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Chin. Phys. B  
  Chin. Phys. B--2007, Vol.16, No.8
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GENERAL

Quantum secure direct communication with quantum encryption based on pure entangled states

Li Xi-Han, Li Chun-Yan, Deng Fu-Guo, Zhou Ping, Liang Yu-Jie, Zhou Hong-Yu
Chin. Phys., 2007, 16 (8): 2149-2153 doi: 10.1088/1009-1963/16/8/001
Full Text: [PDF 113 KB] (Downloads:1084)
Show Abstract
This paper presents a scheme for quantum secure direct communication with quantum encryption. The two authorized users use repeatedly a sequence of the pure entangled pairs (quantum key) shared for encrypting and decrypting the secret message carried by the travelling photons directly. For checking eavesdropping, the two parties perform the single-photon measurements on some decoy particles before each round. This scheme has the advantage that the pure entangled quantum signal source is feasible at present and any eavesdropper cannot steal the message.

Unified symmetry of Vacco dynamical systems

Li Yuan-Cheng, Jing Hong-Xing, Xia Li-Li, Wang Jing, Hou Qi-Bao
Chin. Phys., 2007, 16 (8): 2154-2158 doi: 10.1088/1009-1963/16/8/002
Full Text: [PDF 101 KB] (Downloads:519)
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Based on the total time derivative along the trajectory of the time, we study the unified symmetry of Vacco dynamical systems. The definition and the criterion of the unified symmetry for the system are given. Three kinds of conserved quantities, i.e. the Noether conserved quantity, the generalized Hojman conserved quantity and the Mei conserved quantity, are deduced from the unified symmetry. An example is presented to illustrate the results.

Discrete doubly periodic and solitary wave solutions for the semi-discrete coupled mKdV equations

Wu Xiao-Fei, Zhu Jia-Min, Ma Zheng-Yi
Chin. Phys., 2007, 16 (8): 2159-2166 doi: 10.1088/1009-1963/16/8/003
Full Text: [PDF 127 KB] (Downloads:552)
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In this paper, the improved Jacobian elliptic function expansion approach is extended and applied to constructing discrete solutions of the semi-discrete coupled modified Korteweg de Vries (mKdV) equations with the aid of the symbolic computation system Maple. Some new discrete Jacobian doubly periodic solutions are obtained. When the modulus $m \rightarrow 1$, these doubly periodic solutions degenerate into the corresponding solitary wave solutions, including kink-type, bell-type and other types of excitations.

Study on an extended Boussinesq equation

Chen Chun-Li, Zhang Jin E, Li Yi-Shen
Chin. Phys., 2007, 16 (8): 2167-2179 doi: 10.1088/1009-1963/16/8/004
Full Text: [PDF 161 KB] (Downloads:500)
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An extended Boussinesq equation that models weakly nonlinear and weakly dispersive waves on a uniform layer of water is studied in this paper. The results show that the equation is not Painlev\'e-integrable in general. Some particular exact travelling wave solutions are obtained by using a function expansion method. An approximate solitary wave solution with physical significance is obtained by using a perturbation method. We find that the extended Boussinesq equation with a depth parameter of $1/\sqrt 2$ is able to match the Laitone's (1960) second order solitary wave solution of the Euler equations.

The acoustoelastic effect on Rayleigh waves in elastic--plastic deformed layered rocks

Liu Jin-Xia, Cui Zhi-Wen, Wang Ke-Xie
Chin. Phys., 2007, 16 (8): 2180-2187 doi: 10.1088/1009-1963/16/8/005
Full Text: [PDF 265 KB] (Downloads:519)
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On the basis of the acoustoelastic theory for elastic--plastic materials, the influence of statically deformed states including both the elastic and plastic deformations induced by applied uniaxial stresses on the Rayleigh wave in layered rocks is investigated by using a transfer matrix method. The acoustoelastic effects of elastic--plastic strains in rocks caused by static deformations, are discussed in detail. The Rayleigh-type and Sezawa modes exhibit similar trends in acoustoelastic effect: the acoustoelastic effect increasing rapidly with the frequency-thickness product and the phase velocity change approaching a constant value for thick layer and high frequency limit. Elastic--plastic deformations in the Castlegate layered rock obviously modify the phase velocity of the Rayleigh wave and the cutoff points for the Sezawa modes. The investigation may be useful for seismic exploration, geotechnical engineering and ultrasonic detection.

Entanglement-enhanced classical communication through an amplitude-damping channel

Hou Li-Zhen, Fang Mao-Fa
Chin. Phys., 2007, 16 (8): 2188-2193 doi: 10.1088/1009-1963/16/8/006
Full Text: [PDF 110 KB] (Downloads:470)
Show Abstract
We consider the problem of trying to send a single classical bit through an amplitude-damping channel when two transmissions through the channel are available as a resource. It is demonstrated that two entangled transmissions can enhance the receiver's capability of making a correct inference under certain conditions compared with two product-state transmissions.

