基于纠缠光子对的真随机数源

介绍了理论上基于量子力学的基本原理、实验方面基于新型的单光子源即参量下转换所产生的纠缠光子对,单光子路径自由选择产生真随机数序列的实验[1].     

基于偏振关联光子对的量子密码术实验方案

本文提出了一种用参量下转换光子对振偏纠缠的特性实现的量子密码术实验方案，同Ｅｋｅｒｔ提出的基于参量下转换光子对时空纠缠特性的实验方案相比，本方案省掉了两个复杂的Ｍａｃｈ－Ｚｅｎｈｄｅｒ干涉仪和两个昂贵的单光子探测器，简化了系统装置。     

六光子超纠缠态制备方案

自发参量下转换对应于一种非线性光学过程, 实验上作为一种标准方法, 人们利用自发参量下转换源产生纠缠光子对. 本文考虑由自发参量下转换源产生三对纠缠光子的情况. 通过使用由几组偏振光 束分束器、分束器和半波片等线性光学器件组成的量子线路演化三对光子, 给出了一个高效制备 包含偏振纠缠和空间纠缠的六光子超纠缠态方案. 因为方案中包含了参量下转换源产生三对纠缠光子 的所有可能情况, 所以本方案有很高的效率. 基于弱非线性介质构建了一个量子非破坏性测量装置, 用于区分光子在两指定的空间模中的两种分布情况. 特别地, 方案中可以通过合理约束在量子非破坏性测量过程中引入的非线性强度来达到实际实验所限定的数量级, 因此, 该方案易于在实验上实现.     

自发参量下转换过程光场分布

单光子的产生与测量在量子物理、量子信息研究中都有非常重要的意义.本文利用中心波长为850nm的飞秒脉冲二次谐波425 nm泵浦I类非共线相位匹配BBO晶体,获得非共线简并自发参量下转换(SPDC)光.实验测量了下转换光的空间分布、光子数分布和符合计数率.并进一步通过符合计数方法测量了获得单光子的几率.     

基于条件参量下转换光子对的非正交编码诱惑态量子密钥分发

诱惑态方法和非正交编码协议可以有效的抵制光子数分束攻击,所以近来得到了广泛的关注.这里结合了这两种方法提出了一种新方案,光源采用呈泊松分布的参量下转换光子对,发送方随机的改变抽运光的强度获得不同强度的信号光,信号态用来产生密钥,诱惑态用来监测窃听,并估算单光子和两光子的计数率和量子误码率,模拟了密钥产生率与传输距离的关系曲线,分析了该方案可以进一步提高安全量子密钥分发的性能.     

自发参量下转换双光子场绝对校准光电探测器的方法研究

讨论了一种基于自发参量下转换双光子场绝对校准光电探测器灵敏度的新方法,着重推导了对自发参量下转换过程中产生的单光子的探测概率和双光子的符合速率,从而阐明了绝对测量光电探测器量子效率的原理.基于这一方法对光子计数型光电倍增管的响应灵敏度进行了测量,并将实验结果与常规方法测得的结果进行了比较. 关键词：     

一种新的预报单光子源诱骗态量子密钥分发方案

提出一种新的预报单光子源诱骗态量子密钥分发方案.在发端采用参量下变换产生纠缠光子对,其中之一用来进行预报探测,根据探测结果将另一路光脉冲分成两个集合,其中预报探测有响应的脉冲集合用作信号态,无响应的脉冲集合作为诱骗态.由于探测效率的问题,这两个集合都是有光子的,通过这两个集合的通过率和错误率估计出单光子的通过率和错误率.此方法不需要改变光强,简单可行.仿真结果表明：该方法可以达到完美单光子源的安全通信距离;与预报单光子源的量子密钥分发相比,密钥产生率有了很大的提高;和三强度预报单光子源诱骗态量子密钥分发的 关键词： 量子保密通信 量子密钥分发 诱骗态 预报单光子源     

