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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. information and {4., and department of Physics, tsinghua university, beijing 100084. China key laboratory for Atomic and Molecular NanoSciences, tsinghua university, beijing 100084. China) key laboratory for {2. information and {4. Department of Physics Tsinghua University Bejjing 100084 China key laboratory for Atomic and Molecular NanoSciences Tsinghua University Bejing 100084 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.

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 {14. 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 {2. information and {4. 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

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 {4. 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.

Absence of State Collapse and Revival in a Superconducting Charge Qubit

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Communications in Theoretical Physics 2007年第12期48卷 1029-1032页

作者： HUO Wen-Yi~1 and LONG Gui-Lu~(1,2.3)~1 department of Physics amd key {2. for {4. information and measurements,tsinghua university,beijing100084.China~2.key {2. for Atomic and Molecular Nanosciences,tsinghua university,beijing 100084.China~3 National {2. for information Science and Technology,Hsinghua university,beijing 100084.China department of Physics amd key {2. for quantum {4. and measurements Tsinghua University Beijing 100084 China key laboratory for Atomic and Molecular Nanosciences Tsinghua University Beijing 100084 China National laboratory for information Science and Technology Hsinghua University Beijing 100084 China

The Hamiltonian of a superconducting charge qubit with a configuration of dc SQUID contains an interac-tion between the LC oscillator part and charge *** interaction may leads to quantum state collapse and revivalwhich degrades the charge qubits and leads to serious *** analysis shows that the existing charge qubitparameters do not lead to this phenomenon,which is very good for the superconducting charge

关键词： quantum computer superconducting charge qubit absence and revival

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. {4. 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 key laboratory For {2. information and {4. Department of Physics 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 key laboratory for Atomic and Molecular Nanosciences Tsinghua University Beijing 100084 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 {4. 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

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. 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.

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. information and {4., 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, beijing Normal university, beijing 100875, China beijing Radiation Center, beijing 100875, China key laboratory for Atomic and Molecular Nano-Sciences, tsinghua university, beijing 100084. China) key laboratory for {2. information and {4. Department of Physics Tsinghua University Beijing 100084 China key laboratory of Beam Technology and Material Modification Beijing Normal University Beijing 100875 China Institute of Low Energy Nuclear Physics Department of Material Science and Engineering Beijing Normal University Beijing 100875 China beijing Radiation Center Beijing 100875 China key laboratory for Atomic and Molecular Nano-Sciences Tsinghua University Beijing 100084 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.

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 {2. information and {4., department of Physics, tsinghua university, beijing 100084. China Center for {2. information, 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 key laboratory for {2. information and {4. Department of Physics Tsinghua University Beijing 100084 China Center for quantum information Tsinghua University Beijing 100084 China department of Materials Science and Engineering Beijing 100875 China Testing and Analytical Center Beijing Normal University Beijing 100875 China department of Physics Beijing Normal University Beijing 100875 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.

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. of Physics,{4., beijing 100084. China 2.6} National laboratory for information Science and Technology, beijing 100084. China key laboratory for Atomic and Molecular NanoSciences and {2. of Physics Tsinghua University Beijing China tsinghua National laboratory for {2. Science and Technology Beijing 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