A controlled quantum teleportation scheme of an N-particle unknown state via three-particle W1 states

Xiu Xiao-Ming, Dong Li, Gao Ya-Jun, Chi Feng
Chin. Phys., 2007, 16 (8): 2194-2199 doi: 10.1088/1009-1963/16/8/007
Full Text: [PDF 235 KB] (Downloads:419)
Show Abstract
In this paper a controlled quantum teleportation scheme of an N-particle unknown state is proposed when N groups of three-particle W1 states are utilized as quantum channels. The quantum information of N-particle unknown state is transmitted from the sender to the recipient under the control of all supervisors. It can be realized with a certain probability. After the sender makes Bell-state measurements and the supervisors perform the computational basis measurements, the recipient will introduce auxiliary particles and carry out unitary transformations depending on classical information from the sender and the supervisors. Finally, the computational basis measurement will be performed by the recipient to confirm whether the teleportation succeeds or not. The successful completion of the scheme relies on all supervisors' cooperation. In addition, the fidelity and security of the scheme are discussed.

Application of three-mode Einstein-Podolsky-Rosen entangled state with continuous variables to teleportation

Hu Li-Yun, Lu Hai-Liang
Chin. Phys., 2007, 16 (8): 2200-2210 doi: 10.1088/1009-1963/16/8/008
Full Text: [PDF 158 KB] (Downloads:578)
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We consider how to teleport two- and three-mode Einstein--Podolsky--Rosen entangled states (|\eta> and | pt,\chi2,\chi3>) via a | pt,\chi2,\chi3> quantum channel for continuous variables. Using the complete and orthogonal representation of the entangled states, we can not only find the a complete basis set for the joint measurement but also propose the specific scheme of teleportation. Our calculation can be greatly simplified by using their Schmidt decompositions.

A simple scheme for generating multi-atom GHZ state via cavity QED

Wang Jun, Yu Long-Bao, Ye Liu
Chin. Phys., 2007, 16 (8): 2211-2214 doi: 10.1088/1009-1963/16/8/009
Full Text: [PDF 95 KB] (Downloads:540)
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This paper proposes a simple scheme for generating a three-atom GHZ state via cavity quantum electrodynamics (QED). The task can be achieved through the interaction between two EPR states, which can be prepared easily with current technology. In this scheme, the cavity field is only virtually excited during the interaction process, and no quantum information transfer between the atoms and the cavity is required. Thus it greatly prolongs the efficient decoherent time. Moreover, this scheme is also applicable for generating an N-atom GHZ state.

An efficient quantum key distribution protocol with orthogonal product states

Yang Yu-Guang, Wen Qiao-Yan
Chin. Phys., 2007, 16 (8): 2215-2218 doi: 10.1088/1009-1963/16/8/010
Full Text: [PDF 99 KB] (Downloads:504)
Show Abstract
An efficient quantum key distribution (QKD) protocol with orthogonal product states in the 3 \otimes 3 Hilbert space is presented. The sender, Alice, disorders the orthogonal product state sequence and sends it to Bob. After Alice has published the matching information of the particle sequence, Bob recovers the correct correspondences and makes an orthogonal measurement on the orthogonal product states to obtain the information sent by Alice. Finally, security analysis is also made.

Cluster states prepared by using hot trapped ions

Yang Rong-Can, Li Hong-Cai, Lin Xiu, Huang Zhi-Ping
Chin. Phys., 2007, 16 (8): 2219-2223 doi: 10.1088/1009-1963/16/8/011
Full Text: [PDF 112 KB] (Downloads:538)
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We propose a scheme for the preparation of one-dimensional and two-dimensional cluster states by using hot trapped ions. The scheme is based on the interaction between two ions and bichromatic radiation. The vibrational mode in our protocol is only virtually excited so that the system is insensitive to the thermal field. In addition, we only use two levels of ions as qubits and the successful probability may achieve 100%.

Feasible schemes for preparing all five-photon graph states

Zhang Jin, Zhou Xiao-Qi, Yang Tao
Chin. Phys., 2007, 16 (8): 2224-2228 doi: 10.1088/1009-1963/16/8/012
Full Text: [PDF 417 KB] (Downloads:519)
Show Abstract
We propose feasible experimental schemes for preparing all five-photon graph states. Our schemes require only linear optical elements, photon detectors and post-selection, which are available in current experiment so that these schemes are within the reach of the current technology.

