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  • Single atoms transferring between a magneto-optical trap and a far-off-resonance optical dipole trap

    He Jun, Wang Jing, Yang Bao-Dong, Zhang Tian-Cai, Wang Jun-Min
    Chin. Phys. B 2009, 18 (8): 3404-3408
    Based on our work on single cesium atoms trapped in a large-magnetic-gradient vapour-cell magneto-optical trap (MOT), the signal-to-noise ratio (SNR) is remarkably improved. Also a far-off-resonance optical dipole trap (FORT) formed by a strongly-focused 1064~nm single frequency Nd:YVO4 laser beam i...

     
  • Long-distance quantum teleportation assisted with free-space entanglement distribution

    Ren Ji-Gang, Yang Bin, Yi Zhen-Huan, Zhou Fei, Chen Kai, Peng Cheng-Zhi, Pan Jian-Wei
    Chin. Phys. B 2009, 18 (8): 3605-3610
    Faithful long-distance quantum teleportation necessitates prior entanglement distribution between two communicated locations. The particle carrying on the unknown quantum information is then combined with one particle of the entangled states for Bell-state measurements, which leads to a transfer of ...

     
Chin. Phys. B  
  Chin. Phys. B--2009, Vol.18, No.8
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GENERAL

A numerical method for one-dimensional nonlinear sine-Gordon equation using multiquadric quasi-interpolation

Ma Li-Min, Wu Zong-Min
Chin. Phys. B, 2009, 18 (8): 3099-3103 doi: 10.1088/1674-1056/18/8/001
Full Text: [PDF 172 KB] (Downloads:1161)
Show Abstract
In this paper, we use a univariate multiquadric quasi-interpolation scheme to solve the one-dimensional nonlinear sine-Gordon equation that is related to many physical phenomena. We obtain a numerical scheme by using the derivative of the quasi-interpolation to approximate the spatial derivative and a difference scheme to approximate the temporal derivative. The advantage of the obtained scheme is that the algorithm is very simple so that it is very easy to implement. The results of numerical experiments are presented and compared with analytical solutions to confirm the good accuracy of the presented scheme.

Automatic generation of min-weighted persistent formations

Luo Xiao-Yuan, Li Shao-Bao, Guan Xin-Ping
Chin. Phys. B, 2009, 18 (8): 3104-3114 doi: 10.1088/1674-1056/18/8/002
Full Text: [PDF 867 KB] (Downloads:759)
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This paper researched into some methods for generating min-weighted rigid graphs and min-weighted persistent graphs. Rigidity and persistence are currently used in various studies on coordination and control of autonomous multi-agent formations. To minimize the communication complexity of formations and reduce energy consumption, this paper introduces the rigidity matrix and presents three algorithms for generating min-weighted rigid and min-weighted persistent graphs. First, the existence of a min-weighted rigid graph is proved by using the rigidity matrix, and algorithm 1 is presented to generate the min-weighted rigid graphs. Second, the algorithm 2 based on the rigidity matrix is presented to direct the edges of min-weighted rigid graphs to generate min-weighted persistent graphs. Third, the formations with range constraints are considered, and algorithm 3 is presented to find whether a framework can form a min-weighted persistent formation. Finally, some simulations are given to show the efficiency of our research.

Some characteristics of three exact solutions of Einstein equations minimally coupled to a Quintessence field

Zhou Xiao-Hua
Chin. Phys. B, 2009, 18 (8): 3115-3121 doi: 10.1088/1674-1056/18/8/003
Full Text: [PDF 296 KB] (Downloads:614)
Show Abstract
We show some characteristics of three exact solutions to Einstein's gravity equation minimally coupled to a Quintessence field. Besides eternal inflation, several other interesting inflationary processes, such as transitory inflation, are obtained in these solutions. Singularity is avoided in some special cases.

Are networks with more edges easier to synchronize, or not?

Duan Zhi-Sheng, Wang Wen-Xu, Liu Chao, Chen Guan-Rong
Chin. Phys. B, 2009, 18 (8): 3122-3130 doi: 10.1088/1674-1056/18/8/004
Full Text: [PDF 272 KB] (Downloads:585)
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In this paper, the relationship between network synchronizability and the edge-addition of its associated graph is investigated. First, it is shown that adding one edge to a cycle definitely decreases the network synchronizability. Then, since sometimes the synchronizability can be enhanced by changing the network structure, the question of whether the networks with more edges are easier to synchronize is addressed. Based on a subgraph and complementary graph method, it is shown by examples that the answer is negative even if the network structure is arbitrarily optimized. This reveals that generally there are redundant edges in a network, which not only make no contributions to synchronization but actually may reduce the synchronizability. Moreover, a simple example shows that the node betweenness centrality is not always a good indicator for the network synchronizability. Finally, some more examples are presented to illustrate how the network synchronizability varies following the addition of edges, where all the examples show that the network synchronizability globally increases but locally fluctuates as the number of added edges increases.

A counterexample of the Euler condition: the Appell—Hamel dynamical system on a horizontally moving plate

Xu Shan-Shan, Li Shu-Min, Berakdar Jamal
Chin. Phys. B, 2009, 18 (8): 3131-3134 doi: 10.1088/1674-1056/18/8/005
Full Text: [PDF 251 KB] (Downloads:522)
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As a counterexample of the Euler condition for nonholonomic constraint problems [H. C. Shen, Acta Phys. Sin. 54, 2468 (2005)], we investigate the Apell--Hamel dynamical system on a horizontally moving plate. The inconsistency of the results with Newton mechanics suggests that the Euler condition is not a universal model for nonlinear nonholonomic systems. This is attributed to the fact that the virtual displacements so obtained are not normal to the constraint forces.

Hojman's theorem of the third-order ordinary differential equation

Lü Hong-Sheng, Zhang Hong-Bin, Gu Shu-Long
Chin. Phys. B, 2009, 18 (8): 3135-3138 doi: 10.1088/1674-1056/18/8/006
Full Text: [PDF 134 KB] (Downloads:756)
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This paper extends Hojman's conservation law to the third-order differential equation. A new conserved quantity is constructed based on the Lie group of transformation generators of the equations of motion. The generators contain variations of the time and generalized coordinates. Two independent non-trivial conserved quantities of the third-order ordinary differential equation are obtained. A simple example is presented to illustrate the applications of the results.

Conformal invariance and conserved quantities of dynamical system of relative motion

Chen Xiang-Wei, Zhao Yong-Hong, Li Yan-Min
Chin. Phys. B, 2009, 18 (8): 3139-3144 doi: 10.1088/1674-1056/18/8/007
Full Text: [PDF 160 KB] (Downloads:971)
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This paper discusses in detail the conformal invariance by infinitesimal transformations of a dynamical system of relative motion. The necessary and sufficient conditions of conformal invariance and Lie symmetry are given simultaneously by the action of infinitesimal transformations. Then it obtains the conserved quantities of conformal invariance by the infinitesimal transformations. Finally an example is given to illustrate the application of the results.

Symmetry of Lagrangians of holonomic systems in terms of quasi-coordinates

Wu Hui-Bin, Mei Feng-Xiang
Chin. Phys. B, 2009, 18 (8): 3145-3149 doi: 10.1088/1674-1056/18/8/008
Full Text: [PDF 143 KB] (Downloads:715)
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This paper discusses the symmetry of Lagrangians of holonomic systems in terms of quasi-coordinates. Firstly, the definition and the criterion of the symmetry are given. Secondly, the condition under which there exists a conserved quantity and the form of the conserved quantity are obtained. Finally, an example is shown to illustrate the application of the results.

A New type of conserved quantity deduced from Mei symmetry of nonholonomic systems in terms of quasi-coordinates

Pang Ting, Fang Jian-Hui, Zhang Ming-Jiang, Lin Peng, Lu Kai
Chin. Phys. B, 2009, 18 (8): 3150-3154 doi: 10.1088/1674-1056/18/8/009
Full Text: [PDF 142 KB] (Downloads:632)
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This paper studies the new type of conserved quantity which is directly induced by Mei symmetry of nonholonomic systems in terms of quasi-coordinates. A coordination function is introduced, and the conditions for the existence of the new conserved quantities as well as their forms are proposed. Some special cases are given to illustrate the generalized significance of the new type conserved quantity. Finally, an illustrated example is given to show the application of the nonholonomic system's results.