单光子探测器量子效率的自绝对标定

单光子探测器日益广泛地应用于科学研究的各个领域，精确地标定其量子效率成为应用的先决条件。我们首次实现了单光子探测器量子效率自绝对标定的原理性实验，即只利用待测探测器本身就可以对其量子效率进行绝对标定，而不需要第二个探测器或任何参考标准。该方法基于自发参量下转换产生的纠缠光子对的时间关联性，在信号光子和闲散光子之间引入延时，由单光子计数率和符合计数率测得探测器的量子效率。     

光子计数器的线性测量和修正

依据自发参量下转换过程中泵浦光功率和相关光子的线性关系,搭建了光子计数器线性测量实验装置,分析了光子计数器非线性误差产生的机理,探讨其线性应用条件和修正方法.通过调节泵浦光功率改变入射至光子计数器的相关光子速率,实现了光子计数器线性的测量,并对实验测量值进行了修正.结果表明,通过线性测量和修正可以提高单光子计数器测量准确度,降低光子计数器的非线性误差,其入射光子速率最大线性工作范围可由10~5s~(-1)扩大到10~7s~(-1).     

基于光子间隙随机分布的真随机数源

提出了利用模数转换器提高真随机数源速率的方案, 该方案基于衰减脉冲激光光子间隙随机分布, 可使随机数的产生速率提高十几倍.实验中将时间幅度转换仪与16位模数转换器相结合, 产生的各比特位随机数序列顺利通过了国际通用的随机数检测程序统计测试标准, 该方案实验装置简单, 增强了系统的抗干扰能力. 关键词： 衰减式单光子源 模数转换 延时符合 随机数检测     

Linear-optical processing cannot increase photon efficiency

We answer the question whether linear-optical processing of the states produced by one or multiple imperfect single-photon sources can improve the single-photon fidelity. This processing can include arbitrary interferometers, coherent states, feedforward, and conditioning on results of detections. We show that without introducing multiphoton components, the single-photon fraction in any of the single-mode states resulting from such processing cannot be made to exceed the efficiency of the best available photon source. If multiphoton components are allowed, the single-photon fidelity cannot be increased beyond 1/2. We propose a natural general definition of the quantum-optical state efficiency, and show that it cannot increase under linear-optical processing.     

Cavity-free photon blockade induced by many-body bound states

The manipulation of individual, mobile quanta is a key goal of quantum communication; to achieve this, nonlinear phenomena in open systems can play a critical role. We show theoretically that a variety of strong quantum nonlinear phenomena occur in a completely open one-dimensional waveguide coupled to an N-type four-level system. We focus on photon blockade and the creation of single-photon states in the absence of a cavity. Many-body bound states appear due to the strong photon-photon correlation mediated by the four-level system. These bound states cause photon blockade, which can generate a sub-Poissonian single-photon source.     

Single photon sources with single semiconductor quantum dots

In t.his contribution, we briefly recall the basic concepts of quantum optics and properties of semicon- ductor quantum clot. （QD） which a.re necessary to the nnderstanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantmn emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as opti- cal properties of the QDs. We then review the localizatioll of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and perfornances in terms of strong coupling regime, elfieiency, directionality, and polarization control. Furthermore, we will discuss the recenl, progress on the fabrication of single photon sources, and various a.pproaehes for embedding single QDs into mieroca,vities or photonic crystal nanoeavities and show how to ex- tend the wavelength range. We focus in part;icular on new generations of electrically driven QD single photon source leading to high repetition rates, efficiencies at elevated temperature operation. Besides strong eoupling regime, and high collection new development;s of room temperature sin- gle photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for pract ical single-photon sources are also discussed.     

Passive decoy-state quantum key distribution for the weak coherent photon source with finite-length key

Passive decoy-state quantum key distribution systems, proven to be more desirable than active ones in some scenarios,also have the problem of device imperfections like finite-length keys. In this paper, based on the WCP source which can be used for the passive decoy-state method, we obtain the expressions of single-photon error rates, single-photon counts, and phase error rates. According to the information of smooth min-entropy, we calculate the key generation rate under the condition of finite-length key. Key generation rates with different numbers of pulses are compared by numerical simulations. From the results, it can be seen that the passive decoy-state method can have good results if the total number of pulses reaches 1010. We also simulate the passive decoy-state method with different probabilities of choosing a pulse for parameter estimation when the number of pulses is fixed.     