Entanglement in an anisotropic spin-1 Heisenberg chain

Zhu Yan, Zhu Shi-Qun, Hao Xiang
Chin. Phys., 2007, 16 (8): 2229-2236 doi: 10.1088/1009-1963/16/8/013
Full Text: [PDF 1394 KB] (Downloads:635)
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The entanglement in an anisotropic spin-1 Heisenberg chain with a uniform magnetic field is investigated. The ground-state entanglement will undergo two different kinds of transitions when the anisotropy \Delta and the amplitude of the magnetic field B are varied. The thermal entanglement of the nearest neighbour always declines when B increases no matter what the value of the anisotropy is. It is very interesting to note that the entanglement of the next-nearest neighbour can increase to a maximum at a certain magnetic field. Regardless of the boundary condition, the nearest-neighbour entanglement always decreases and approaches to a constant value when the size of the system is very large. The constant value of open boundary condition is much larger than that of periodic boundary condition.

The separability of two-mode Gaussian state under amplification and symmetric damping

Chen Xiao-Yu, Jiang Li-Zhen, Wu Liang-Neng
Chin. Phys., 2007, 16 (8): 2237-2243 doi: 10.1088/1009-1963/16/8/014
Full Text: [PDF 442 KB] (Downloads:344)
Show Abstract
The performances of a two-mode Gaussian state under parametric amplification, symmetric amplitude damping and thermal noise are studied. The time-dependent complex correlation matrix of the state in evolution is given. The separability of the final two-mode Gaussian state is examined under symmetric amplification and asymmetric amplification separately.

Generation and control of chaos in a Bose--Einstein condensate

Xu Jun, Hai Wen-Hua, Li Hui
Chin. Phys., 2007, 16 (8): 2244-2253 doi: 10.1088/1009-1963/16/8/015
Full Text: [PDF 1038 KB] (Downloads:827)
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For a Bose--Einstein condensate (BEC) confined in a double lattice consisting of two weak laser standing waves we find the Melnikov chaotic solution and chaotic region of parameter space by using the direct perturbation method. In the chaotic region, spatial evolutions of the chaotic solution and the corresponding distribution of particle number density are bounded but unpredictable between their superior and inferior limits. It is illustrated that when the relation k1\approx k2 between the two laser wave vectors is kept, the adjustment from k21 to k2\ge k1 can transform the chaotic region into regular one or the other way round. This suggests a feasible scheme for generating and controlling chaos, which could lead to an experimental observation in the near future.

Application of periodic orbit theory in chaos-based security analysis

Long Min, Qiu Shui-Sheng
Chin. Phys., 2007, 16 (8): 2254-2258 doi: 10.1088/1009-1963/16/8/016
Full Text: [PDF 1341 KB] (Downloads:756)
Show Abstract
Chaos-based encryption schemes have been studied extensively, while the security analysis methods for them are still problems to be resolved. Based on the periodic orbit theory, this paper proposes a novel security analysis method. The periodic orbits theory indicates that the fundamental frequency of the spiraling orbits is the natural frequency of associated linearized system, which is decided by the parameters of the chaotic system. Thus, it is possible to recover the plaintext of secure communication systems based on chaotic shift keying by getting the average time on the spiraling orbits. Analysis and simulation results show that the security analysis method can break chaos shift keying secure communication systems, which use the parameters as keys.

Controlling a time-delay system using multiple delay feedback control

Qi Wei, Zhang Yan, Wang Ying-Hai
Chin. Phys., 2007, 16 (8): 2259-2263 doi: 10.1088/1009-1963/16/8/017
Full Text: [PDF 1156 KB] (Downloads:997)
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In this paper multiple delay feedback control (MDFC) with different and independent delay times is shown to be an efficient method for stabilizing fixed points in finite-dimensional dynamical systems. Whether MDFC can be applied to infinite-dimensional systems has been an open question. In this paper we find that for infinite-dimensional systems modelled by delay differential equations, MDFC works well for stabilizing (unstable) steady states in long-, moderate- and short-time delay regions, in particular for the hyperchaotic case.

Continuous feedback control of KdV Burgers system

Zhang Li-Ping, Xue Ju-Kui
Chin. Phys., 2007, 16 (8): 2264-2271 doi: 10.1088/1009-1963/16/8/018
Full Text: [PDF 1467 KB] (Downloads:649)
Show Abstract
The chaos in the KdV Burgers equation describing a ferroelectric system has been successfully controlled by using a continuous feedback control. This system has two stationary points. In order to know whether the chaos is controlled or not, the instability of control equation has been analysed numerically. The numerical analysis shows that the chaos can be converted to one point by using one control signal, however, it can converted to the other point by using three control signals. The chaotic motion is converted to two desired stationary points and periodic orbits in numerical experiment separately.

