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A scheme to implement the Deutsch-Josza algorithm on a superconducting charge-qubit quantum computer

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Progress in Natural Science:Materials International 2006年第6期16卷 594-599页

作者： HUO Wenyi and LONG Guilu (key laboratory for {2. {2. and measurements, and department of physics, tsinghua university, beijing 100084, China key laboratory for Atomic and Molecular NanoSciences, tsinghua university, beijing 100084, China) [a]key laboratory for {2. {2. and measurements and Department of Physics Tsinghua University Bejjing China [b]key laboratory for Atomic and Molecular NanoSciences Tsinghua University Bejing China

We have studied the implementation of the Deutsch-Josza quantum algorithm in a superconducting charge-qubit quantum computer. Different from previous studies, we have used the inductance coupled system of You et al. The detailed pulse sequences have been designed for the four possible functions in a 2.qubit system. The result is generalized to an arbitrary n-qubit system. This scheme will be useful for practical implementation of the algorithm.

关键词： superconducting quantum computer Deutsch-Josza algorithm.

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 {2. for {2. 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 100084 China Atomic and Molecular NanoSciences Tsinghua University Beijing 100084 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 02.001, 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 11602., 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 024001 China key laboratory for {2. {2. measurements Department of Physics Tsinghua University Beijing 100084 China department of physics Liaoning Normal University Dalian 116029 China key laboratory for Atomic Molecular Nano-Sciences Tsinghua University Beijing 100084 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

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{2.,{2., 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, {12. university of Posts and Telecommunications, {12. 100876, China) key laboratory for Atomic and Molecular NanoSciences and 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.

Dense coding scheme using superpositions of Bell-states and its NMR implementation

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Science China(physics,Mechanics & Astronomy) 2005年第1期48卷 57-67页

作者： ZHANG Jingfu, XIE Jingyi, DENG Zhiwei & LU Zhiheng key laboratory for quantum {2. and measurements, department of physics, tsinghua university, beijing 100084, China Center for quantum {2., tsinghua university, beijing 100084, China department of Materials Science and Engineering, beijing Normal university, beijing 100875, China Testing and Analytical Center, beijing Normal university, beijing 100875, China department of physics, beijing Normal university, beijing 100875, China 1. key laboratory for {2. {2. and measurements Department of Physics Tsinghua University 100084 Beijing China 2. Center for quantum information Tsinghua University 100084 Beijing China 3. department of Materials Science and Engineering Beijing Normal University 100875 Beijing China 4. Testing and Analytical Center Beijing Normal University 100875 Beijing China 5. department of physics Beijing Normal University 100875 Beijing China

Dense coding using superpositions of Bell-states is proposed. The generalized Grover's algorithm is used to prepare the initial entangled states, and the reverse process of the quantum algorithm is used to determine the entangled state in the decoding measurement. Compared with the previous schemes, the superpositions of two Bell-states are exploited. Our scheme is demonstrated using a nuclear magnetic resonance (NMR)quantum computer. The corresponding manipulations are obtained. Experimental results show a good agreement between theory and experiment. We also generalize the scheme to transmit eight messages by introducing an additional two-state system.

关键词： dense coding, superpositions of Bell-states, generalized Grover's algorithm, nuclear magnetic res-onance, quantum computer.

Multiparty quantum secret sharing of classical and quantum messages

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Progress in Natural Science:Materials International 2007年第1期17卷 26-31页

作者： CHEN Pan, DENG Fuguo and LONG Guilu ( key laboratory for {2. {2. and measurements, and department of physics, tsinghua university, beijing 100084, China key laboratory of Beam Technology and Material Modification, MOE, Institute of Low Energy Nuclear physics, and department of Material Science and Engineering, {12. Normal university, {12. 100875, China {12. Radiation Center, {12. 100875, China key laboratory for Atomic and Molecular Nano-Sciences, tsinghua university, beijing 100084, China) [a]key laboratory for {2. {2. and measurements and Department of Physics Tsinghua University Beijing China [b]key laboratory of Beam Technology and Material Modification MOE Institute of Low Energy Nuclear Physics and Department of Material Science and Engineering Beijing Normal University Beijing China [c]beijing Radiation Center Beijing China [d]key laboratory for Atomic and Molecular Nano-Sciences Tsinghua University Beijing China

A scheme for multiparty quantum secret sharing of classical and quantum messages is proposed by using entanglement swapping. This scheme can distribute not only the classical {2. but also the quantum informati... 详细信息

关键词： quantum secret sharing classical message quantum message EPR pair.

Implementation of a multiple round quantum dense coding using nuclear magnetic resonance

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Science China(physics,Mechanics & Astronomy) 2005年第6期48卷 706-715页

作者： ZHANG Jingfu1, XIE Jingyi2. WANG Chuan1, DENG Zhiwei3, LU Zhiheng4, & LONG Guilu1,5 1. key laboratory For {2. {2. and measurements of MOE, department of physics, tsinghua university, beijing 100084,China 2. department of Materials Science and Engineering, beijing Normal university, beijing 100875, China 3. Testing and Analytical Center, beijing Normal university, beijing 100875,China 4. department of physics, beijing Normal university, beijing 100875, China 5. key laboratory For atomic and Molecular Nanosciences, tsinghua university, beijing 100084,China 1. key laboratory For {2. {2. and measurements of MOE Department of Physics Tsinghua University 100084 Beijing China 2. department of Materials science and Engineering Beijing Normal University 100875 Beijing China 3. Testing and Analytical Center Beijing Normal University 100875 Beijing China 4. department of physics Beijing Normal University 100875 Beijing China 5. key laboratory For Atomic and Molecular Nanosciences Tsinghua University 100084 Beijing China

A multiple round quantum dense coding scheme based on the quantum phase estimation algorithm is proposed and implemented in a three qubit nuclear magnetic resonance (NMR) quantum computer. Using an m + 1 qubit system, Bob can transmit one of 2.+1 messages to Alice, through manipulating only one qubit and exchanging it between Alice and Bob for m rounds. The information capacity is enhanced to m + 1 bits as compared to m bits in a classical scheme. The scheme has been demonstrated in NMR system, and the experimental results show a good agreement between theory and experiment.

关键词： quantum dense coding, multiple round, nuclear magnetic resorance

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{2.,{2., beijing 100084, China 2.5} National laboratory for information Science and Technology, beijing 100084, China 1. key laboratory for Atomic and Molecular NanoSciences and{2. Tsinghua University Beijing 100084 China2. Tsinghua National Laboratory for Information Science and Technology Beijing 100084 China

A detailed analysis has showed that the quantum secret sharing protocol based on the Grover algorithm (Phys Rev A, 2.03, 68: 02.306) 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

Suppression of Phase and Amplitude Damping Decoherence in a Three-Level Atom in A-Configuration Using Bang-Bang Controls

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Communications in Theoretical physics 2007年第7期48卷 71-74页

作者： WANG Yan-Hui LIU Xiao-Shu LONG Gui-Lu1 key laboratory for Atomic and Molecular NanoSciences and{2.,{2. university,beijing 100084,China2.{2. National laboratory for information Science and Technology,{2. university,beijing 100084,China key laboratory for Atomic and Molecular NanoSciences and{2. Tsinghua University Beijing 100084 China tsinghua National laboratory for {2. Science and Technology Tsinghua University Beijing 100084 China

In this paper,we present decoupling bang-bang operations for the suppression of general decoherence,bothamplitude and phase damping,in a three-level system in *** give a program to design a sequence ofperiodic twinbor... 详细信息

关键词： bang-bang operation general decoherence three-level system