量子保密通信用准单光子源的研制

量子保密通信是一种以基本粒子的量子力学性质为依据，在理论上证明是绝对安全的密钥分配技术。其绝对安全性引起了国内外的高度重视。要实现量子保密通信有两大关键技术——单光子脉冲技术和单光子探测技术．单光子是量子保密通信的基础，如果通信信道中含有两个或多个光子，则窃听者就可能截取多余的光子进行检测而不被知晓，从而     

简并拉曼过程中量子保真度的演化

保真度是量子光学和信息光学中的一个重要概念，保真度的研究对量子通信和量子计算领域的发展有重要意义。运用全量子理论研究了考虑斯塔克位移的简并拉曼耦合模型中，斯塔克参数和平均光子数对量子态保真度和保真度振幅的影响，并对这种影响做出解释。结果表明，斯塔克常数越小，原子和光场的关联就越弱，系统、光场和原子的保真度就越大；平均光子数越大，原子和光场的相互作用就越强，系统和原子的保真度就越小．     

光子轨道角动量在量子通信中应用的研究进展

轨道角动量是光子的量子态,具有轨道角动量的光束在光通信等领域中得到了广泛的应用,是目前国内外研究的热点方向之一,特别是轨道角动量可作为自由空间量子信息物理载体的重要选择,这将对量子通信领域带来重要的影响。介绍了光子轨道角动量的定义、产生,简要列举当前的相位、偏振编码经典的两类量子密码通信方案以作对照,以提出的光子轨道角动量密码通信方案为例,着重介绍了光子轨道角动量在量子通信中的应用研究及展望。     

1 550 nm升频单光子探测器的特性分析

分析了一种工作波长为1550 nm,利用铌酸锂周期极化波导和硅雪崩二极管构成的升频单光子探测器的性能,给出了应用这种探测器的理想通信系统的结构组成,讨论了升频单光子探测器主要参数:量子效率和暗记数及其与泵浦功率的关系.通过比较得出升频探测器优于传统的InGaAs/InP雪崩二极管单光子探测器,能很好地改善量子通信系统的性能.     

媒体扫描

超亮度可调谐光子对源在美国麻省理工学院建立的超亮度可调谐光子对源是至今最好的纠缠光子对发生器,这一进展会使量子通信系统做得更顺利。纠缠光子具有特殊的相关性,这与经典物理中的情况不同。例如,如果我们测量,其中一个光子的自旋(偏振),则可自动地知道另一个光子的偏振,即使它可能在星系的另一边,两光子自旋是不确定的。量子实体的这种神秘特性,希望对密码学(“量子远程传物”的可能机理)和未来的量子计算机大有裨益。的确,目前在通信工程应用中,量子效应曾一度起重要作用,特别是在量子起伏(就我们的知识而言,无法知道电子的位置和它…     

单光子卫星量子通信噪声和干扰分析

卫星量子通信是建立全球量子通信网络的最佳选择之一。针对采用偏振编码的卫星量子通信中的偏振保持问题,研究了大气散射和卫星与地面站间相对运动等因素对量子偏振态相位和对准的影响以及相位延迟和对准误差对系统量子误码率的影响,分析了背景噪声和系统硬件噪声对通信产生的影响以及单光子通信过程中可能受到的光子分离攻击干扰,为量子信号认知设计提供借鉴意义。     

长距离长时间稳定的量子保密通信系统

量子密码术是迄今为止唯一被理论证明绝对安全的保密通信方案。随着计算机网络对信息安全的要求不断提高，国际上许多研究组都将量子保密通信研究的重点放在了光纤通信系统上．在最近的实验中，我们试制完成了基于“即插即用”设计的光纤量子保密通信样机．该系统实验发展了一种新型门限脉冲驱动的符合单光子探测技术，并且在激光发射     

中国科大完成最远距离自由空间量子通信实验

中国科技大学、合肥微尺度物质科学国家实验室潘建伟教授和同事杨涛、彭承志等人，通过“自由空间纠缠光子的分发”在国际上首次证明，纠缠光子在穿透等效于整个大气层厚度的地面大气后，其纠缠特性仍能保持，并可应用于高效、安全的量子通信。这一研究成果为实现全球化的量子通信奠定了实验基础。     

APD单光子探测技术

单光子探测器是量子保密通信的主要器件，同时也是量子通信中重要的研究课题．本文分别介绍了量子保密通信用APD单光子探测技术及其工作在无源抑制、有源抑制和门模式下的基本工作特性，分析了他们各自的优缺点及其未来的发展方向．     

安全稳定实用的差分量子密钥分配实验研究

在差分密钥分配通信系统中,嵌入时分复用单光子探测装置,在每次量子密钥分配的同时计量发信者(Alice)用于密钥分配的单脉冲平均光子数,确保通信的安全程度.实现了90 km的稳定的量子保密通信,误码率约为4%,有很好的实用价值.     