Impulsive control of chaotic systems with exogenous perturbations

Liu Xing-Wen, Huang Qin-Zhen, Gao Xin, Shao Shi-Quan
Chin. Phys., 2007, 16 (8): 2272-2277 doi: 10.1088/1009-1963/16/8/019
Full Text: [PDF 330 KB] (Downloads:696)
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The impulsive control of chaotic systems, which are subjected to unbounded exogenous perturbations, is considered. By using the theory of impulsive differential equation together with the fuzzy control technique, the authors propose an impulsive robust chaos controlling criterion expressed as linear matrix inequalities (LMIs). Based on the proposed control criterion, the procedure for designing impulsive controllers of common (perturbed) chaotic systems is provided. Finally, a numerical example is given to demonstrate the obtained theoretical result.

Analysis and implementation of a new hyperchaotic system

Wang Guang-Yi, Liu Jing-Biao, Zheng Xin
Chin. Phys., 2007, 16 (8): 2278-2284 doi: 10.1088/1009-1963/16/8/020
Full Text: [PDF 3031 KB] (Downloads:1022)
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Based on a modified Lorenz system, a relatively simple four-dimensional continuous autonomous hyperchaotic system is proposed by introducing a state feedback controller. The system consists of four coupled first-order ordinary differential equations with three nonlinear cross-product terms. Some dynamical properties of this hyperchaotic system, including equlibria, stability, Lyapunov exponent spectrum and bifurcation, are analysed in detail. Moreover, an electronic circuit diagram is designed for demonstrating the existence of the hyperchaos, and verifying computer simulation results.

Nonchaotic random behaviour in the second order autonomous system

Xu Yun, Zhang Jian-Xia, Xu Xia, Zhou Hong
Chin. Phys., 2007, 16 (8): 2285-2290 doi: 10.1088/1009-1963/16/8/021
Full Text: [PDF 615 KB] (Downloads:548)
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Evidence is presented for the nonchaotic random behaviour in a second-order autonomous deterministic system. This behaviour is different from chaos and strange nonchaotic attractor. The nonchaotic random behaviour is very sensitive to the initial conditions. Slight difference of the initial conditions will generate wholly different phase trajectories. This random behaviour has a transient random nature and is very similar to the coin-throwing case in the classical theory of probability. The existence of the nonchaotic random behaviour not only can be derived from the theoretical analysis, but also is proved by the results of the simulated experiments in this paper.

Noise-induced striped trajectories of Rossler systems

Huang Zhi-Hua, Dong Ya-Li
Chin. Phys., 2007, 16 (8): 2291-2295 doi: 10.1088/1009-1963/16/8/022
Full Text: [PDF 1477 KB] (Downloads:405)
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In this paper, the generation of striped trajectories in phase space by noise-injection is considered. With suitable amplitudes of noise, the steady-state system orbits appear in rectangular striped shape. The relationship between the shape (including the range and the number of stripes) and some parameters is discussed. The result shows that noise can also generate the striped shape effectively and simply, which is similar to the newly-discovered striped pattern generated by controlled Rossler systems.

Density functional theory for molecular orientation of hard rod fluids in hard slits

Cao Da-Peng, Cheng Li-Sheng, Wang Wen-Chuan
Chin. Phys., 2007, 16 (8): 2296-2303 doi: 10.1088/1009-1963/16/8/023
Full Text: [PDF 631 KB] (Downloads:577)
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A density functional theory (DFT) is used to investigate molecular orientation of hard rod fluids in a hard slit. The DFT approach combines a modified fundamental measure theory (MFMT) for excluded-volume effect with the first order thermodynamics perturbation theory for chain connectivity. In the DFT approach, the intra-molecular bonding orientation function is introduced. We consider the effects of molecular length (i.e. aspect ratio of rod) and packing fraction on the orientations of hard rod fluids and flexible chains. For the flexible chains, the chain length has no significant effect while the packing fraction shows slight effect on the molecular orientation distribution. In contrast, for the hard rod fluids, the chain length determines the molecular orientation distribution, while the packing fraction has no significant effect on the molecular orientation distribution. By making a comparison between molecular orientations of the flexible chain and the hard rod fluid, we find that the molecular stiffness distinctly affects the molecular orientation. In addition, partitioning coefficient indicates that the longer rodlike molecule is more difficult to enter the confined phase, especially at low bulk packing fractions.

