Unambiguous State Discrimination in Quantum Key Distribution

The quantum circuit and design are presented for an optimized entangling probe attacking the BB84 Protocol of quantum key distribution (QKD) and yielding maximum information to the probe. Probe photon polarization states become optimally entangled with the signal states on their way between the legitimate transmitter and receiver. Although standard von-Neumann projective measurements of the probe yield maximum information on the pre-privacy amplified key, if instead the probe measurements are performed with a certain positive operator valued measure (POVM), then the measurement results are unambiguous, at least some of the time. It follows that the BB84 (Bennett–Brassard 1984) protocol of quantum key distribution has a vulnerability similar to the well-known vulnerability of the B92 (Bennett 1992) protocol Pacs: 03.67.Dd, 03.67.Hk, 03.65.Ta     

量子计算与量子计算机

量子计算的强大运算能力使得量子计算机具有广阔的应用前景。该文简要介绍了量子计算的发展现状和基本原理,列举了典型的量子算法,阐明了量子计算机的优越性,最后预测了量子计算及量子计算机的应用方向。     

量子安全通信开发回顾

回顾了量子通信协议的发展历程和各个研究方向,重点是量子直接安全通信(QSDC)问题。量子直接安全通信(QSDC)的安全性要求比量子密钥分配(QKD)要高,能够在密文信息泄漏之前察觉到窃听者。基于认证的量子直接安全通信(QSDC)的提出使得量子通信安全性达到了新的高度。     

BB84量子密钥分配协议在专网中的应用

依据专用网络的特点,对BB84量子密钥分配协议做了改进,提出一种适用于专用网络的BB84-PN协议。该协议通过身份认证和量子物理特性,提高了安全性。同时,在通信过程中通过协商传输量子密钥规则,有效地提高了传输效率。     

Coherent state quantum key distribution based on entanglement sudden death

A method for quantum key distribution (QKD) using entangled coherent states is discussed which is designed to provide key distribution rates and transmission distances surpassing those of traditional entangled photon pair QKD by exploiting entanglement sudden death. The method uses entangled electromagnetic signal states of ‘macroscopic’ average photon numbers rather than single photon or entangled photon pairs, which have inherently limited rate and distance performance as bearers of quantum key data. Accordingly, rather than relying specifically on Bell inequalities as do entangled photon pair-based methods, the security of this method is based on entanglement witnesses and related functions.     

QKD网络量子信道管理关键技术研究

随着网络的发展,网络传播的信息日益增多,其中某些信息需要较高的安全性,因此信息加密手段的研究具有重大意义。量子密钥分发(Quantum Key Distribution,QKD)技术基于量子力学中的不可克隆定理,即不可能复制一个未知的量子态而不对其造成扰动,保证了其无条件的安全性,能够实现安全的密钥分发。但目前QKD网络规模较小,不能满足大规模组网的需求。同时,经典网络的路由技术已经不能适应QKD网络,量子信道寻径成为了一个需要解决的问题。鉴于以上问题,提出了一种能够满足较大规模QKD通信的基于光开关切换的QKD网络模型,并重点设计了其网络结构和信令体系,在此基础上设计了一个用于量子信道寻径的先导信号协议,并提出了量子信道管理机制。经实验验证,该模型的性能良好。     

Four-state quantum key distribution exploiting maximum mutual information measurement strategy

We propose a four-state quantum key distribution (QKD) scheme using generalized measurement of nonorthogonal states, the maximum mutual information measurement strategy. Then, we analyze the eavesdropping process in intercept–resend and photon number splitting attack scenes. Our analysis shows that in the intercept–resend and photon number splitting attack eavesdropping scenes, our scheme is more secure than BB84 protocol and has higher key generation rate which may be applied to high-density QKD.     