Poisson theory of generalized Bikhoff equations

Shang Mei, Mei Feng-Xiang
Chin. Phys. B, 2009, 18 (8): 3155-3157 doi: 10.1088/1674-1056/18/8/010
Full Text: [PDF 123 KB] (Downloads:693)
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This paper presents a Poisson theory of the generalized Birkhoff equations, including the algebraic structure of the equations, the sufficient and necessary condition on the integral and the conditions under which a new integral can be deduced by a known integral as well as the form of the new integral.

Conformal invariance and conserved quantities of general holonomic systems in phase space

Xia Li-Li, Cai Jian-Le, Li Yuan-Cheng
Chin. Phys. B, 2009, 18 (8): 3158-3162 doi: 10.1088/1674-1056/18/8/011
Full Text: [PDF 150 KB] (Downloads:685)
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This paper studies the conformal invariance and conserved quantities of general holonomic systems in phase space. The definition and the determining equation of conformal invariance for general holonomic systems in phase space are provided. The conformal factor expression is deduced from conformal invariance and Lie symmetry. The relationship between the conformal invariance and the Lie symmetry is discussed, and the necessary and sufficient condition that the conformal invariance would be the Lie symmetry of the system under the infinitesimal single-parameter transformation group is deduced. The conserved quantities of the system are given. An example is given to illustrate the application of the result.

Periodic folded waves for (2+1)-dimensional modified dispersive water wave equation

Huang Wen-Hua
Chin. Phys. B, 2009, 18 (8): 3163-3168 doi: 10.1088/1674-1056/18/8/012
Full Text: [PDF 1551 KB] (Downloads:868)
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A general solution, including three arbitrary functions, is obtained for a (2+1)-dimensional modified dispersive water-wave (MDWW) equation by means of the WTC truncation method. Introducing proper multiple valued functions and Jacobi elliptic functions in the seed solution, special types of periodic folded waves are derived. In the long wave limit these periodic folded wave patterns may degenerate into single localized folded solitary wave excitations. The interactions of the periodic folded waves and the degenerated single folded solitary waves are investigated graphically and found to be completely elastic.

Travelling solitary wave solutions for the generalized Burgers--Huxley equation with nonlinear terms of any order

Deng Xi-Jun, Yan Zi-Zong, Han Li-Bo
Chin. Phys. B, 2009, 18 (8): 3169-3173 doi: 10.1088/1674-1056/18/8/013
Full Text: [PDF 162 KB] (Downloads:770)
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In this paper, the travelling wave solutions for the generalized Burgers--Huxley equation with nonlinear terms of any order are studied. By using the first integral method, which is based on the divisor theorem, some exact explicit travelling solitary wave solutions for the above equation are obtained. As a result, some minor errors and some known results in the previousl literature are clarified and improved.

A rigorous criterion to identify the validity of the Born approximation

Li Jian-Bing, Wang Xue-Song, Wang Tao
Chin. Phys. B, 2009, 18 (8): 3174-3182 doi: 10.1088/1674-1056/18/8/014
Full Text: [PDF 754 KB] (Downloads:649)
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This paper intends to identify the validity of the orn approximation by a new universal criterion, which is ultimately reduced to the calculation of an operator norm. With the purpose of enabling the criterion to be applicable to general scattering problems, a method is proposed to estimate the norm of the operator concerned. Compared with the conventional criterion, this method excels in its ability to acquire a quantificational upper bound of the relative error by Born approximation as well as to extend its valid frequency to a wider range. Two canonical scattering examples are given as evidence for the validity of the criterion.

Mode field diameter and nonlinear properties of air-core nanowires

Hu Xiao-Hong, Zhao Wei, Gong Yong-Kang, Wang Lei-Ran, Lu Ke-Qing, Liu Xue-Ming
Chin. Phys. B, 2009, 18 (8): 3183-3188 doi: 10.1088/1674-1056/18/8/015
Full Text: [PDF 212 KB] (Downloads:582)
Show Abstract
Exact solutions of Maxwell's equations describing the lightwave through 3-layer-structured cylindrical waveguide are obtained and the mode field diameter and nonlinear coefficient of air-core nanowires (ACNWs) are numerically calculated. The simulation results show that ACNWs offer some unique optical properties, such as tight field confining ability and extremely high nonlinearity. At a certain wavelength and air core radius, we optimize the waveguide design to maximize the nonlinear coefficient and minimize the mode field diameter. Our results show that the ACNWs may be powerful potential tools for novel micro-photonic devices in the near future.

Secure authentication of classical messages with single photons

Wang Tian-Yin, Wen Qiao-Yan, Zhu Fu-Chen
Chin. Phys. B, 2009, 18 (8): 3189-3192 doi: 10.1088/1674-1056/18/8/016
Full Text: [PDF 143 KB] (Downloads:909)
Show Abstract
This paper proposes a scheme for secure authentication of classical messages with single photons and a hashed function. The security analysis of this scheme is also given, which shows that anyone cannot forge valid message authentication codes (MACs). In addition, the lengths of the authentication key and the MACs are invariable and shorter, in comparison with those presented authentication schemes. Moreover, quantum data storage and entanglement are not required in this scheme. Therefore, this scheme is more efficient and economical.

Controlling nonclassical properties of the two-photon process by a time-varying field

Jia Fei, Xie Shuang-Yuan, Yang Ya-Ping
Chin. Phys. B, 2009, 18 (8): 3193-3202 doi: 10.1088/1674-1056/18/8/017
Full Text: [PDF 295 KB] (Downloads:729)
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The interactions between a two-level atom and a field via two-photon transition without rotating wave approximation have been investigated. We emphasize the dynamic behaviors of the atomic population inversion, the field squeezing, and the atomic dipole squeezing numerically when the field frequency varies with time in the forms of sine and rectangle. Some interesting phenomena are discovered and discussed. The good periodic character of the atomic population inversion in the standard two-photon Jaynes--Cummings model is weakened by the influence of the sine field frequency modulation. The rectangular field frequency modulation can change the correlation among different oscillations suddenly and induce new collapse-revival processes of the atomic population inversion. The field squeezing increases at the beginning of time, but then decreases and loses as the time increases after it reaches the maximum due to the sine modulation. The effects of the rectangular modulation on the field squeezing depend mostly on the appearance time of the modulation. The atomic dipole squeezing is weakened under the influence of the sine or rectangular modulation. Our results indicate that it is possible to perform the dynamic controlling of the system properties by changing the parameters of the system with time. This implies that one can dynamically control a quantum information process by choosing the system modulation properly.

Thermal entanglement and teleportation in a three-qubit Heisenberg XXZ model with Dzyaloshinski--Moriya anisotropic antisymmetric interaction

Xie Li-Jun, Zhang Deng-Yu, Tang Shi-Qing, Zhan Xiao-Gui, Gao Feng
Chin. Phys. B, 2009, 18 (8): 3203-3209 doi: 10.1088/1674-1056/18/8/018
Full Text: [PDF 1671 KB] (Downloads:1040)
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This paper investigates the thermal pairwise entanglement of a three-qubit Heisenberg XXZ chain in the presence of the Dzyaloshinski--Moriya (DM) anisotropic antisymmetric interaction and quantum teleportation when using the Heisenberg chain as a channel. The entanglement dependences on the DM interaction and temperature are given in detail. It obtains the relation between the concurrence and average fidelity, and shows that the same concurrence can lead different average fidelities. Moreover, it finds the thermally entangled states which do not violate the Bell inequalities, and can still be used for quantum teleportation.

Entanglement dynamics of a Heisenberg chain with Dzyaloshinskii--Moriya interaction

Zheng Qiang, Zhang Xiao-Ping, Zhi Qi-Jun, Ren Zhong-Zhou
Chin. Phys. B, 2009, 18 (8): 3210-3214 doi: 10.1088/1674-1056/18/8/019
Full Text: [PDF 195 KB] (Downloads:985)
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This paper investigates the entanglement dynamics of the system, composed of two qubits A and B with Heisenberg XX spin interactation. There is a third controller qubit C, which only has Dzyaloshinskii--Moriya (DM) spin-orbit interaction with the qubit B. It is found that depending on the initial state of the controller qubit C and DM interaction, the entanglement of the system displays amplification and sudden birth effects. These effects indicate that one can control the entanglement of the system, which may be helpful for quantum information processing.