Detecting and describing the modular structures of weighted networks

Li Ke-Ping, Gao Zi-You
Chin. Phys., 2007, 16 (8): 2304-2309 doi: 10.1088/1009-1963/16/8/024
Full Text: [PDF 567 KB] (Downloads:516)
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In the functional properties of complex networks, modules play a central role. In this paper, we propose a new method to detect and describe the modular structures of weighted networks. In order to test the proposed method, as an example, we use our method to analyse the structural properties of the Chinese railway network. Here, the stations are regarded as the nodes and the track sections are regarded as the links. Rigorous analysis of the existing data shows that using the proposed algorithm, the nodes of network can be classified naturally. Moreover, there are several core nodes in each module. Remarkably, we introduce the correlation function $G_{rs}$, and use it to distinguish the different modules in weighted networks.

Electronic structure and defect states of transition films from amorphous to microcrystalline silicon studied by surface photovoltage spectroscopy

Yu Wei, Wang Chun-Sheng, Lu Wan-Bing, He Jie, Han Xiao-Xia, Fu Guang-Sheng
Chin. Phys., 2007, 16 (8): 2310-2314 doi: 10.1088/1009-1963/16/8/025
Full Text: [PDF 621 KB] (Downloads:479)
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In this paper, surface photovoltage spectroscopy (SPS) is used to determine the electronic structure of the hydrogenated transition Si films. All samples are prepared by using helicon wave plasma-enhanced chemical vapour deposition technique, the films exhibit a transition from the amorphous phase to the microcrystalline phase with increasing temperature. The film deposited at lower substrate temperature has the amorphous-like electronic structure with two types of dominant defect states corresponding to the occupied Si dangling bond states (D0/D- and the empty Si dangling states (D+). At higher substrate temperature, the crystallinity of the deposited films increases, while their band gap energy decreases. Meanwhile, two types of additional defect states is incorporate into the films as compared with the amorphous counterpart, which is attributed to the interface defect states between the microcrystalline Si grains and the amorphous matrix. The relative SPS intensity of these two kinds of defect states in samples deposited above 300\du increases first and decreases afterwards, which may be interpreted as a result of the competition between hydrogen release and crystalline grain size increment with increasing substrate temperature.

The non-destructive threshold of the graphite surface by STM in the ultra-fast pulse mode

Xu Chun-Kai, Wei Zheng, Chen Xiang-Jun, Xu Ke-Zun
Chin. Phys., 2007, 16 (8): 2315-2318 doi: 10.1088/1009-1963/16/8/026
Full Text: [PDF 705 KB] (Downloads:401)
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In this paper single ultra-fast voltage pulses are introduced to the Pt/Ir tip of a scanning tunnelling microscope (STM), and the non-destructive threshold of the graphite surface is studied systematically in a wide range of pulse durations (from 10$^{4}$ to 8\,ns). Considering the waveform distortion of the pulses at the tunnelling region, this paper gives the corrected threshold curve of pulse amplitude depending on pulse duration. A new explanation of threshold power has been suggested and fits the experimental results well.

Influence of tube voltage and current on in-line phase contrast imaging using a microfocus x-ray source

Li Chen, Li Zheng, Yu Ai-Min, Li Cheng-Quan
Chin. Phys., 2007, 16 (8): 2319-2324 doi: 10.1088/1009-1963/16/8/027
Full Text: [PDF 708 KB] (Downloads:487)
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In-line x-ray phase contrast imaging has attracted much attention due to two major advantages: its effectiveness in imaging weakly absorbing materials, and the simplicity of its facilities. In this paper a comprehensive theory based on Wigner distribution developed by Wu and Liu [Med. Phys. 31 2378-2384 (2004)] is reviewed. The influence of x-ray source and detector on the image is discussed. Experiments using a microfocus x-ray source and a CCD detector are conducted, which show the role of two key factors on imaging: the tube voltage and tube current. High tube current and moderate tube voltage are suggested for imaging.
NUCLEAR PHYSICS

Optimal reactions for synthesis of nuclides of element 108

Liu Zu-Hua, Zhou Hong-Yu
Chin. Phys., 2007, 16 (8): 2338-2342 doi: 10.1088/1009-1963/16/8/030
Full Text: [PDF 451 KB] (Downloads:385)
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The cross sections for the production of nuclides of element 108 via hot fusion evaporation reactions are studied using a two-parameter Smoluchowski equation. The optimal reactions for the synthesis of new nuclides of element 108 with mass numbers from 266 to 271 are suggested. The macroscopic-microscopic approach predicts a strong deformed shell closure at Z \approx 108 and N=162. The synthesis of more nuclides of element 108 is meaningful to the confirmation of the existence of this deformed shell closure.

