1550 nm单模光纤中的量子密钥分配

从实验中实现了红外波段的远程量子密钥分配。系统采用双不等臂M-Z干涉仪相位编码方式,工作波长为1550nm。通过分析量子密钥分配系统传输距离与误码率之间相互关系,给出了理论上理想不等臂M-Z系统与实际系统的最低误码率与传输距离间的关系,以及系统实测传输距离与误码率的关系。实验结果显示,本密钥分配系统已非常接近理想实验系统的性能。     

基于光纤的量子密钥分配系统研究和协议仿真

研究了适合光纤传输的量子密钥分配系统和量子密钥分配协议.通过研究适合光纤传输的量子信号的编码和解码,研究了基于光纤的量子密钥分配系统与协议,给出相位调制量子密钥系统的光路图;在计算机上编制相应的程序,验证了相位调制的量子密钥分配协议的分配过程,并就窃听对量子误码率的影响进行了分析.结果表明,仿真结果与理论分析完全一致.     

基于六光子量子避错码的量子密钥分发方案

量子信道中不可避免存在的噪声将扭曲被传输的信息,对通信造成危害。目前克服量子信道噪声的较好方案是量子避错码（QEAC）。将量子避错码思想用于量子密钥分发,能有效克服信道中的噪声,且无需复杂的系统。用六光子构造了量子避错码,提出了一种丛于六光子避错码的量子密钥分发（QDK）方案。以提高量子密钥分发的量子比特效率和安全性为前提,对六光子避错码的所有可能态进行组合,得到一种六光子避错码的最优组合方法,可将两比特信息编码在一个态中,根据测肇结果和分组信息进行解码,得到正确信息的平均概率为7／16。与最近的基于四光子避错码的克服量子信道噪声的量子密钥分发方案相比,该方案的量子比特效率提高了16．67％,密钥分发安全性足它的3．5倍。     

New Quantum Key Distribution Scheme Based on Random Hybrid Quantum Channel with EPR Pairs and GHZ States

A theoretical quantum key distribution scheme based on random hybrid quantum channel with EPR pairs and GHZ states is devised. In this scheme, EPR pairs and tripartite GHZ states are exploited to set up random hybrid quantum channel. Only one photon in each entangled state is necessary to run forth and back in the channel. The security of the quantum key distribution scheme is guaranteed by more than one round of eavesdropping check procedures. It is of high capacity since one particle could carry more than two bits of information via quantum dense coding.     

Quantum Key Distribution Based on Coherent States

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预报单光子源诱骗态量子密钥产生率及数值计算

独立推导预报单光子源诱骗态量子密钥分发的密钥产生率计算公式,讨论密钥产生率和发送端探测效率的关系;进行弱相干光和预报单光子源诱骗态量子密钥分发的最优强度估计和密钥产生率数值计算.结果表明,预报单光子源诱骗态量子密钥分发的密钥产生率随着发送端探测效率的增加而增加,其安全通信距离与完美单光子源的通信距离一致;诱骗态量子密钥分发可提高安全通信距离和密钥产生率;预报单光子源由于减少了暗计数的影响,进一步提高了安全通信距离.     

Polarization Encoded Quantum Key Distribution over Special Optical Fibres

Employing a polarization compensator, an optical fibre quantum key distribution （QKD） system based on polarization coding has been developed. To obtain the compensator setting parameters, the measurement of the laser pulse polarization is performed with one single photon detector. We obtain a sifted key bit rate of about 2kbits/s and a qubit error rate lower than 10% within 3.5h. It is shown that polarization coding can be used for QKD over optical fibres as well. At the same time, the system is simple, easy to operate, practical and user-friendly. It gains more advantages than other systems over optical fibres when used in local area quantum communications and where the functional agility is important.     

Decoy State Quantum Key Distribution via Beam-Wandering Modeled Atmosphere Channel

We investigate the decoy state quantum key distribution via the atmosphere channels.We consider the efficient decoy state method with one-signal state and two-decoy states.Our results show that the decoy state method works even in the channels with fluctuating transmittance.Nevertheless,the key generation rate will be dramatically decreased by atmosphere turbulence,which sheds more light on the characterization of atmosphere turbulence in realistic free-space based quantum key distributions.     

Side Channel Passive Quantum Key Distribution with One Uninformative State

In most of quantum key distribution schemes, real random number generators are required on both sides for preparation and measurement bases choice. In this paper, via entangled photon pairs, we present a side channel passive quantum key distribution scheme, in which random number generator is unneeded on the receiver side. On the sender Alice side, along with massive of signal photons, small amount of uninformative photons are randomly sent to her partner Bob for eavesdropper-presence testing and error estimation. While on the other side channel, without using random number generator Bob do not actively measure the income signals randomly in two non-orthogonal bases. Instead, he just passively register photon click events, in two settled symmetric (i.e.X) bases, and the raw key(click events) is the probable outcomes of a special quantum measurement module constructed by Alice and Bob. Further, security analysis and formulas of security bounds for this scheme is also investigated under reasonable assumptions. Our work shows that the uninformative state employed in this paper is powerful to fight against eavesdropper Eve.     