The remote implementation of all possible generalized quantum measurement on single atomic qubit in a quantum network

Han Yang, Wu Chun-Wang, Wu Wei, Chen Ping-Xing, Li Cheng-Zu
Chin. Phys. B, 2009, 18 (8): 3215-3220 doi: 10.1088/1674-1056/18/8/020
Full Text: [PDF 774 KB] (Downloads:778)
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To implement generalized quantum measurement (GQM) one has to extend the original Hilbert space. Generally speaking, the additional dimensions of the ancilla space increase as the number of the operators of the GQM n increases. This paper presents a scheme for deterministically implementing all possible n-operator GQMs on a single atomic qubit by using only one 2-dimensional ancillary atomic qubit repeatedly, which remarkably reduces the complexity of the realistic physical system. Here the qubit is encoded in the internal states of an atom trapped in an optical cavity and single-photon pulses are employed to provide the interaction between qubits. It shows that the scheme can be performed remotely, and thus it is suitable for implementing GQM in a quantum network. What is more, the number of the total ancilla dimensions in our scheme achieves the theoretic low bound.

Effects of three-body interaction on collective excitation and stability of Bose--Einstein condensate

Peng Ping, Li Guan-Qiang
Chin. Phys. B, 2009, 18 (8): 3221-3225 doi: 10.1088/1674-1056/18/8/021
Full Text: [PDF 180 KB] (Downloads:799)
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This paper investigates the collective excitation and stability of low-dimensional Bose--Einstein condensates with two- and three-body interactions by the variational analysis of the time-dependent Gross--Pitaevskii--Ginzburg equation. The spectrum of the low-energy excitation and the effective potential for the width of the condensate are obtained. The results show that: (i) the repulsive two-body interaction among atoms makes the frequency red-shifted for the internal excitation and the repulsive or attractive three-body interaction always makes it blue-shifted; (ii) the region for the existence of the stable bound states is obtained by identifying the critical value of the two- and three-body interactions.

An experimental scheme to verify the dynamics of the Aharonov--Bohm effect

Wang Rui-Feng
Chin. Phys. B, 2009, 18 (8): 3226-3232 doi: 10.1088/1674-1056/18/8/022
Full Text: [PDF 195 KB] (Downloads:636)
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There are two different viewpoints on the Aharonov--Bohm (A--B) effect. One asserts that the A--B effect is due to the existence of the vector potential A. The other asserts that the A--B effect is due to the interaction energy between the magnetic field produced by the moving charges and the magnetic field in the solenoid. The difference of these two viewpoints is analyzed in this paper. To judge which viewpoint is right, this paper suggests a new experimental method.

Economical multiparty simultaneous quantum identity authentication based on Greenberger--Horne--Zeilinger states

Yang Yu-Guang, Wen Qiao-Yan
Chin. Phys. B, 2009, 18 (8): 3233-3237 doi: 10.1088/1674-1056/18/8/023
Full Text: [PDF 152 KB] (Downloads:903)
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A multiparty simultaneous quantum identity authentication protocol based on Greenberger--Horne--Zeilinger (GHZ) states is proposed. The multi-user can be authenticated by a trusted third party (TTP) simultaneously. Compared with the scheme proposed recently (Wang et al 2006, Chin. Phys. Lett. 23(9) 2360), the proposed scheme has the advantages of consuming fewer quantum and classical resources and lessening the difficulty and intensity of necessary operations.

Quantum secret sharing protocol using modulated doubly entangled photons

Wang Chuan, Zhang Yong
Chin. Phys. B, 2009, 18 (8): 3238-3242 doi: 10.1088/1674-1056/18/8/024
Full Text: [PDF 258 KB] (Downloads:586)
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In this paper, we propose a quantum secret sharing protocol utilizing polarization modulated doubly entangled photon pairs. The measurement devices are constructed. By modulating the polarizations of entangled photons, the boss could encode secret information on the initial state and share the photons with different members to realize the secret sharing process. This protocol shows the security against intercept-resend attack and dishonest member cheating. The generalized quantum secret sharing protocol is also discussed.

Local distinguishability by projective measurement

Jiang Wei, Ren Xi-Jun, Zhou Xing-Xiang, Zhou Zheng-Wei, Guo Guang-Can
Chin. Phys. B, 2009, 18 (8): 3243-3246 doi: 10.1088/1674-1056/18/8/025
Full Text: [PDF 160 KB] (Downloads:593)
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This paper proves that a set of orthogonal pure states are indistinguishable by restricted local projective measurement and classical communication if the sum of their Schmidt ranks is larger than the dimension of their joint Hilbert space. This result is useful in determining the local distinguishability of quantum states and is stronger in some respects than that of Hayashi et al [Phys. Rev. Lett. 96, 040501]. In addition, it presents a new method to determine the local distinguishability of orthogonal states by projecting measurement operators into their subspaces.

Transferring an N-atom state between two distant cavities via an optical fiber

Ma Song-She, Chen Mei-Feng
Chin. Phys. B, 2009, 18 (8): 3247-3250 doi: 10.1088/1674-1056/18/8/026
Full Text: [PDF 156 KB] (Downloads:589)
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This paper proposes a scheme for transferring an N-atom state between two distant cavities via an optical fiber. The scheme is based on adiabatic passage along a dark state. In the scheme, all the atoms are always in ground state, the field mode of the fiber remains in vacuum state, and the field mode of the cavities being excited can be negligible under certain conditions. Therefore, the scheme is very robust against decoherence. The successful probability of implementing the quantum state transfer increases with increasing number of atoms. Furthermore, the interaction time does not need to be accurately adjusted as long as the adiabaticity condition is fulfilled.

Effects of intrinsic decoherence on the entanglement of a two-qutrit 1D optical lattice chain with nonlinear coupling

Song Wei
Chin. Phys. B, 2009, 18 (8): 3251-3257 doi: 10.1088/1674-1056/18/8/027
Full Text: [PDF 1583 KB] (Downloads:781)
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We have investigated the intrinsic decoherence on the entanglement of a two-qutrit one-dimensional (1D) optical lattice chain with nonlinear coupling. As a measure of the entanglement, the negativity of the system is calculated. It is shown that the influence of intrinsic decoherence on the entanglement varies in different initial systems.

Three-qubit Fredkin gate based on cavity quantum electrodynamics

Shao Xiao-Qiang, Chen Li, Zhang Shou
Chin. Phys. B, 2009, 18 (8): 3258-3264 doi: 10.1088/1674-1056/18/8/028
Full Text: [PDF 231 KB] (Downloads:723)
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This paper presents a scheme for implementing a Fredkin gate on three modes of a cavity. The scheme is based on the dispersive atom-cavity interaction. By modulating the cavity frequency and the atomic transition frequency appropriately, it obtains the effective form of nonlinear interaction between photons in the three-mode cavity. This availability is testified via numerical analysis. It also considers both the situations with and without dissipation.

Entanglement sudden death induced by the Dzialoshinskii--Moriya interaction

Zeng Hong-Fang, Shao Bin, Yang Lin-Guang, Li Jian, Zou Jian
Chin. Phys. B, 2009, 18 (8): 3265-3270 doi: 10.1088/1674-1056/18/8/029
Full Text: [PDF 978 KB] (Downloads:833)
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In this paper, we study the entanglement dynamics of two-spin Heisenberg XYZ model with the Dzialoshinskii--Moriya (DM) interaction. The system is initially prepared in the Werner state. The effects of purity of the initial state and DM coupling parameter on the evolution of entanglement are investigated. The necessary and sufficient condition for the appearance of the entanglement sudden death (ESD) phenomenon has been deduced. The result shows that the ESD always occurs if the initial state is sufficiently impure for the given coupling parameter or the DM interaction is sufficiently strong for the given initial state. Moreover, the critical values of them are calculated.

A modified weighted probabilistic cellular automaton traffic flow model

Zhuang Qian, Jia Bin, Li Xin-Gang
Chin. Phys. B, 2009, 18 (8): 3271-3278 doi: 10.1088/1674-1056/18/8/030
Full Text: [PDF 3031 KB] (Downloads:818)
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This paper modifies the weighted probabilistic cellular automaton model (Li X L, Kuang H, Song T, et al 2008 Chin. Phys. B 17 2366) which considered a diversity of traffic behaviors under real traffic situations induced by various driving characters and habits. In the new model, the effects of the velocity at the last time step and drivers' desire for acceleration are taken into account. The fundamental diagram, spatial-temporal diagram, and the time series of one-minute data are analyzed. The results show that this model reproduces synchronized flow. Finally, it simulates the on-ramp system with the proposed model. Some characteristics including the phase diagram are studied.

