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在星舰量子密钥分发系统中,发送量子密钥的量子卫星是低轨道卫星,追踪量子卫星的接收设备安装在船舰上.接收设备需要追踪卫星的运动,接收端基矢不可避免地会发生旋转.分析了导致基矢旋转的原因,针对BB84协议,建立了基矢旋转角与量子误码率、获取信息量的定量关系.结果表明,当传输距离为200 km,基矢旋转角分别为2°和10°时... 相似文献
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一种基于迈克耳逊干涉仪的单向量子密钥分发系统,采用法拉第旋转镜和四端口偏振分束器的组合,消除了光纤及光学器件的双折射效应,具有自稳定特性.信息编码在光子的相位上,通过检测光子的偏振进而解码出信息.以中心波长1310 nm的单光子脉冲,在50 km的干线光纤中获得了30 dB的消光比. 相似文献
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在以单模光纤作为量子信道,并采用光子偏振编码方式的量子密钥分发过程中,光纤的双折射效应会导致光子在光纤中传播时其偏振态发生随机变化,使安全密钥的最终成码率大幅度降低.利用两个四分之一波片和一个半波片的组合作为校正器,可以实现对任意偏振态的校正补偿.建立了一种以该类偏振校正器为执行机构的基于随机并行梯度下降控制算法的实时偏振补偿仿真控制模型,讨论了算法的随机扰动幅度、增益系数与收敛速度的关系,分析了算法对于偏振的校准能力.通过实验对算法的性能进行了验证.实验结果表明,经过一定次数的迭代后可将系统的偏振消光比校正到一个比较理想的状态. 相似文献
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提出了一种基于W态的量子确定性密钥分发方案,方案采用在量子信道中传输更加稳定的W态作为承载信息的粒子,利用量子相干特性以及一串公开的信息序列S作为密钥分发的关键,在兼顾传输粒子稳定性的前提下能够达到54.54%的密钥分发效率,与使用GHZ态相比,在效率相差无几的情况下保证粒子在传输过程中具有更强的鲁棒性。安全分析表明,此方案能经受窃听者采取的截获——转发(重发)攻击和纠缠攻击两种攻击方式,确保通信安全可靠。同时,该方案在执行过程中不涉及任何幺正操作,简单便捷。 相似文献
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提出一个基于单光子偏振的量子密钥分配方案.在这个方案里, Alice首先制备一串任意单光子态,然后发送给Bob.Bob只需对其进行一个U操作,再发回Alice.最后Alice对单光子态进行测量,即可实现量子密钥分配.此方案需要一个无噪声信道,优点在于仅仅需要单光子态,以及局域操作和单光子偏振态的测量,这些都非常易于实现.最后其安全性也是有理论保证的. 相似文献
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为了提高确定性密钥分发效率,提出了基于GHZ态纠缠交换的量子确定性密钥分发(Quantum deterministic key distribution,QDKD)方案,方案充分利用量子力学纠缠交换的原理,通信双方通过共享一对GHZ粒子态,在纠缠、测量操作后接收者Bob可根据发送者Alice发送的经典信息推断出确定密钥,该协议与其他基于GHZ纠缠态的QDKD方案不同之处在于,使用的两个GHZ粒子态制备操作且粒子分发操作由Bob完成,安全分析表明窃听者的窃听行为会被及时发现。所提出的方案是高效的,除去用于窃听检测的粒子,所剩的粒子全部用于信息传输,能够达到60%的密钥分发效率,且方案可操作性强. 相似文献
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Based on the comparison between ontology and thesaurus, and the analysis of an ontology-based Information Retrieval (IR) model, the potential advantages that ontology may contribute to IR are analyzed. Then a general architecture of ontology-based Information Retrieval System (IRS) and the approach of constructing it are presented. Based on the researches, the role of ontology in IR is summarized from four aspects and a typical system called Textpresso is analyzed. Finally, a conclusion is drawn that utilizing ontology is the trend of IR and can really improve the IRS. 相似文献
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Eli Biham Michel Boyer P. Oscar Boykin Tal Mor Vwani Roychowdhury 《Journal of Cryptology》2006,19(4):381-439
We prove the security of theoretical quantum key distribution against the most general attacks which can be performed on the
channel, by an eavesdropper who has unlimited computation abilities, and the full power allowed by the rules of classical
and quantum physics. A key created that way can then be used to transmit secure messages such that their security is also
unaffected in the future. 相似文献
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一种基于量子纠错编码的量子密钥分配协议 总被引:3,自引:0,他引:3