量子计算与量子计算机

量子计算是一种依照量子力学理论进行的新型计算,量子计算的基础和原理以及重要量子算法为在计算速度上超越图灵机模型提供了可能。在发展与完善量子计算理论的同时,量子计算机的物理实现方案也被不断提出。光子量子计算机,基于核磁共振、离子阱或谐振子等技术的量子计算机物理模型已被逐一实现。近年来亦出现了几个典型的基于量子计算机的量子算法。2001年在一台基于核磁共振技术的量子计算设备上成功演示的Shor量子算法,显示出量子计算机处理复杂问题的巨大潜能。文章对当前量子计算机物理实现的研究进展进行了综述。     

量子密码通信的信号发送与处理系统

自行研制了一套用于量子密码通信的信号发送与处理系统,该系统将自制的半导体激光器驱动电路、相位调制器驱动电路、单光子探测器电路、数据处理及计算机通讯等电路连接起来,与相应光纤光路一起构成了我国第一个光纤量子密码通信系统。     

Securing QKD Links in the Full Hilbert Space

Many quantum key distribution QKD analyses examine the link security in a subset of the full Hilbert space that is available to describe the system. In reality, information about the photon state can be embedded in correlations between the polarization space and other dimensions of the full Hilbert space in such a way that Eve can determine the polarization of a photon without affecting it. This paper uses the concept of suitability Hockney et al. Suitability versus Fidelity for Rating Single Photon Guns to quantify the available information for Eve to exploit, and demonstrate how it is possible for Alice and Bob to fool themselves into thinking they have a highly secure link.PACS:03.67.Dd; 03.67.HK; 42.50.-p.     

The statistical fluctuation study of quantum key distribution in means of uncertainty principle

Laser defects in emitting single photon, photon signal attenuation and propagation of error cause our serious headaches in practical long-distance quantum key distribution (QKD) experiment for a long time. In this paper, we study the uncertainty principle in metrology and use this tool to analyze the statistical fluctuation of the number of received single photons, the yield of single photons and quantum bit error rate (QBER). After that we calculate the error between measured value and real value of every parameter, and concern the propagation error among all the measure values. We paraphrase the Gottesman–Lo–Lutkenhaus–Preskill (GLLP) formula in consideration of those parameters and generate the QKD simulation result. In this study, with the increase in coding photon length, the safe distribution distance is longer and longer. When the coding photon’s length is \(N = 10^{11}\), the safe distribution distance can be almost 118 km. It gives a lower bound of safe transmission distance than without uncertainty principle’s 127 km. So our study is in line with established theory, but we make it more realistic.     

Quantum Malware

When quantum communication networks proliferate they will likely be subject to a new type of attack by hackers, virus makers, and other malicious intruders. Here we introduce the concept of “quantum malware” to describe such human-made intrusions. We offer a simple solution for storage of quantum information in a manner, which protects quantum networks from quantum malware. This solution involves swapping the quantum information at random times between the network and isolated, distributed ancillas. It applies to arbitrary attack types, provided the protective operations are themselves not compromised.     

BB84协议安全判据的实用标准研究

BB84协议是针对单光子量子通信提出的经典协议。在BB84协议安全判据理论值的基础上,结合窃听者所付出成本与其所得信息价值的关系,对自由空间和光纤2种量子信道,分别提出了各自的BB84协议安全判据的实用标准。     

Multiple stochastic paths scheme on partially-trusted relay quantum key distribution network

Quantum key distribution (QKD) technology provides proven unconditional point-to-point security based on fundamental quantum physics. A QKD network also holds promise for secure multi-user communications over long distances at high-speed transmission rates. Although many schemes have been proposed so far, the trusted relay QKD network is still the most practical and flexible scenario. In reality, the insecurity of certain relay sections cannot be ignored, so to solve the fatal security problems of partially-trusted relay networks we suggest a multiple stochastic paths scheme. Its features are: (i) a safe probability model that may be more practical for real applications; (ii) a multi-path scheme with an upper bound for the overall safe probability; (iii) an adaptive stochastic routing algorithm to generate sufficient different paths and hidden routes. Simulation results for a typical partially-trusted relay QKD network show that this generalized scheme is effective. Supported by the National Fundamental Research Program of China (Grant No. 2006CB921900), the National Natural Science Foundation of China (Grant Nos. 60537020 and 60621064), the Knowledge Innovation Project of the Chinese Academy of Sciences, and the Chinese Academy of Sciences International Partnership Project     