The Onsager reciprocity relation and generalized efficiency of a thermal Brownian motor

Gao Tian-Fu, Zhang Yue, Chen Jin-Can
Chin. Phys. B, 2009, 18 (8): 3279-3286 doi: 10.1088/1674-1056/18/8/031
Full Text: [PDF 234 KB] (Downloads:722)
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Based on a general model of Brownian motors, the Onsager coefficients and generalized efficiency of a thermal Brownian motor are calculated analytically. It is found that the Onsager reciprocity relation holds and the Onsager coefficients are not affected by the kinetic energy change due to the particle's motion. Only when the heat leak in the system is negligible can the determinant of the Onsager matrix vanish. Moreover, the influence of the main parameters characterizing the model on the generalized efficiency of the Brownian motor is discussed in detail. The characteristic curves of the generalized efficiency varying with these parameters are presented, and the maximum generalized efficiency and the corresponding optimum parameters are determined. The results obtained here are of general significance. They are used to analyze the performance characteristics of the Brownian motors operating in the three interesting cases with zero heat leak, zero average drift velocity or a linear response relation, so that some important conclusions in current references are directly included in some limit cases of the present paper.

A method to improve the precision of chaotic time series prediction by using a non-trajectory

Yan Hua, Wei Ping, Xiao Xian-Ci
Chin. Phys. B, 2009, 18 (8): 3287-3294 doi: 10.1088/1674-1056/18/8/032
Full Text: [PDF 212 KB] (Downloads:734)
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Due to the error in the measured value of the initial state and the sensitive dependence on initial conditions of chaotic dynamical systems, the error of chaotic time series prediction increases with the prediction step. This paper provides a method to improve the prediction precision by adjusting the predicted value in the course of iteration according to the evolution information of small intervals on the left and right sides of the predicted value. The adjusted predicted result is a non-trajectory which can provide a better prediction performance than the usual result based on the trajectory. Numerical simulations of two typical chaotic maps demonstrate its effectiveness. When the prediction step gets relatively larger, the effect is more pronounced.

Chaos in fractional-order generalized Lorenz system and its synchronization circuit simulation

Zhang Ruo-Xun, Yang Shi-Ping
Chin. Phys. B, 2009, 18 (8): 3295-3302 doi: 10.1088/1674-1056/18/8/033
Full Text: [PDF 2466 KB] (Downloads:1263)
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The chaotic behaviours of a fractional-order generalized Lorenz system and its synchronization are studied in this paper. A new electronic circuit unit to realize fractional-order operator is proposed. According to the circuit unit, an electronic circuit is designed to realize a 3.8-order generalized Lorenz chaotic system. Furthermore, synchronization between two fractional-order systems is achieved by utilizing a single-variable feedback method. Circuit experiment simulation results verify the effectiveness of the proposed scheme.

Circuitry implementation of a novel nonautonomous hyperchaotic Liu system based on sine input

Luo Xiao-Hua
Chin. Phys. B, 2009, 18 (8): 3304-3308 doi: 10.1088/1674-1056/18/8/034
Full Text: [PDF 684 KB] (Downloads:717)
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Based on the three-dimensional Liu system with a nonlinear term of square, this paper appends a state variable to the system, and further adds a driving signal of the sine signal to construct a novel 4-demensional nonautonomous hyperchaotic Liu system. The appended variable is formed by the product of the nonlinear quadratic term of the original state variables and the driving signal. Through adjusting the frequency of the driving signal, the system can be controlled to show some different dynamic behaviors. By numerical simulations, the Lyapunov exponent spectrums, bifurcation diagrams and phase diagrams of the novel systems are analyzed. Furthermore, the corresponding hardware circuits are implemented. Both the experimental results and the simulation results confirm that the method is feasible. The method, which adjusts the frequency of the input sine signal to control the system to show different dynamic behaviors, can make the dynamic property of the system become more complex, but easier to be controlled accurately as well.

Epidemic spreading on networks with vaccination

Shi Hong-Jing, Duan Zhi-Sheng, Chen Guan-Rong, Li Rong
Chin. Phys. B, 2009, 18 (8): 3309-3317 doi: 10.1088/1674-1056/18/8/035
Full Text: [PDF 315 KB] (Downloads:757)
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In this paper, a new susceptible-infected-susceptible (SIS) model on complex networks with imperfect vaccination is proposed. Two types of epidemic spreading patterns (the recovered individuals have or have not immunity) on scale-free networks are discussed. Both theoretical and numerical analyses are presented. The epidemic thresholds related to the vaccination rate, the vaccination-invalid rate and the vaccination success rate on scale-free networks are demonstrated, showing different results from the reported observations. This reveals that whether or not the epidemic can spread over a network under vaccination control is determined not only by the network structure but also by the medicine's effective duration. Moreover, for a given infective rate, the proportion of individuals to vaccinate can be calculated theoretically for the case that the recovered nodes have immunity. Finally, simulated results are presented to show how to control the disease prevalence.

An experiment of dynamical behaviours in an erbium-doped fibre-ring laser with loss modulation

Liu Yue, Feng Xue, Zhang Wei, Liu Xiao-Ming
Chin. Phys. B, 2009, 18 (8): 3318-3324 doi: 10.1088/1674-1056/18/8/036
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This paper reports a systematic experimental investigation on the dynamics in the low-frequency region in an erbium-doped fibre-ring laser with loss modulation. A rich variety of bifurcation is analyzed through the bifurcation diagram and structured with the concept of the winding numbers. The coexistence of multiple attractors and the crisis that appear in the saddle-node bifurcations, and an interesting structure of bifurcation which is similar to the bifurcations in high-frequency range, have been observed.

Robust stability analysis for Markovian jumping stochastic neural networks with mode-dependent time-varying interval delay and multiplicative noise

Zhang Hua-Guang, Fu Jie, Ma Tie-Dong, Tong Shao-Cheng
Chin. Phys. B, 2009, 18 (8): 3325-3336 doi: 10.1088/1674-1056/18/8/037
Full Text: [PDF 192 KB] (Downloads:442)
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This paper is concerned with the problem of robust stability for a class of Markovian jumping stochastic neural networks (MJSNNs) subject to mode-dependent time-varying interval delay and state-multiplicative noise. Based on the Lyapunov--Krasovskii functional and a stochastic analysis approach, some new delay-dependent sufficient conditions are obtained in the linear matrix inequality (LMI) format such that delayed MJSNNs are globally asymptotically stable in the mean-square sense for all admissible uncertainties. An important feature of the results is that the stability criteria are dependent on not only the lower bound and upper bound of delay for all modes but also the covariance matrix consisting of the correlation coefficient. Numerical examples are given to illustrate the effectiveness.

Pinning-controlled synchronization of complex networks with bounded or unbounded synchronized regions

Zou Yan-Li, Chen Guan-Rong
Chin. Phys. B, 2009, 18 (8): 3337-3346 doi: 10.1088/1674-1056/18/8/038
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This paper studies pinning-controlled synchronization of complex networks with bounded or unbounded synchronized regions. To study a state-feedback pinning-controlled network with N nodes, it first converts the controlled network to an extended network of N+1 nodes without controls. It is shown that the controlled synchronizability of the given network is determined by the real part of the smallest nonzero eigenvalue of the coupling matrix of its extended network when the synchronized region is unbounded; but it is determined by the ratio of the real parts of the largest and the smallest nonzero eigenvalues of the coupling matrix when the synchronized region is bounded. Both theoretical analysis and numerical simulation show that the portion of controlled nodes has no critical values when the synchronized region is unbounded, but it has a critical value when the synchronized region is bounded. In the former case, therefore, it is possible to control the network to achieve synchronization by pinning only one node. In the latter case, the network can achieve controlled synchronization only when the portion of controlled nodes is larger than the critical value.

The effect of stochastic accelerating and delay probability with the velocity and the gap between vehicles on traffic flow

Sheng Peng, Zhao Shu-Long, Wang Jun-Feng, Tang Peng, Gao Lin
Chin. Phys. B, 2009, 18 (8): 3347-3354 doi: 10.1088/1674-1056/18/8/039
Full Text: [PDF 4146 KB] (Downloads:765)
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This paper proposes a new combined cellular automaton (CA) model considering the driver behavior of stochastic acceleration and delay with the velocity of the preceding vehicle and the gap between the successive vehicles based on the WWH model and the noise-first NaSch model. It introduces the delay probability varying with the gap, adds the anticipation headway and increases the acceleration with a certain probability. Through these simulations, not only can the metastable state and start--stop wave be obtained but also the synchronized flow which the wide moving jam results in. Moreover, the effect of stochastic acceleration and delay on traffic flow is discussed by analyzing the correlation of traffic data. This indicates that synchronized flow easily emerges in the critical area between free flow and synchronized flow when acceleration and delay are synchronized or their probability is close to 0.5.