量子加密从物理机制上保证了密钥分配的绝对安全,然而由于量子密钥分配过程中量子信道存在噪声,使得传输效率不高的量子密钥分配效率进一步降低。量子低密度奇偶校验(量子LDPC)码由于在码长和码率的选择方面具有巨大的灵活性,且信赖于稀疏图,已成为目前量子纠错编码的研究热点。该文借鉴经典纠错编码能够提高传输可靠性的特性,针对BB84协议,设计一种基于量子LDPC码的BB84协议。通过数值仿真,分析量子LDPC码对BB84协议的密钥传输效率的影响。结果表明基于量子纠错码的BB84协议的密钥传输效率得到提高,验证了在含噪量子信道中基于量子LDPC码的量子密钥分配协议的有效性。 相似文献
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研究了信息检索结果多样化的方法。首先实现了经典的检索结果重排序最大边缘相关(MMR)算法,进而设计了三种基于查询日志的子查询构造方法:单字向后扩展,双字向后扩展和双向子串扩展,并最终探讨了将这三种子查询构造方法分别与最大边缘相关算法相结合的使用策略。实验表明,采用上述方法实现的系统能明显提高信息检索结果的多样性。 相似文献
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A private information retrieval scheme allows a user to retrieve a data item of his choice from a remote database (or several copies of a database) while
hiding from the database owner which particular data item he is interested in. We consider the question of private information
retrieval in the so-called ``commodity-based' model, recently proposed by Beaver for practically oriented service-provider
Internet applications. We present simple and modular schemes allowing us to reduce dramatically the overall communication
involving users, and substantially reduce their computation, using off-line messages sent from service-providers to databases
and users. The service-providers do not need to know the database contents nor the future user's requests; all they need to
know is an upper bound on the data size. Our solutions can be made resilient against collusions of databases with more than
a majority (in fact, all-but-one) of the service-providers.
Received 21 September 1998 and revised 21 December 1999 Online publication 19 May 2000 相似文献
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Qi Haoliang Li Sheng Gao Jianfeng Han Zhongyuan Xia Xinsong 《电子科学学刊(英文版)》2008,25(1):120-124
This letter presents a new discriminative model for Information Retrieval (IR), referred to as Ordinal Regression Model (ORM). ORM is different from most existing models in that it views IR as ordinal regression problem (i.e. ranking problem) instead of binary classification. It is noted that the task of IR is to rank documents according to the user information needed, so IR can be viewed as ordinal regression problem. Two parameter learning algorithms for ORM are presented. One is a perceptron-based algorithm. The other is the ranking Support Vector Machine (SVM). The effectiveness of the proposed approach has been evaluated on the task of ad hoc retrieval using three English Text REtrieval Conference (TREC) sets and two Chinese TREC sets. Results show that ORM significantly outperforms the state-of-the-art language model approaches and OKAPI system in all test sets; and it is more appropriate to view IR as ordinal regression other than binary classification. 相似文献
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为解决量子信令在远距离传输过程中的纯化中继问题,提出了基于两级偏振分光镜的纠缠纯化方案。采用三个偏振分光镜构建方案,第一级含一个偏振分光镜,第二级有两个偏振分光镜,让混合态的量子信令纠缠态通过两级偏振分光镜后,会产生一对新的纠缠态,继而用新的纠缠态来替代原来的混合态,最终实现纯化的目的。对每一种输入态进行分析验证,结果表明,所提出的纠缠纯化方案可以有效的实现量子信令的纯化,具有很好的应用性和操作性。该方案的研究对未来量子通信中信令的传输具有一定的技术参考作用。 相似文献