International Linear Collider damping ring lattice design with two wiggler sections

Sun Yi-Peng, Gao Jie, Guo Zhi-Yu
Chin. Phys., 2007, 16 (8): 2343-2348 doi: 10.1088/1009-1963/16/8/031
Full Text: [PDF 1238 KB] (Downloads:331)
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The International Linear Collider (ILC), which is based on super-conducting RF acceleration technology, requires the damping rings to provide beams with extremely small equilibrium emittance, and large acceptance to ensure good injection efficiency for high-emittance, and high-energy spread beam from the positron source. In order to reduce the cost for ILC damping rings, an alternative lattice which is different from the baseline configuration design has been designed with modified FODO arc cells, and the total quadrupole number has been reduced by half. At the same time, to decrease the total cost involved in constructing access shafts needed to supply power, cryogenics etc. for the wigglers and other systems, the number of wiggler sections is decreased from 8 to 4, and further to 2. This new lattice has been optimized to have a good dynamic aperture. This alternative ILC damping ring lattice design will reduce the cost largely as compared with the baseline design.
CLASSICAL AREAS OF PHENOMENOLOGY

Effect of spontaneously generated coherence on inversionless lasing gain in an atomic system with Doppler broadening

Ma Hui, Tan Xia, Tian Shu-Fen, Tong Dian-Min, Fan Xi-Jun
Chin. Phys., 2007, 16 (8): 2400-2406 doi: 10.1088/1009-1963/16/8/041
Full Text: [PDF 186 KB] (Downloads:462)
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We have studied the effect of the spontaneously generated coherence (SGC) on gain of lasing without inversion (LWI) in a closed three-level $\Lambda $-type atomic system with Doppler broadening. It is shown that, regardless of the driving and probe fields being co- or counter-propagating, at a suitable value of the Doppler width, we can obtain a much larger LWI gain with SGC than that without SGC; and the region of the LWI gain spectrum with SGC is obviously larger than that without SGC. When the Doppler width takes a constant value, the gain does not monotonically decrease or increase with increasing strength of SGC, the largest LWI gain can be obtained by adjusting strength of SGC. Generally speaking, the co-propagating probe and driving fields is favourable to obtain a larger LWI gain.

Atomic coherence control on the entanglement of two atoms in two-photon processes

Hu Yao-Hua, Fang Mao-Fa, Wu Qin
Chin. Phys., 2007, 16 (8): 2407-2414 doi: 10.1088/1009-1963/16/8/042
Full Text: [PDF 213 KB] (Downloads:510)
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Considering two identical two-level atoms interacting with a single-mode thermal field through two-photon processes, this paper studies the atomic coherence control on the entanglement between two two-level atoms, and finds that the entanglement is greatly enhanced due to the initial atomic coherence. The results show that the entanglement can be manipulated by changing the initial parameters of the system, such as the superposition coefficients and the relative phases of the initial atomic coherent state and the mean photon number of the cavity field.

Wigner function and tomogram of the Hermite polynomial state

Meng Xiang-Guo, Wang Ji-Suo, Li Yan-Ling
Chin. Phys., 2007, 16 (8): 2415-2421 doi: 10.1088/1009-1963/16/8/043
Full Text: [PDF 540 KB] (Downloads:455)
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Using the coherent state representation of Wigner operator and the technique of integration within an ordered product (IWOP) of operators, this paper derives the Wigner function for the Hermite polynomial state (HPS). The tomogram of the HPS is calculated with the aid of newly introduced intermediate coordinate-momentum representation in quantum optics.

The nonlinear squeezed one-photon states and their nonclassical properties

Wang Ji-Suo, Meng Xiang-Guo
Chin. Phys., 2007, 16 (8): 2422-2427 doi: 10.1088/1009-1963/16/8/044
Full Text: [PDF 213 KB] (Downloads:398)
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By virtue of the technique of integration within an ordered product (IWOP) of operators and the properties of the inverses of annihilation and creation operators of f-oscillator, this paper obtains two new types of squeezed operators and f-analogues of squeezed one-photon states, which are quite different from ones constructed by Song and Fan ({Phys. Lett.} A {294} (2002) 66). Subsequently, some nonclassical properties of the states are investigated in detail.

The spatial properties of atomic Raman--Nath diffraction

Li Li-Ping, Zhang Li-Yan, Song Pei-Jun, Xie Xiao-Tao, Li Wei-Bin
Chin. Phys., 2007, 16 (8): 2428-2432 doi: 10.1088/1009-1963/16/8/045
Full Text: [PDF 1156 KB] (Downloads:378)
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This paper obtains the exact analytical solution of atomic Raman--Nath diffraction in the coordinate representation and discusses the influence of different initial conditions and detunings on the atomic spatial population distribution. The phase difference between the dipole matrix element and initial atomic population may influence the atomic spatial population distribution after diffraction, which has never been discussed before as far as we know. It offers a method to measure the phase by the spatial population distribution, which is interesting in the study of quantum optics.

