entangled photon pairs by using a compact counterpropagating scheme. Two-photon interference with visibility >98% and Bell's inequality violation by >8 standard deviations of measurement uncertainty are observed at 77 K, without subtracting the accidental-coincidence counts due to background Raman photons.