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Measuring-basis-encrypted six-state quantum key distribution scheme

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Progress in Natural Science:Materials International 2006年第1期16卷 84-89页

作者： CHEN Pan1, DENG Fuguo1, WANG Pingxiao1 and long guilu1,2 (Key Laboratory for Quantum Information and Measurements and department of physics, tsinghua university, beijing 100084, china 2. Key Laboratory for Atomic and Molecular NanoSciences, tsinghua university, beijing 100084, china) Key Laboratory for Quantum Information and Measurements Department of Physics Tsinghua University Beijing 100084 China Key Laboratory for Atomic and Molecular NanoSciences Tsinghua University Beijing 100084 China

A six-state quantum key distribution scheme with measuring-basis encryption technique, which is based on the six-state protocol and the MBE protocol, is proposed. In this modified six-state quantum key distribution protocol, Alice and Bob use a control key to synchronize the use of their measuring-basis so that they always use the same measuring-basis. This modified six-state quantum key distribution protocol retains the advantage of higher security and at the same time has a higher efficiency.

关键词： quantum key distribution measuring-basis encrypted six-state security.

Eavesdropping in a quantum secret sharing protocol based on Grover algorithm and its solution

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Science china(physics,Mechanics & Astronomy) 2010年第3期53卷 491-495页

作者： HAO liang1, li Junlin1 & long guilu1,2.1Key Laboratory for Atomic and Molecular NanoSciences and department of physics, tsinghua university, beijing 100084, china 2tsinghua National Laboratory for Information Science and Technology, beijing 100084, china Key Laboratory for Atomic and Molecular NanoSciences and department of physics Tsinghua University Beijing China tsinghua National Laboratory for Information Science and Technology Beijing China

A detailed analysis has showed that the quantum secret sharing protocol based on the Grover algorithm (Phys Rev A, 2003, 68: 022306) is insecure. A dishonest receiver may obtain the full information without being detected. A quantum secret-sharing protocol is presents here, which mends the security loophole of the original secret-sharing protocol, and doubles the information capacity.

关键词： quantum secret sharing Grover algorithm quantum cryptography quantum search algorithm

Two mode photon bunching effect as witness of quantum criticality in circuit QED

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Science china(physics,Mechanics & Astronomy) 2009年第12期52卷 1898-1905页

作者： AI Qing1,WANG YingDan2,long guilu1,3 & SUN ChangPu4 1 department of physics,tsinghua university,beijing 100084,china 2 department of physics,university of Basel,Klingelbergstrasse 82,4056 Basel,Switzerland 3 tsinghua National Laboratory for Information Science and Technology,beijing 100084,china 4 Institute of Theoretical physics,Chinese Academy of Sciences,beijing 100080,china department of physics Tsinghua University Beijing China department of physics University of Basel Basel Switzerland tsinghua National Laboratory for Information Science and Technology Beijing China Institute of Theoretical physics Chinese Academy of Sciences Beijing China

We suggest a scheme to probe critical phenomena at a quantum phase transition (QPT) using the quantum correlation of two photonic modes simultaneously coupled to a critical system. As an experimentally accessible physical implementation,a circuit QED system is formed by a capacitively coupled Josephson junction qubit array interacting with one superconducting transmission line resonator (TLR). It realizes an Ising chain in the transverse field (ICTF) which interacts with the two magnetic modes propagating in the TLR. We demonstrate that in the vicinity of criticality the originally independent fields tend to display photon bunching effects due to their interaction with the ICTF. Thus,the occurrence of the QPT is reflected by the quantum characteristics of the photonic fields.

关键词： quantum phase transition photon bunching circuit QED

MULTISTEP DISCRETIZATION OF INDEX 3 DAES

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Journal of Computational Mathematics 2000年第3期18卷 325-336页

作者： Yang Cao Qing-yang li (department of Mathematics, tsinghua university, beijing 100084, china) 清华大学北京 100084

Studies the different types of multistep discretization of index 3 differential-algebraic equations in Hessenberg form. Existense, uniqueness and influence of perturbations; Local convergence of multistep discretizati... 详细信息

关键词： multistep methods Adams method BDF DAEs Index 3

Arbitrarily long distance quantum communication using inspection and power insertion

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Chinese Science Bulletin 2009年第1期54卷 158-162页

作者： WANG WanYing1,2,WANG Chuan1,2,ZHANG GuangYu1,3 & long guilu1,2.1 department of physics,tsinghua university,beijing 100084,china 2 tsinghua National Laboratory for Information Science and Technology,tsinghua university,beijing 100084,china 3 College of Applied Science,Harbin university of Science and Technology,Harbin 150080,china department of physics Tsinghua University Beijing China tsinghua National Laboratory for Information Science and Technology Tsinghua University Beijing China College of Applied Science Harbin University of Science and Technology Beijing China

The biggest obstacle for long distance quantum communication is the channel loss and the channel noise on photons. In this paper,a method to solve this problem was analyzed using inspection and power insertion (IPI). It is proved that quantum communication may be established over arbitrarily long distance using this technology. The amount of resources required is a polynomial function of the dis-tance. IPI is proposed as a general technique to prolong quantum secure direct communication where secret messages are transmitted directly over a quantum channel.