Theoretical research on enhancement of gain for Ni-like Ag 13.9nm x-ray laser using a new two-layer target

Zhang Guo-Ping, Zhang Tan-Xin, Zheng Wu-Di, Qiao Xiu-Mei
Chin. Phys., 2007, 16 (8): 2433-2438 doi: 10.1088/1009-1963/16/8/046
Full Text: [PDF 232 KB] (Downloads:372)
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For experiments such as on Ni-like Ag x-ray laser, driven by 1\omega laser, the gain region is only several~nm depth near the target surface, this paper proposes a new two-layer target, in which a thin layer (several nm depth) of silver is plated on the surface of some other materials. Furthermore, the Ni-like Ag 13.9~nm x-ray laser produced by three new kinds of two-layer target with CH, Al and Ge as foundation, was theoretically studied.

2D hydrodynamic simulation of a line-focused plasma in Ni-like Ag x-ray laser research

Zheng Wu-Di, Zhang Guo-Ping
Chin. Phys., 2007, 16 (8): 2439-2443 doi: 10.1088/1009-1963/16/8/047
Full Text: [PDF 1191 KB] (Downloads:552)
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In most collisional schemes of x-ray laser (XRL) experiments, a bow-like intensity distribution of XRL is often observed, and it is generally ascribed to the two-dimensional hydrodynamic behaviour of expanding plasma. In order to better understand its essence in physics, a newly developed two-dimensional non-equilibrium radiation hydrodynamic code XRL2D is used to simulate a quasi-steady state Ni-like Ag XRL experiment on ShenGuang-II facility. The simulation results show that the bow-like distribution of Ni-like ions caused by over-ionization in the central area of plasma is responsible for the bow-like shape of the XRL intensity distribution observed.

Lattice Boltzmann simulations of a dumbbell moving in a Poiseuille flow

Yi Hou-Hui, Chen Yan-Yan, Li Hua-Bing
Chin. Phys., 2007, 16 (8): 2444-2448 doi: 10.1088/1009-1963/16/8/048
Full Text: [PDF 151 KB] (Downloads:382)
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In this paper, the lattice Boltzmann method is applied to simulate a dumbbell moving in a pressure-driven flow in a planar channel with the stress-integration method for the evaluation of hydrodynamic force acting on the cylinders. The simulation results show that the dumbbell also has the important feature of the Segr\'e--Silberberg effect like a particle in a Poiseuille flow. The dumbbell trajectories, orientations, the cylinders vertical velocities and angular velocities all reach their equilibrium values separately independent of their initial positions. It is also found that the dumbbell equilibrium positions depend on the flow Reynolds number, blockage ratio and elastic coefficient. This study is expected to be helpful to understand the dynamics of polymer solutions, polymer synthesis and reaction, etc.
ATOMIC AND MOLECULAR PHYSICS

Laser pulse design for coherent laser control of potassium atoms

Zhang Xian-Zhou, Jia Guang-Rui, He Hai-Fang
Chin. Phys., 2007, 16 (8): 2349-2355 doi: 10.1088/1009-1963/16/8/032
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In this paper, the dynamics of coherent laser control of potassium atoms is studied by using the time-dependent multilevel approach (TDMA). The calculation results of population transfer are presented with different laser fields. The results show that the population can be transferred to target state completely by a specially designed laser field.

The molecular structure and the analytical potential energy function of S2- and S3-

Liu Yu-Fang, Li Jun-Yu, Han Xiao-Qin, Sun Jin-Feng
Chin. Phys., 2007, 16 (8): 2356-2360 doi: 10.1088/1009-1963/16/8/033
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In this paper, the equilibrium geometry, harmonic frequency and dissociation energy of S2- and S3- have been calculated at QCISD/6-311++G(3d2f) and B3P86/6-311++G(3d2f) level. The{ }S2- ground state is of -Pig, the S3- ground state is of -B1 and S3- has a bent (C2V) structure with an angle of 115.65℃ The results are in good agreement with these reported in other literature. For S3- ion, the vibration frequencies and the force constants have also been calculated. Base on the general principles of microscopic reversibility, the dissociation limits has been deduced. The Murrell--Sorbie potential energy function for S2- has been derived according to the ab initio data through the least-squares fitting. The force constants and spectroscopic data for S2- have been calculated, then compared with other theoretical data. The analytical potential energy function of S3- have been obtained based on the many-body expansion theory. The structure and energy can correctly reappear on the potential surface.