Nonlinear consensus protocols for multi-agent systems based on centre manifold reduction

Li Yu-Mei, Guan Xin-Ping
Chin. Phys. B, 2009, 18 (8): 3355-3366 doi: 10.1088/1674-1056/18/8/040
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Nonlinear consensus protocols for dynamic directed networks of multi-agent systems with fixed and switching topologies are investigated separately in this paper. Based on the centre manifold reduction technique, nonlinear consensus protocols are presented. We prove that a group of agents can reach a β-consensus, the value of which is the group decision value varying from the minimum and the maximum values of the initial states of the agents. Moreover, we derive the conditions to guarantee that all the agents reach a β--consensus on a desired group decision value. Finally, a simulation study concerning the vertical alignment manoeuvere of a team of unmanned air vehicles is performed. Simulation results show that the nonlinear consensus protocols proposed are more effective than the linear protocols for the formation control of the agents and they are an improvement over existing protocols.

Plasma characterization on carbon fiber cathode by spectroscopic diagnostics

Liu Lie, Li Li-Min, Xu Qi-Fu, Chang Lei, Wen Jian-Chun
Chin. Phys. B, 2009, 18 (8): 3367-3372 doi: 10.1088/1674-1056/18/8/041
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This paper mainly investigates plasma characterization on carbon fiber cathodes with and without cesium iodide (CsI) coating powered by a ~300~ns, ~ 200~kV accelerating pulse. It was found that the CsI layers can not only improve the diode voltage, but also maintain a stable perveance. This indicates a slowly changed diode gap or a low cathode plasma expansion velocity. By spectroscopic diagnostics, in the vicinity of the cathode surface the average plasma density and temperature were found to be ~ 3× 1014~cm-3 and ~ 5~eV, respectively, for an electron current density of ~ 40~A/cm2. Furthermore, there exists a multicomponent plasma expansion toward the anode. The plasma expansion velocity, corresponding to the carbon and hydrogen ions, is estimated to be ~ 1.5~cm/μ s. Most notably, Cs spectroscopic line was obtained only at the distance ≤ 0.5~mm from the cathode surface. Carbon and hydrogen ions are obtained up to the distance of 2.5~mm from the cathode surface. Cs ions almost remain at the vicinity of the cathode surface. These results show that the addition of CsI enables a slow cathode plasma expansion toward the anode, providing a positive prospect for developing long-pulse electron beam sources.

Characterization of a velocity-tunable 87Rb cold atomic source with a high-speed imaging technology

Feng Yan-Ying, Zhu Chang-Xing, Wang Xiao-Jia, Xue Hong-Bo, Ye Xiong-Ying, Zhou Zhao-Ying
Chin. Phys. B, 2009, 18 (8): 3373-3378 doi: 10.1088/1674-1056/18/8/042
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This paper has developed and characterized a method to produce a velocity-tunable 87Rb cold atomic source for atomic interferometry application. Using a high speed fluorescence imaging technology, it reports that the dynamic process of the atomic source formation is observed and the source performances including the flux and the initial velocity are characterized. A tunable atomic source with the initial velocity of 1.4~ 2.6~m/s and the atomic source flux of 2× 108~ 6× 109 atoms/s has been obtained with the built experimental setup.
RAPID COMMUNICATION

Long-distance quantum teleportation assisted with free-space entanglement distribution Hot!

Ren Ji-Gang, Yang Bin, Yi Zhen-Huan, Zhou Fei, Chen Kai, Peng Cheng-Zhi, Pan Jian-Wei
Chin. Phys. B, 2009, 18 (8): 3605-3610 doi: 10.1088/1674-1056/18/8/078
Full Text: [PDF 1361 KB] (Downloads:907)
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Faithful long-distance quantum teleportation necessitates prior entanglement distribution between two communicated locations. The particle carrying on the unknown quantum information is then combined with one particle of the entangled states for Bell-state measurements, which leads to a transfer of the original quantum information onto the other particle of the entangled states. However in most of the implemented teleportation experiments nowadays, the Bell-state measurements are performed even before successful distribution of entanglement. This leads to an instant collapse of the quantum state for the transmitted particle, which is actually a single-particle transmission thereafter. Thus the true distance for quantum teleportation is, in fact, only in a level of meters. In the present experiment we design a novel scheme which has overcome this limit by utilizing fiber as quantum memory. A complete quantum teleportation is achieved upon successful entanglement distribution over 967 meters in public free space. Active feed-forward control techniques are developed for real-time transfer of quantum information. The overall experimental fidelities for teleported states are better than 89.6%, which signify high-quality teleportation.
CLASSICAL AREAS OF PHENOMENOLOGY

Electromagnetic scattering from two-layer rough interfaces in the Kirchhoff approximation

Wang Rui, Guo Li-Xin, Ma Jun
Chin. Phys. B, 2009, 18 (8): 3422-3430 doi: 10.1088/1674-1056/18/8/049
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Electromagnetic wave scattering from multilayers consisting of two two-layer Gaussian rough surfaces with lossless media is investigated in the Kirchhoff approximation (KA), with consideration of the shadowing effects. The tapered incident wave is introduced into the classic KA, and the bistatic scattering coefficient is redetermined. The advantage of this method is that it is faster in computation than the exact numerical methods. The numerical results show that the bistatic scattering coefficient calculated in the KA is in good agreement with that obtained by using the method of moment (MOM) over a most angular range, which indicates the validity of the KA proposed in our paper. Finally, the effects of the relative permittivity, the root-mean-square (RMS) height, the correlative length, and the average height between the two interfaces on the bistatic scattering coefficient are discussed in detail.

Study of MPI based on parallel MOM on PC clusters for EM-beam scattering by 2-D PEC rough surfaces

Ma Jun, Guo Li-Xin, Wang An-Qi
Chin. Phys. B, 2009, 18 (8): 3431-3437 doi: 10.1088/1674-1056/18/8/050
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This paper firstly applies the finite impulse response filter (FIR) theory combined with the fast Fourier transform (FFT) method to generate two-dimensional Gaussian rough surface. Using the electric field integral equation (EFIE), it introduces the method of moment (MOM) with RWG vector basis function and Galerkin's method to investigate the electromagnetic beam scattering by a two-dimensional PEC Gaussian rough surface on personal computer (PC) clusters. The details of the parallel conjugate gradient method (CGM) for solving the matrix equation are also presented and the numerical simulations are obtained through the message passing interface (MPI) platform on the PC clusters. It finds significantly that the parallel MOM supplies a novel technique for solving a two-dimensional rough surface electromagnetic-scattering problem. The influences of the root-mean-square height, the correlation length and the polarization on the beam scattering characteristics by two-dimensional PEC Gaussian rough surfaces are finally discussed.

External-cavity birefringence feedback effects of microchip Nd:YAG laser and its application in angle measurement

Ren Cheng, Tan Yi-Dong, Zhang Shu-Lian
Chin. Phys. B, 2009, 18 (8): 3438-3443 doi: 10.1088/1674-1056/18/8/051
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External-cavity birefringence feedback effects of the microchip Nd:YAG laser are presented. When a birefringence element is placed in the external feedback cavity of the laser, two orthogonally polarized laser beams with a phase difference are output. The phase difference is twice as large as the phase retardation in the external cavity along the two orthogonal directions. The variable extra-cavity birefringence, caused by rotation of the external-cavity birefringence element, results in tunable phase difference between the two orthogonally polarized beams. This means that the roll angle information has been translated to phase difference of two output laser beams. A theoretical analysis based on the Fabry--Perot cavity equivalent model and refractive index ellipsoid is presented, which is in good agreement with the experimental results. This phenomenon has potential applications for roll angle measurement.

Quantum interference between Raman scattering and single-photon absorption

Li Yan-Rong, Wang Yun-Ping
Chin. Phys. B, 2009, 18 (8): 3444-3448 doi: 10.1088/1674-1056/18/8/052
Full Text: [PDF 310 KB] (Downloads:439)
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A new kind of quantum interference between Raman scattering and single-photon absorption is predicted theoretically, which gives an expanded view of quantum interference. Its potential application is also proposed.