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.     

Role of Cooper pairs for the generation of entangled photon pairs from single quantum dots

Generation of entangled photon pairs from semiconductor quantum dots (QDs) is highly desirable for realizing practical solid-state photon sources for quantum information processing and quantum cryptography. However, the energy splitting of exciton states in QDs almost prevent the generation of entangled photon pairs. This paper discusses the new possibility with the injection of electron as well as hole Cooper pairs into QDs.     

用三粒子纠缠态和Bell态作量子信道实现非局域的态交换

提出一种用三粒子纠缠态和Bell态作量子信道对处于异地的两纠缠粒子对实现非局域的态交换的理论方案.该方案的特点是,两地之间还存在一位第三者,她作为监控人参与量子非局域操纵过程.特别地,当量子信道为部分纠缠态时,此人可矫正被非理想量子信道致畸的量子态.     

Subminiature emitters based on a single (111) In(Ga)As quantum dot and hybrid microcavity

The results of numerical modeling and investigation of a hybrid microcavity based on a semiconductor Bragg reflector and a microlens selectively positioned above a single (111) In(Ga)As quantum dot are presented. Emitters based on the hybrid microcavity demonstrate the effective pumping of a single quantum dot and high emission output efficiency. The microcavity design can be used to implement emitters of polarization- entangled photon pairs based on single semiconductor quantum dots.     

面向长距离量子通信的双光子关联成像技术

量子时域鬼成像利用光子对的时间-频率关联性实现了50km光纤链路上的图像传送,有望应用于量子通信的协议中。然而,现有方案的成像质量较差,成像速度较慢,因此其应用性在一定程度上受到了限制。文章对已有成像方案进行了较大的改进,利用可编程滤波器数字设定待成像信息,进而实现了二维图像信息的自动化实时传送。实验结果证明,改进方案的成像质量和速度均有显著改善,有利于推动量子关联成像在量子通信领域的应用。     

Quantum teleportation with a single-photon wave packet

A scheme of energy—time quantum teleportation using an entangled photon pair is proposed. The teleportation of a multimode state of a single-photon wave packet is investigated theoretically.     

基于四粒子纠缠态的量子秘密共享方案

基于2个不同的四粒子纠缠态分别提出了三方、四方量子秘密共享方案,其中采用的秘密信息是一个相同的未知两粒子纠缠态。在量子秘密共享方案中发送者对所拥有的粒子实施适当的Bell态（或GHZ态）测量,发送者和合作者通过经典通讯把测量结果告知信息接收者,接收者在其他合作者的协助下通过实施相应的量子操作完成对初始量子态信息的重构。对所提出的2个方案进行了讨论和比较,发现四方量子秘密共享方案的安全性更加可靠。     

Quantum-Dot Sources for Single Photons and Entangled Photon Pairs

Quantum dots show excellent promise as triggered sources of both single and polarization entangled photons for quantum information applications. Our recent progress developing nonclassical light sources with single quantum dots is presented in this paper. Following radiative emission of an exciton confined in a quantum dot, there is a finite delay before re-excitation can occur; this results in an anti-bunching of the photons emitted providing a source of single photons. Excitation of a quantum dot with two electrons and two holes leads to the emission of a pair of photons; we show here that, provided the spin splitting of the intermediate exciton state in the decay is erased, the photon pair is emitted in an entangled polarization state. The fidelity of this entangled state is shown to exceed 70%. Using quantum dots to generate quantum light allows contacts for electrical injection to be integrated into a compact and robust device. A cavity may also be integrated into the semiconductor structure to enhance the photon collection efficiency and control the recombination dynamics. We detail a process to form a submicrometer current aperture within an electrical device, allowing individual quantum dots to be addressed electrically in devices.     

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…