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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 {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 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 02.001, china 2. Key {2. 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 {2. 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 {2. 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

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,{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 {12., 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.

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 quantum {2. and measurements, and department of physics, tsinghua university, Beijing 100084. china Key laboratory for Atomic and Molecular NanoSciences, tsinghua university, Beijing 100084. china) Key laboratory for quantum {2. and measurements 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.

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 laboratory for {2. information and measurements,tsinghua university,Beijing100084.china~2.Key laboratory for Atomic and Molecular Nanosciences,tsinghua university,Beijing 100084.china~3 National laboratory for information Science and Technology,Hsinghua university,Beijing 100084.china department of physics amd Key {2. for quantum information 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

Parameter estimation for whole-body kinetic model of FDG metabolism

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Progress in Natural Science:Materials International 2006年第11期16卷 1164-1170页

作者： CUI Yunfeng~1, BAI Jing~1**, CHEN Yingmao~2.and TIAN Jiahe~2.1. department of Biomedical Engineering, tsinghua university, Beijing {2. china 2. department of Nuclear Medicine, General Hospital of PLA, Beijing 100853, china) department of Biomedical Engineering Tsinghua University Beijing 100084 China department of Nuclear Medicine General Hospital of PLA Beijing 100853 China

Based on the radioactive tracer [ ~ 18 F]2.fluoro-2.deoxy-D-glucose （FDG）, positron emission tomography （PET）, and compartment model, the tracer kinetic study has become an important method to investigate the glucose metabolic kinetics in human body. In this work, the kinetic parameters of three-compartment and four-parameter model for the FDG metabolism in the tissues of myocardium, lung, liver, stomach, spleen, pancreas, and marrow were estimated through some dynamic FDG-PET experiments. Together with published brain and skeletal muscle parameters, a relatively complete whole-body model was presented. In the liver model, the dual blood supply from the hepatic artery and the portal vein to the liver was considered for parameter estimation, and the more accurate results were obtained using the dual-input rather than the single arterial-input. The established whole-body model provides the functional information of FDG metabolism in human body. It can be used to further investigate the glucose metabolism, and also be used for the simulation and visualization of FDG metabolic process in human body.

关键词： compartment model FDG PET parameter estimation.

Electric-stimulus rate encoding algorithm of Mandarin tonal information in cochlear implant

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Progress in Natural Science:Materials International 2006年第12期16卷 1315-1321页

作者： GUAN Tian~1, GONG Qin~1 and YE Datian~2.*(1. department of Biomedical Engineering, tsinghua university, Beijing {2. china 2. Research Center of Biomedical Engineering, Graduate School at Shenzhen, tsinghua university, Shenzhen 518055, china) department of Biomedical Engineering Tsinghua University Beijing 100084 China Research Center of Biomedical Engineering Graduate School Shenzhen Tsinghua University Shenzhen 518055 China

The modern multi-channel cochlear implants usually extract and encode the temporal envelope cues. This kind of algorithms can hardly satisfy the users who speak tonal languages, such as Mandarin. Many studies have tried to enhance the recognition ability of Mandarin through encoding tonal information and made suggestions to frequency-modulate the fixed pulse-rate carrier with the extracted tonal information based on the rate-pitch theory in electric hearing. However, how to encode and deliver the tonal information such as F_0by changing electric-stimulus rate has not got further study in clinical electric-stimulus mode. The present paper focuses on this matter by piecewise calculating the appreciable electric-stimulus rates. Then an electric-stimulus encoding algorithm of Mandarin tone is brought forward and testified through acoustic simulations. Such conclusion can be drawn that this algorithm of electric-stimulus rate could convey tonal information well and help to enhance the Mandarin speech recognition ability.

关键词： cochlear implant tone fundamental frequency electric-stimulus rate.

A user-space file system for on-demand legacy desktop software

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Science china(information Sciences) 2011年第6期54卷 1142-1150页

作者： ZHANG YouHui 1,2., SU GeLin 1,2.& ZHENG WeiMin 1,2.1 department of Computer Science and Technology, tsinghua university, Beijing {2. china 2.tsinghua National laboratory for information Science and Technology, tsinghua university, Beijing {2. china department of Computer Science and Technology Tsinghua University Beijing China tsinghua National laboratory for {2. Science and Technology Tsinghua University Beijing China

Some user-level virtualization technologies have been used to convert legacy software (like the existing Windows desktop applications) into the on-demand software without any modification. To give the client a friendly and compatible method to access on-demand legacy software across the Internet, this paper presents a clientend file system for this usage case. It is a Windows user-space file system based on the cloud storage (where the on-demand software is stored), which converts the local file system accesses into remote visits. Quite a few optimizations are adopted and adjusted to suit the file-access-pattern of on-demand software, including the local cache, metadata/data/software prefetch and content-addressable storage (CAS), to decrease the number of remote visits and/or to overlap IO (input/output) operations with software execution. Detailed access-pattern analyses are also presented. This file system has been implemented and tests show that it is practical for much daily-used software-a local cache of limited size can provide up to 80% hit ratio and the corresponding overhead of running-time is about 37%. Owing to this method, on any compatible and networked computer, a user can use his/her personalized software conveniently although it does not exist on the local host.

关键词： on-demand software software as a service user-space file system cloud storage

Calculation of maximum ground movement and deformation caused by mining

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中国有色金属学会会刊：英文版 2011年第S3期21卷 562-569页

作者： LI Pei-xian1, 2. TAN Zhi-xiang1, 2. DENG Ka-zhong1, 2.1. Key laboratory for Land Environment and Disaster Monitoring of State Bureau of Surveying and Mapping, china {2. of Mining and Technology, Xuzhou 2.1116, china 2. Jiangsu Key laboratory of Resources and Environmental information Engineering, china {2. of Mining and Technology, Xuzhou 2.1116, china Key laboratory for Land Environment and Disaster Monitoring of State Bureau of Surveying and Mapping China University of Mining and Technology Xuzhou 221116 China Jiangsu Key laboratory of Resources and Environmental information Engineering China University of Mining and Technology Xuzhou 221116 China

In order to know the maximum mining ground deformation of arbitrary surface point, directions of the maximum surface tilt, curvature,horizontal displacement and horizontal deformation caused by multi-working faces were deduced based on probability integral method. The distribution forms of surface deformations in all direction φ∈[0, 2.] were obtained and also equations of maximum deformations were given based on calculation of mining ground deformation in direction φ. A mining subsidence analysis system was developed with VB6.0. The system implements the probability integral mining subsidence prediction with direct integration method, and it can avoid errors of arbitrary shaped working face subdivision of traditional method, and accuracy of mining subsidence prediction can be improved with the direct integral method. The system implements the contour chart and profile chart and also data analysis automation by manipulation of the SURFER kernel function and it complements the defect of existing subsidence prediction software. Calculation of maximum deformations caused by multi-working faces mining in a coal mine of Xuzhou, china was shown as application example. Engineering application indicates that maximum deformation of mining ground surface can be calculated and analyzed by the system. The research provides a theoretical basis and calculation tool for mining subsidence prediction and analysis.

关键词： mining subsidence probability integral method movement and deformation system development