155~Mb/s--10~Gb/s combined FSK-IM/optical label-packet modulation signals 100~km transmission over standard single mode fiber using mid-span spectral inversion by four-wave mixing in an SOA

Xin Xiang-Jun, Ma Jian-Xin, Zhang Qi, Deng Chao-Gong, Wang Kui-Ru, Yu Chong-Xiu, Liu Bo
Chin. Phys. B, 2009, 18 (8): 3449-3452 doi: 10.1088/1674-1056/18/8/053
Full Text: [PDF 994 KB] (Downloads:841)
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This paper introduces the mid-span spectral inversion by four-wave mixing in a commercially available semiconductor optical amplifier (SOA) with a length of about 1.5~mm to optical label switching network based on combined frequency shift keying (FSK)-intensiy modulation (IM)/optical label-packet modulation to overcome the dispersion limitation of fiber. The 155~Mb/s--10~Gb/s combined FSK/IM signal is experimentally transmitted over a 100~km standard single mode fiber. 10-10 and 109 BER (bit error ratio), or even better, is achieved for the FSK label and IM packet, respectively. The -19~dB power conversion efficiency is obtained for -1~nm wavelength detuning.

Robust scheme for implemention of quantum phase gates for two atoms

Zheng Shi-Biao
Chin. Phys. B, 2009, 18 (8): 3453-3456 doi: 10.1088/1674-1056/18/8/054
Full Text: [PDF 196 KB] (Downloads:486)
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We propose a scheme for implementing conditional quantum phase gates for two four-state atoms trapped in a cavity. The two ground states of the atoms are coupled through two Raman processes induced by the cavity mode and two classical fields. Under certain conditions nonresonant Raman processes lead to two-atom coupling and can be used to produce conditional phase gates. The scheme is insensitive to cavity decay, thermal photons, and atomic spontaneous emission. The scheme does not require individual addressing of the atoms.

Atomic emission spectra and field non-classical properties

Tang Pei, Guo Hong
Chin. Phys. B, 2009, 18 (8): 3457-3465 doi: 10.1088/1674-1056/18/8/055
Full Text: [PDF 335 KB] (Downloads:448)
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This paper studies the interaction of a Λ-type three-level atom with a single mode field. It discusses the emission spectrum characteristics of the Λ -type three-level atom driven by the photon-added coherent field. By means of the second-order degree of coherence, it shows some nonclassical properties of the cavity field, such as sub-Poissonian photon-number distribution and the two-time intensity--intensity correlation which violates the Cauchy--Schwarz inequality.

The influence of nonparaxiality on the spectral behavior in Young's experiment illuminated by partially coherent light

Zhao Guang-Pu, Lü Bai-Da
Chin. Phys. B, 2009, 18 (8): 3466-3472 doi: 10.1088/1674-1056/18/8/056
Full Text: [PDF 246 KB] (Downloads:524)
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Starting from the Rayleigh--Sommerfeld diffraction integral, this paper studies the spectral behavior in Young's experiment illuminated by nonparaxial partially coherent light and compares with the paraxial case, where the influence of nonparaxiality of partially coherent light on the spectral shifts and spectral switches is stressed. It is shown that there is a spectral shift in the nonparaxial case relative to the paraxial one and the critical position changes, at which the spectral switch occurs. The ratio of the waist width to the central wavelength w00 and relative spatial correlation length \De affect the spectral difference. The smaller w00 is, the larger the difference between the nonparaxial and paraxial results appears. The effect of relative spatial correlation length Δ is relatively small.
ATOMIC AND MOLECULAR PHYSICS

Experimental study of highly excited even-parity bound states of the Sm atom

Qin Wen-Jie, Dai Chang-Jian, Xiao Ying, Zhao Hong-Ying
Chin. Phys. B, 2009, 18 (8): 3384-3394 doi: 10.1088/1674-1056/18/8/044
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In this work, a three-step autoionization detection method and direct photoionization detection method are employed to measure the highly excited even-parity states of the Sm atom in the energy region between 36360~cm-1 and 40800~cm-1. Comparisons between the results from the two detection techniques enable us to discriminate the Rydberg states from the valence states in the same energy region with the information of level energies, possible J values and their relative intensities. Furthermore, in the experiment two different excitation schemes are designed to obtain the spectra of highly excited even-parity states of the Sm atom. With a detailed analysis of the experimental data, this work not only confirms the results about many spectral data from the literature with different excitation schemes, but also reports new spectral data on 29 Rydberg states and 23 valence states.

Kinetic theory of (2+4)-level atom in σ+- laser fields

Yu Chuang, Yu De-Shui, Chen Jing-Biao
Chin. Phys. B, 2009, 18 (8): 3395-3403 doi: 10.1088/1674-1056/18/8/045
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The kinetic theory of (2+4)-level atoms in σ+- laser fields is presented. We systemically discuss friction coefficient, momentum diffusion tensor and atomic temperature based on the Fokker--Planck equation. This cooling system is much like that of a (1+3)-level atom, and the temperature is still limited to the Doppler temperature. Since this cooling system has not been investigated before, this work may be regarded as a necessary complement to the laser cooling theory.

Single atoms transferring between a magneto-optical trap and a far-off-resonance optical dipole trap Hot!

He Jun, Wang Jing, Yang Bao-Dong, Zhang Tian-Cai, Wang Jun-Min
Chin. Phys. B, 2009, 18 (8): 3404-3408 doi: 10.1088/1674-1056/18/8/046
Full Text: [PDF 202 KB] (Downloads:628)
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Based on our work on single cesium atoms trapped in a large-magnetic-gradient vapour-cell magneto-optical trap (MOT), the signal-to-noise ratio (SNR) is remarkably improved. Also a far-off-resonance optical dipole trap (FORT) formed by a strongly-focused 1064~nm single frequency Nd:YVO4 laser beam is introduced. One cesium atom is prepared in the MOT, and then it can transfer successfully between the MOT and the FORT which is overlapped with the MOT. Utilizing the effective transfer, the lifetime of single atoms trapped in the FORT is measured to be 6.9± 0.3~s. Thus we provide a system where the atomic qubit can be coherently manipulated.

Dielectronic recombination of Co-like tantalum

Zhou Li, Meng Fan-Chang, Huang Min, Chen Chong-Yang, Wang Yan-Sen
Chin. Phys. B, 2009, 18 (8): 3409-3413 doi: 10.1088/1674-1056/18/8/047
Full Text: [PDF 569 KB] (Downloads:633)
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Ab initio calculation of the total dielectronic recombination (DR) rate coefficient from the ground state of Co-like tantalum is performed using the relativistic distorted-wave approximation with configuration interaction. The contributions to the total DR rate coefficients are explicitly calculated from the complexes of Ni-like tantalum: 3s23p63d3/23 3d5/26 n'l', 3s23p53d10n'l', 3s3p63d10n'l', 3s23p63d84ln'l', 3s23p53d94ln'l' and 3s3p63d94ln'l' with n' ≤ 25, and 3s23p63d85ln'l' with n' ≤ 9. The l' and n' dependences of partial DR rate coefficients are investigated. The contributions from higher n'complexes are evaluated by a level-by-level extrapolation method. The total DR rate coefficients mainly come from the complex series 3s23p63d84ln'l', 3s23p53d94ln'l' and are fitted to an empirical formula with high accuracy. Comparison of the present results with those of other works shows that the previously published data underestimate significantly the DR rates of Co-like tantalum.