关键词：长距离量子通信量子安全通信量子密匙分布噪声

Influence of magnetic current on the ground state entanglement in an isotropic transverse XY chain

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Progress in Natural Science:Materials International 2007年第10期17卷 1147-1151页

作者： liu Dan1,2 , Zhang Yong3 and long guilu1,2.1. Key Laboratory for Atomic and Molecular NanoSciences, and department of physics, tsinghua university, beijing 100084, china 2. Center of Quantum Information Science and Technology, tsinghua National Laboratory for information Science and Technology, beijing 100084, china 3. Institute of physics, School of Sciences, beijing university of Posts and Telecommunications, beijing 100876, china) Key Laboratory for Atomic and Molecular NanoSciences Department of Physics Tsinghua University Beijing 100084 China Center of Quantum Information Science and Technology Tsinghua National Laboratory for Information Science and Technology Beijing 100084 China Institute of physics School of Sciences Beijing University of Posts and Telecommunications Beijing 100876 China

We study the ground state entanglement in a three-qubit XY chain under the influence of a magnetization current. It is found that the ground state changes from a W state to a disentangled state as the magnetic field varies. When the Lagrange multiplier λ>3, namely under a strong magnetic current, the ground state holds onto a W state for a large range of the magnetic field strength. A phase transition to the magnetization-current phase occurs under a certain condition.

关键词： Heisenberg-XY chain magnetic-current phase transition.

Experimental realization of quantum cryptography communication in free space

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Science china(physics,Mechanics & Astronomy) 2005年第2期48卷 237-246页

作者： WANG Chuan1, ZHANG Jingfu1, WANG Pingxiao1, DENG Fuguo1, AI Qing1 & long guilu1,2.1. department of physics, Key Laboratory for Quantum Information and Measurements, tsinghua Univer- sity, beijing 100084, china 2. Center for Atomic and Molecular NanoSciences, tsinghua university, beijing 100084, china department of physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing China Atomic and Molecular NanoSciences Tsinghua University Beijing China

Utilizing linear optical devices, the principle of B92 quantum key distribution (QKD) protocol is demonstrated in free space with a distance of transmission of 2.2 meters. The faint laser pulses with 650 nm wavelength are used as the single photon sources. The experimental results show that the eavesdropping behavior in the signal transmission can be detected. We also discuss the problems and solutions in using the quantum cryptography communication practically. It is pointed out that one of the approaches to increasing the distance of the quantum communication is to overcome the attenuation of the single photon in transmission. This could not be solved by the use of single photon source, and new quantum communication protocols are needed to solve these problems.

关键词： quantum key distribution, free space, linear optics, faint pulses.

Entropy product measure for multipartite pure states

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Science china(physics,Mechanics & Astronomy) 2006年第5期49卷 606-615页

作者： CAO Wancang1,2, liU Dan2, PAN Feng3 & long guilu2,4 1. department of physics, Chifeng College, Chifeng 024001, china 2. Key Laboratory for Quantum Information and Measurements, department of physics, tsinghua university, beijing 100084, china 3. department of physics, liaoning Normal university, Dalian 116029, china 4. Key Laboratory for Atomic and Molecular Nano-Sciences, tsinghua university, beijing 100084, china Correspondence should be addressed to long guilu department of physics Chifeng College Chifeng China Key Laboratory for Quantum Information and Measurements Department of Physics Tsinghua University Beijing China department of physics Liaoning Normal University Dalian China Key Laboratory for Atomic and Molecular Nano-Sciences Tsinghua University Beijing China

An entanglement measure for multipartite pure states is formulated using the product of the von Neumann entropy of the reduced density matrices of the constituents. Based on this new measure, all possible ways of the maximal entanglement of the triqubit pure states are studied in detail and all types of the maximal entanglement have been compared with the result of ‘the average entropy’. The new measure can be used to calculate the degree of entanglement, and an improvement is given in the area near the zero entropy.

关键词： multipartite pure state von Neumann entropy entanglement measure

An N/4 fixed-point duality quantum search algorithm

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中国科学：物理学、力学、天文学英文版 2010年第9期53卷 1765-1768页

作者： HAO liang1,liU Dan2.& long guilu1,3 1Key Laboratory for Atomic and Molecular NanoSciences and department of physics,tsinghua university,beijing 100084,china 2School of Sciences,Dalian Nationalities university,Dalian 116600,china 3tsinghua National Laboratory for Information Science and Technology,beijing 100084,china Key Laboratory for Atomic and Molecular NanoSciences and department of physics Tsinghua University Beijing China School of Sciences Dalian Nationalities University Dalian China tsinghua National Laboratory for Information Science and Technology Beijing China

Here a fixed-point duality quantum search algorithm is *** algorithm uses iteratively non-unitary operations and measurements to search an unsorted *** the marked item is found,the algorithm stops *** algorithm uses a constant non-unitary operator,and requires N/4 steps on average(N is the number of data from the database) to locate the marked *** implementation of this algorithm in a usual quantum computer is also demonstrated.

关键词： fixed-point search algorithm duality quantum computing the N4 duality search algorithm