光纤耦合对量子密钥分配系统光子探测的影响

借助量子密码术和卫星可以实现全球性的保密通信网络。但使用现有的单光子探测模块搭建星地量子密钥分配(QKD)系统,接收端就面临着空间光-多模光纤耦合的技术挑战。空间光-多模光纤耦合条件对星地量子密钥分配系统的跟瞄精度提出了严格要求。理论分析和定量计算表明,跟瞄精度ε与光束发散角θdiv的比值ε/dθiv≤0.5时,星地量子密钥分配系统的光子探测概率较高,系统可以正常工作;ε/dθiv≤0.1时,系统处于量子密钥产生速率为几kb/s的更理想状况。采用短波长更有利于满足空间光-多模光纤耦合条件,同时有利于系统获得更高的密钥产生速率。     

对称噪声信道下利用多纠缠态实现量子密钥分配

研究了对称噪声信道下的量子密钥分配(Quantum Key Distribution,QKD)过程,并得到了其误码率和信道保真度的关系式。基于量子态的局域区分原理,我们提出了使用“多纠缠态”进行噪声信道下的密钥分配的新方案。应用这个新方案,我们可以获得和在理想无噪声信道下使用最大纠缠态(四个Bell态之一)进行QKD一样好的结果。     

Tomography of Optical Single-Qubit Quantum Memory

JETP Letters - The mechanism of condensation of electron–hole pairs in the phase space in a highly degenerate semiconductor involving resonant photons of the electromagnetic field is...     

Multi-party Measurement-Device-Independent Quantum Key Distribution Based on Cluster States

We propose a novel multi-party measurement-device-independent quantum key distribution (MDI-QKD) protocol based on cluster states. A four-photon analyzer which can distinguish all the 16 cluster states serves as the measurement device for four-party MDI-QKD. Any two out of four participants can build secure keys after the analyzers obtains successful outputs and the two participants perform post-processing. We derive a security analysis for the protocol, and analyze the key rates under different values of polarization misalignment. The results show that four-party MDI-QKD is feasible over 280 km in the optical fiber channel when the key rate is about 10^??6 with the polarization misalignment parameter 0.015. Moreover, our work takes an important step toward a quantum communication network.     

Quantum Key Distribution Network Based on Differential Phase Shift

Using a series of quantum correlated photon pairs, we propose a theoretical scheme for any-to-any multi-user quantum key distribution network based on differential phase shift. The differential phase shift and the different detection time slots ensure the security of our scheme against eavesdropping. We discuss the security under the intercept-resend attack and the source replacement attack.     

Error Rate Estimation in Quantum Key Distribution with Finite Resources

The goal of quantum key distribution(QKD) is to generate secret key shared between two distant players,Alice and Bob. We present the connection between sampling rate and erroneous judgment probability when estimating error rate with random sampling method, and propose a method to compute optimal sampling rate, which can maximize final secure key generation rate. These results can be applied to choose the optimal sampling rate and improve the performance of QKD system with finite resources.     

Finite-Key Analysis for a Practical High-Dimensional Quantum Key Distribution System Based on Time-Phase States

High-dimensional quantum states key distribution(HD-QKD) can enable more than one bit per photon and tolerate more noise. Recently, a practical HD-QKD system based on time-phase states has provided a secret key at Mbps over metropolitan distances. For the purposes of further improving the secret key rate of a practical HD-QKD system, we make two main contributions in this work. Firstly, we present an improved parameter estimation for this system in the finite-key scenario based on the Chernoff bound and the improved Chernoff bound. Secondly, we analyze how the dimension d affects the performance of the practical HD-QKD system.We present numerical simulations about the secret key rate of the practical HD-QKD system based on different parameter estimation methods. It is found that using the improved Chernoff bound can improve the secret key rate and maximum channel loss of the practical HD-QKD system. In addition, a mixture of the 4-level and 8-level practical HD-QKD system can provide better performance in terms of the key generation rate over metropolitan distances.     

空间量子密码通信

量子密码术是一门崛起的新兴技术,其传输的安全性基于量子力学的Heisenberg不确定原理。而其中空间量子密码通信以其近期迅猛的发展和广阔的前景备受瞩目。本文从量子密码术的基本原理出发,综合叙述了空间量子密码通信的发展和最新成果。