Static dipole polarizabilities of Scn (n≤15) clusters

Li Xi-Bo, Wang Hong-Yan, Luo Jiang-Shan, Guo Yun-Dong, Wu Wei-Dong, Tang Yong-Jian
Chin. Phys. B, 2009, 18 (8): 3414-3421 doi: 10.1088/1674-1056/18/8/048
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The static dipole polarizabilities of scandium clusters with up to 15 atoms are determined by using the numerically finite field method in the framework of density functional theory. The electronic effects on the polarizabilities are investigated for the scandium clusters. We examine a large highest occupied molecular orbital --- the lowest occupied molecular orbital (HOMO--LUMO) gap of a scandium cluster usually corresponds to a large dipole moment. The static polarizability per atom decreases slowly and exhibits local minimum with increasing cluster size. The polarizability anisotropy and the ratio of mean static polarizability to the HOMO--LUMO gap can also reflect the cluster stability. The polarizability of the scandium cluster is partially related to the HOMO--LUMO gap and is also dependent on geometrical characteristics. A strong correlation between the polarizability and ionization energy is observed.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Topological aspects in a two-component Bose condensed system in neutron star

Ren Ji-Rong, Guo Heng
Chin. Phys. B, 2009, 18 (8): 3379-3383 doi: 10.1088/1674-1056/18/8/043
Full Text: [PDF 165 KB] (Downloads:506)
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By making use of Duan--Ge's decomposition theory of gauge potential and the topological current theory proposed by Prof. Duan Yi-Shi, we study a two-component superfluid Bose condensed system, which is supposed to be realized in the interior of neutron stars in the form of the coexistence of a neutron superfluid and a protonic superconductor. We propose that this system possesses vortex lines. The topological charges of the vortex lines are characterized by the Hopf indices and the Brower degrees of φ-mapping.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Density and impurity profile behaviours in HL-2A tokamak with different gas fuelling methods

Cui Zheng-Ying, Zhou Yan, Li Wei, Feng Bei-Bin, Sun Ping, Dong Chun-Feng, Liu Yi, Hong Wen-Yu, Yang Qing-Wei, Ding Xuan-Tong, Duan Xu-Ru
Chin. Phys. B, 2009, 18 (8): 3473-3483 doi: 10.1088/1674-1056/18/8/057
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The electron density profile peaking and the impurity accumulation in the HL-2A tokamak plasma are observed when three kinds of fuelling methods are separately used at different fuelling particle locations. The density profile becomes more peaked when the line-averaged electron density approaches the Greenwald density limit nG and, consequently, impurity accumulation is often observed. A linear increase regime in the density range ne< 0.6nG and a saturation regime in ne > 0.6nG are obtained. There is no significant difference in achieved density peaking factor fne between the supersonic molecular beam injection (SMBI) and gas puffing into the plasma main chamber. However, the achieved fne is relatively low, in particular, in the case of density below 0.7nG, when the working gas is puffed into the divertor chamber. A discharge with a density as high as 1.2nG, i.e. ne = 1.2nG, can be achieved by SMBI just after siliconization as a wall conditioning. The metallic impurities, such as iron and chromium, also increase remarkably when the impurity accumulation happens. The mechanism behind the density peaking and impurity accumulation is studied by investigating both the density peaking factor versus the effective collisionality and the radiation peaking versus density peaking.

A numerical simulation of surface wave excitation in a rectangular planar-type plasma source

Chen Zhao-Quan, Liu Ming-Hai, Lan Chao-Hui, Chen Wei, Tang Liang, Luo Zhi-Qing, Yan Bao-Rong, Lü Jian-Hong, Hu Xi-Wei
Chin. Phys. B, 2009, 18 (8): 3484-3489 doi: 10.1088/1674-1056/18/8/058
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The principle of surface wave plasma discharge in a rectangular cavity is introduced simply based on surface plasmon polariton theory. The distribution of surface-wave electric field at the interface of the plasma-dielectric slab is investigated by using the three-dimensional finite-difference time-domain method (3D-FDTD) with different slot-antenna structures. And the experimental image of discharge with a novel slot antenna array and the simulation of the electric field with this slot antenna array are both displayed. Combined with the distribution of surface wave excitation and experimental results, the numerical simulation performed by using 3D-FDTD is shown to be a useful tool in the computer-aided antenna design for large area planar-type surface-wave plasma sources.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

High energy electron radiation effect on Ni/4H-SiC SBD and Ohmic contact

Zhang Lin, Zhang Yi-Men, Zhang Yu-Ming, Han Chao, Ma Yong-Ji
Chin. Phys. B, 2009, 18 (8): 3490-3494 doi: 10.1088/1674-1056/18/8/059
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The Ni/4H-SiC Schottky barrier diodes (SBDs) and transfer length method (TLM) test patterns of Ni/4H-SiC Ohmic contacts were fabricated, and irradiated with 1~MeV electrons up to a dose of 3.43× 1014~e/cm-2. After radiation, the forward currents of the SBDs at 2~V decreased by about 50%, and the reverse currents at -200~V increased by less than 30%. Schottky barrier height (φ B ) of the Ni/4H-SiC SBD increased from 1.20~eV to 1.21~eV under 0~V irradiation bias, and decreased from 1.25~eV to 1.19~eV under -30~V irradiation bias. The degradation of φ B could be explained by the variation of interface states of Schottky contacts. The on-state resistance (Rs) and the reverse current increased with the dose, which can be ascribed to the radiation defects in bulk material. The specific contact resistance (\rhoc) of the Ni/SiC Ohmic contact increased from 5.11× 105~Ωega.cm2 to 2.97× 10-4~Ωega.cm2.

Pseudo-potential investigations of structural, elastic and thermal properties of tungsten disilicide

Xu Guo-Liang, Chen Jing-Dong, Xia Yao-Zheng, Liu Xue-Feng
Chin. Phys. B, 2009, 18 (8): 3495-3499 doi: 10.1088/1674-1056/18/8/060
Full Text: [PDF 493 KB] (Downloads:1157)
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The plane-wave pseudopotential method using the generalized gradient approximation within the density functional theory is used to investigate the structure and bulk modulus of WSi2. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained with the plane-wave pseudopotential method, is applied to the study of the elastic properties and vibrational effects. We have analysed the bulk modulus of WSi2 up to 1600~K. The major trend shows that the WSi2 crystal becomes more compressible when the temperature rises and the increase of compressibility leads to the decrease of Debye temperature. The predicted temperature and pressure effects on the thermal expansion, heat capacity and Debye temperatures are determined from the non-equilibrium Gibbs functions and compared with the data available.

Influence of solute cloud and precipitates on spatiotemporal characteristics of Portevin-Le Chatelier effect in A2024 aluminum alloys

Sun Liang, Zhang Qing-Chuan, Cao Peng-Tao
Chin. Phys. B, 2009, 18 (8): 3500-3507 doi: 10.1088/1674-1056/18/8/061
Full Text: [PDF 3799 KB] (Downloads:1007)
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In this paper, solute concentration and precipitate content in A2024 aluminum alloy are adjusted by solution treatment (ST) at different temperatures and tensile experiments on these treated specimens are carried out. It is found that the temperature of solution treatment (ST temperature) has a remarkable influence on the amplitude of the serrated flow and the propagation characteristics of shear bands. These results are due to the effects of solute atoms and precipitates on dynamic strain aging (DSA). When ST temperature is higher than 300~℃, solute concentration is relatively high and solute cloud is a key factor of DSA. When ST temperature is lower than 300~℃, precipitate content is relatively high and the mechanism of DSA is determined by precipitates.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Fourier transform technique in variational treatment of two-electron parabolic quantum dot

S. ?akiro?lu, A. Y1ld1z, ü. Do?an, K. Akgüng?r, H. Epik, Y. Ergün, H. Sar1, ?. S?kmen
Chin. Phys. B, 2009, 18 (8): 3508-3516 doi: 10.1088/1674-1056/18/8/062
Full Text: [PDF 212 KB] (Downloads:612)
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In this work, we propose an efficient method of reducing the computational effort of variational calculation with a Hylleraas-like trial wavefunction. The method consists of introducing integral transforms for the terms as r12^k\exp(-λ r12) which provide the calculation of the expectation value of energy and the relevant matrix elements to be done analytically over single-electron coordinates instead of Hylleraas coordinates. We have used this method to calculate the ground state energy of a two-electron system in a spherical dot and a disk-like quantum dot separately. Under parabolic confinement potential and within effective mass approximation size and shape effects of quantum dots on the ground state energy of two electrons have been investigated. The calculation shows that our results even with a small number of basis states are in good agreement with previous theoretical results.

Coherent field emission from a multi-walled carbon nanotube with two open-ended branches

Bai Xin, Zhang Geng-Min, Wang Ming-Sheng, Zhang Zhao-Xiang, Yu Jie, Zhao Xing-Yu, Guo Deng-Zhu, Xue Zeng-Quan
Chin. Phys. B, 2009, 18 (8): 3517-3522 doi: 10.1088/1674-1056/18/8/063
Full Text: [PDF 4264 KB] (Downloads:553)
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Interference fringes are obtained in a field-emission microscopy (FEM) study of a multi-walled carbon nanotube (MWCNT) with two open-ended branches. The FEM pattern, which is composed of three parallel streaks, can be interpreted by using classical Young's double-slit interference with the ends of the two MWCNT branches treated as two secondary sources of the electron wave. The origin of the coherency of the electron beams from the two branches is discussed on the basis of the quantitative analysis of the FEM pattern. The result suggests a new approach to obtaining a coherent electron source.