Quantum key distribution using quantum-correlated photon sources

Quantum key exchanges using weak coherent (Poissonian) single-photon sources are open to attack by a variety of eavesdropping techniques. Quantum-correlated photon sources provide a means of flagging potentially insecure multiple-photon emissions and thus extending the secure quantum key channel capacity and the secure key distribution range. We present indicative photon-counting statistics for a fully correlated Poissonian multibeam photon source in which the transmitted beam is conditioned by photon number measurements on the remaining beams with non-ideal multiphoton counters. We show that significant rejection of insecure photon pulses from a twin-beam source cannot be obtained with a detector having a realistic quantum efficiency. However quantum-correlated (quadruplet or octuplet) multiplet photon sources conditioned by high efficiency multiphoton counters could provide large improvements in the secure channel capacity and the secure distribution range of high loss systems such as those using the low earth orbit satellite links proposed for global quantum key distribution. Received 14 July and Received in final form 20 November 2001     

量子通信中单光子探测器的实验研究

为了提高单光子探测系统的灵敏度,实验采用InGaAs/InP雪崩光电二极管作为量子通信中的单光子探测器件,以门控脉冲模式实现了更高精度的单光子探测器的偏压生成电路、单光子信号放大电路、单光子信号检测电路和温度控制模块,并通过选用高精度前置放大器OP37和精密比较器AD8561,将量子效率提高到18.3%,暗计数控制小于4.1%×10~(-6)/ns.     

Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks

Highly correlated photons or, accordingly, high-fidelity single-photon states are a prerequisite for closing detection loopholes in experimental tests of local realism and implementing scalable linear optical quantum computation. We demonstrate a parametric down-conversion source exhibiting a conditional detection efficiency of 51% (with corresponding preparation efficiency of 85%) and extraordinarily high detection rates of up to 8.5 x 10(5) coincidences/(s mW). We exploit a novel type-II phase matching configuration in a microstructured waveguide in conjunction with an ultrashort pump.     

Entangled photon holes

Most experimental demonstrations of entanglement require nonclassical states and correlated measurements of single-photon detection events. It is shown here that entanglement can produce a large decrease in the rate of two-photon absorption for a classical input state that can be observed using classical detectors. These effects can be interpreted as being due to the creation of entangled photon holes that are somewhat analogous to the holes of semiconductor theory.     

Performance of a superconducting single photon detector with nano-antenna

<正>The performance of single-photon detectors can be enhanced by using nano-antenna.The characteristics of the superconducting nano-wire single-photon detector with cavity plus anti-reflect coating and specially designed nanoantenna is analysed.The photon collection efficiency of the detector is enhanced without damaging the detector’s speed,thus getting rid of the dilemma of speed and efficiency.The characteristics of nano-antenna are discussed,such as the position and the effect of the active area,and the best result is given.The photon collection efficiency is increased by 92 times compared with that of existing detectors.     

Nanoscale solid-state single photon router

A novel scheme for a solid-state single-photon router based on a single quantum dot (QD) coupled to a nanomechanical resonator (NR) is proposed and analyzed theoretically. It relies on the coherent coupling between the quantum dot and the NR. We demonstrate that when a single-photon signal is tuned on resonance with the exciton in the QD, one can use a strong pump field to choose to what output port of this signal field is delivered, which is based on the analogue of electromagnetically induced transparency (EIT) effect which we refer it as phonon induced transparency (PIT) in this coupled system. The path between the reflection output port and the transmission output port can be achieved by simply turning off and on the pump field. The numerical results also indicate that this router can operate efficiently in the optical regime and at ultralow pump power as well as short switching time (～ns). This nanoscale router presented here will offer potential applications in scalable solid-state quantum networks and quantum information.