基于纠缠的量子密钥分配协议仿真

由于受物理资源和实验条件的限制,在经典计算机上对量子密钥分配（QKD）仿真,为研究者提供一种手段以便更好地掌握这类抽象协议。对以纠缠态为基础的E91协议的量子密钥分配过程进行仿真,重点对比分析了理想环境、有噪环境以及窃听环境下的仿真结果,并验证该量子密钥分配协议的安全性。     

Spin-Based Quantum Dot Quantum Computing in Silicon

The spins of localized electrons in silicon are strong candidates for quantum information processing because of their extremely long coherence times and the integrability of Si within the present microelectronics infrastructure. This paper reviews a strategy for fabricating single electron spin qubits in gated quantum dots in Si/SiGe heterostructures. We discuss the pros and cons of using silicon, present recent advances, and outline challenges. PACS: 03.67.Pp, 03.67.Lx, 85.35.Be, 73.21.La     

Controlling Spin Qubits in Quantum Dots

We review progress on the spintronics proposal for quantum computing where the quantum bits (qubits) are implemented with electron spins. We calculate the exchange interaction of coupled quantum dots and present experiments, where the exchange coupling is measured via transport. Then, experiments on single spins on dots are described, where long spin relaxation times, on the order of a millisecond, are observed. We consider spin-orbit interaction as sources of spin decoherence and find theoretically that also long decoherence times are expected. Further, we describe the concept of spin filtering using quantum dots and show data of successful experiments. We also show an implementation of a read out scheme for spin qubits and define how qubits can be measured with high precision. Then, we propose new experiments, where the spin decoherence time and the Rabi oscillations of single electrons can be measured via charge transport through quantum dots. Finally, all these achievements have promising applications both in conventional and quantum information processing. PACS: 03.67.Lx, 03.67.Mn, 73.23.Hk, 85.35.Be     

Topical Review: Optimum Probe Parameters for Entangling Probe in Quantum Key Distribution

For the four-state protocol of quantum key distribution, optimum sets of probe parameters are calculated for the most general unitary probe in which each individual transmitted photon is made to interact with the probe so that the signal and the probe are left in an entangled state, and projective measurement by the probe, made subsequent to projective measurement by the legitimate receiver, yields information about the signal state. The probe optimization is based on maximizing the Renyi information gain by the probe on corrected data for a given error rate induced by the probe in the legitimate receiver. An arbitrary angle is included between the nonorthogonal linear polarization states of the signal photons. Two sets of optimum probe parameters are determined which both correspond to the same optimization. Also, a larger set of optimum probe parameters is found than was known previously for the standard BB84 protocol. A detailed comparison is made between the complete and incomplete optimizations, and the latter simpler optimization is also made complete. Also, the process of key distillation from the quantum transmission in quantum key distribution is reviewed, with the objective of calculating the secrecy capacity of the four-state protocol in the presence of the eavesdropping probe. Emphasis is placed on information leakage to the probe. PACS: 03.67.Dd; 03.67.Hk; 03.65.Ta     

Quantum probabilistically cloning and computation

In this article we make a review on the usefulness of probabilistically cloning and present examples of quantum computation tasks for which quantum cloning offers an advantage which cannot be matched by any approach that does not resort to it. In these quantum computations, one needs to distribute quantum information contained in states about which we have some partial information. To perform quantum computations, one uses state-dependent probabilistic quantum cloning procedure to distribute quantum information in the middle of a quantum computation. And we discuss the achievable efficiencies and the efficient quantum logic network for probabilistic cloning the quantum states used in implementing quantum computation tasks for which cloning provides enhancement in performance.