Kinetic magnetoelectric effect in laterally boundary-confined ballistic two-dimensional hole gases

Huang Hai-Tao, Hu Liang-Bin, Zhang Xin-Ding, Zhu Shi-Liang
Chin. Phys. B, 2009, 18 (8): 3523-3529 doi: 10.1088/1674-1056/18/8/064
Full Text: [PDF 197 KB] (Downloads:488)
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A theoretical investigation is presented on the characteristics of the kinetic magnetoelectric effect in laterally boundary-confined ballistic two-dimensional hole gases. It was shown that, though the momentum-dependent effective magnetic fields felt by charge carriers due to the spin-orbit interaction are in-plane orientated in such systems, both in-plane polarized and normal polarized nonequilibrium spin polarization densities could be electrically induced by the kinetic magnetoelectric effect, and the induced nonequilibrium spin polarizations exhibit some interesting characteristics. The characteristics we found indicate that there may be some possible relation between this effect and some recent experimental findings.

Study of top and bottom contact resistance in one organic field-effect transistor

Liu Ge, Liu Ming, Wang Hong, Shang Li-Wei, Ji Zhuo-Yu, Liu Xing-Hua, Liu Jiang
Chin. Phys. B, 2009, 18 (8): 3530-3534 doi: 10.1088/1674-1056/18/8/065
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This paper reports that the organic field-effect transistors with hybrid contact geometry were fabricated, in which the top electrodes and the bottom electrodes were combined in parallel resistances within one transistor. With the facility of the novel structure, the difference of contact resistance between the top contact geometry and the bottom contact geometry was studied. The hybrid contact devices showed similar characteristics with the top contact configuration devices, which provide helpful evidence on the lower contact resistance of the top contact configuration device. The origin of the different contact resistance between the top contact device and the bottom contact device was discussed.

Long-range surface plasmon polaritons with subwavelength mode expansion in an asymmetrical system

Chen Jian-Jun, Li Zhi, Gong Qi-Huang
Chin. Phys. B, 2009, 18 (8): 3535-3541 doi: 10.1088/1674-1056/18/8/066
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Long-range surface plasmon polariton (LRSPP) modes in an asymmetrical system, in which the thin metal film is sandwiched between a semi-infinite substrate and a high permittivity polymer film with a finite thickness, are theoretically calculated and analyzed. Due to the high permittivity of the polymer film, at proper polymer film thicknesses, the index-matching condition of the dielectrics at both sides of the metal can be satisfied for supporting LRSPP modes, and the electromagnetic field above the metal can be localized well. It is found that these LRSPP modes have both long propagation lengths and subwavelength mode expansion above the metal at the optimal polymer film thicknesses. Furthermore, the requirements on the refractive index and the thickness of the polymer film to support LRSPP modes at the optimal thicknesses are found to be not critical.

Annealing effects on the structure and electrical characteristics of amorphous Er2O3 films

Fang Ze-Bo, Zhu Yan-Yan, Wang Jia-Le, Jiang Zui-Min
Chin. Phys. B, 2009, 18 (8): 3542-3546 doi: 10.1088/1674-1056/18/8/067
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Amorphous Er2O3 films are deposited on Si (001) substrates by using reactive evaporation. This paper reports the evolution of the structure, morphology and electrical characteristics with annealing temperatures in an oxygen ambience. X-ray diffraction and high resolution transimission electron microscopy measurement show that the films remain amorphous even after annealing at 700℃. The capacitance in the accumulation region of Er2O3 films annealed at 450℃ is higher than that of as-deposited films and films annealed at other temperatures. An Er2O3/ErOx/SiOx/Si structure model is proposed to explain the results. The annealed films also exhibit a low leakage current density (around 1.38× 10-4~A/cm2 at a bias of -1~V) due to the evolution of morphology and composition of the films after they are annealed.

Quantum fluctuations of the antiferro-antiferromagnetic double-layer

Jiang Wei, Zhu Cheng-Bo, Yu Gui-Hong, Lo Veng-Cheong
Chin. Phys. B, 2009, 18 (8): 3547-3550 doi: 10.1088/1674-1056/18/8/068
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This paper stuides the magnetization and quantum fluctuations of an antiferro-antiferromagnetic (AF-AF) double-layer at zero temperature. It is found that the exchanges and anisotropy constants affect the quantum fluctuations of spins. If the anisotropy exists, there will be no acoustic energy branch in the system. The anisotropy constant, antiferromagnetic intralayer and interlayer coupling have important roles in a balance of the quantum competition.

Electron spin resonance investigation of the substitution of Fe3+ for Ti4+ ions in rutile TiO2 single crystal

Li Guo-Ke, Zhang Xiang-Qun, Wu Hong-Ye, Huang Wan-Guo, Jin Jin-Ling, Sun Young, Cheng Zhao-Hua
Chin. Phys. B, 2009, 18 (8): 3551-3554 doi: 10.1088/1674-1056/18/8/069
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A Fe doped rutile TiO2 single crystal is grown in an O2 atmosphere by the floating zone technique. Electron spin resonance (ESR) spectra clearly demonstrate that Fe3+ ions are substituted for the Ti4+ ions in the rutile TiO2 matrix. Magnetization measurements reveal that the Fe:TiO2 crystal shows paramagnetic behaviour in a temperature range from 5~K to 350~K. The Fe3+ ions possess weak magnetic anisotropy with an easy axis along the c axis. The annealed Fe:TiO2 crystal shows spin-glass-like behaviours due to the aggregation of the ferromagnetic clusters.

Structure and luminescence of Ca2Si5N8:Eu2+ phosphor for warm white light-emitting diodes

Wei Xiao-Dan, Cai Li-Yan, Lu Fa-Chun, Chen Xiao-Long, Chen Xue-Yuan, Liu Quan-Lin
Chin. Phys. B, 2009, 18 (8): 3555-3562 doi: 10.1088/1674-1056/18/8/070
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We have synthesized Ca2Si5N8:Eu2+ phosphor through a solid-state reaction and investigated its structural and luminescent properties. Our Rietveld refinement of the crystal structure of Ca2Si5N8 reveals that Eu atoms substituting for Ca atoms occupy two crystallographic positions. Between 10~K and 300~K, Ca2Si5N8:Eu2+ phosphor shows a broad red emission band centred at ~1.97~eV--2.01~eV. The gravity centre of the excitation band is located at 3.0~eV--3.31~eV. The centroid shift of the 5d levels of Eu2+ is determined to be ~ 1.17~eV, and the red-shift of the lowest absorption band to be ~ 0.54~eV due to the crystal field splitting. We have analysed the temperature dependence of PL by using a configuration coordinate model. The Huang--Rhys parameter S=6.0, the phonon energy \hbar υ =52~meV, and the Stokes shift Δ S=0.57~eV are obtained. The emission intensity maximum occurring at ~ 200~K can be explained by a trapping effect. Both photoluminescence (PL) emission intensity and decay time decrease with temperature increasing beyond 200~K due to the non-radiative process.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Accurate and rapid error estimation on global gravitational field from current GRACE and future GRACE Follow-On missions

Zheng Wei, Hsu Hou-Tse, Zhong Min, Yun Mei-Juan
Chin. Phys. B, 2009, 18 (8): 3597-3604 doi: 10.1088/1674-1056/18/8/077
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Firstly, the new combined error model of cumulative geoid height influenced by four error sources, including the inter-satellite range-rate of an interferometric laser (K-band) ranging system, the orbital position and velocity of a global positioning system (GPS) receiver and non-conservative force of an accelerometer, is established from the perspectives of the power spectrum principle in physics using the semi-analytical approach. Secondly, the accuracy of the global gravitational field is accurately and rapidly estimated based on the combined error model; the cumulative geoid height error is 1.985× 10-1~m at degree 120 based on GRACE Level 1B measured observation errors of the year 2007 published by the US Jet Propulsion Laboratory (JPL), and the cumulative geoid height error is 5.825× 10^ - 2~m at degree 360 using GRACE Follow-On orbital altitude 250~km and inter-satellite range 50 km. The matching relationship of accuracy indexes from GRACE Follow-On key payloads is brought forward, and the dependability of the combined error model is validated. Finally, the feasibility of high-accuracy and high-resolution global gravitational field estimation from GRACE Follow-On is demonstrated based on different satellite orbital altitudes.
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