K-shell photoionization of boron-like carbon ions: analysis of 1s-2p resonances

Wang Guo-Li, Zhou Xiao-Xin
Chin. Phys., 2007, 16 (8): 2361-2366 doi: 10.1088/1009-1963/16/8/034
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Close-coupling calculations based on an R-matrix formalism are performed for the 1s--2p resonance photoionizations from the low-lying states of boron-like carbon ions. The resonance energies, widths and oscillator strengths of 1s-2p core excitations are determined by analysing the calculated photoionization cross sections. Our calculations are in reasonable agreement with the experimental and theoretical results presented by other authors. The present numerical values may help to analyse the astrophysical and laboratory plasmas.

Calculation of the elastic scattering properties for cold and ultracold 39K atoms in a triplet state

Hu Qiu-Bo, Wang Xiao-Fei, Sun Jin-Feng, Zhu Zun-Lue
Chin. Phys., 2007, 16 (8): 2367-2370 doi: 10.1088/1009-1963/16/8/035
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The elastic scattering properties for collisions between cold and ultracold 39K atoms in a triplet state are investigated. Based on the recent theoretical and experimental results, the improved hybrid potential is presented for a triplet a3\Sigmau+ ground state of K2. Our calculated value of the s-wave scattering length a by using the Numerov method for the triplet state is 79.578a0 and found to be in good agreement with the previous ones. The numbers of bound states are supported by the molecular potential. Pronounced shape resonances appear for the l = 3 partial waves for the a3\Sigmau+ state. Furthermore, the s-wave scattering cross section, the total cross section and energy positions of shape resonances for the a3\Sigmau+ state are calculated.

Ab initio calculation on accurate analytic potential energy functions and harmonic frequencies of c3+g and B1u states of dimer 7Li2

Yu Ben-Hai, Shi De-Heng, Sun Jin-Feng, Zhu Zun-Lue, Liu Yu-Fang, Yang Xiang-Dong
Chin. Phys., 2007, 16 (8): 2371-2377 doi: 10.1088/1009-1963/16/8/036
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The comparison between single-point energy scanning (SPES) and geometry optimization (OPT) in determining the equilibrium geometries of c3\Sigma+g and B1u states of dimer 7Li2 is made at numerous basis sets by using a symmetry-adapted-cluster configuration-interaction (SAC-CI) method in the Gaussian 03 program package. In this paper the difference of the equilibrium geometries obtained by SPES and by OPT is reported. The results obtained by SPES are found to be more reasonable than those obtained by OPT in full active space at the present SAC-CI level of theory. And the conclusion is attained that the cc-PVTZ is a most suitable basis set for these states. The calculated dissociation energies and equilibrium geometries are 0.8818 eV and 0.3090 nm for c3\Sigma+g state, and 0.3668 eV and 0.2932 nm for B1u state respectively. The potential energy curves are calculated over a wide internuclear distance range from about 2.5a0 to 37a0 and have a least-squares fit into the Murrell--Sorbie function. According to the calculated analytic potential energy functions, the harmonic frequencies (\omegae and other spectroscopic data (\omegae \chie , \Be and \alphae are calculated. Comparison of the theoretical determinations at present work with the experiments and other theories clearly shows that the present work is the most complete effort and thus represents an improvement over previous theoretical results.

Multiple ionization of argon accompanied by electron loss and capture of 0.22--6.35 MeV Cq+ ions

Chen Lin, Chen Xi-Meng, Shao Jian-Xiong, Lu Yan-Xia, Ding Bao-Wei, Cui Ying, Gao Zhi-Min, Liu Yu-Wen, Du Juan, Xie Jiang-Shan, Sun Guang-Zhi, Liu Zhao-Yuan
Chin. Phys., 2007, 16 (8): 2378-2383 doi: 10.1088/1009-1963/16/8/037
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In this paper a projectile ions--recoil ions coincidence technique is employed to investigate the target ionization and projectile charge state changing processes in the collision of 0.22--6.35 MeVCq+(q = 1-4) ions with argon atoms. The partial cross section ratios of the double, triple, quadruplicate ionization to the single ionization (or the single capture) of argon associated with single electron loss (or single electron capture) by the projectile are measured and compared with the previous experimental results. In the present experiment, it is observed that the ratios of ionization cross sections R associated with single loss and single capture depend strongly on the projectile charge state and vary significantly with different reaction channels as impact energy increases. In addition, this paper gets empirical scaling laws for the ionization cross section ratios R corresponding to the projectile single loss and finds that the ratios of the double ionization to the single ionization associated with single electron capture remain constant in the present energy range.

Production of recoil ions Hei+ accompanied by single electron loss of 0.2--7MeV Cq+ and 0.25--5MeV Oq+ (q=1--4) ions

Chen Xi-Meng, Lu Yan-Xia, Ding Bao-Wei, Liu Yu-Wen, Cui Ying, Gao Zhi-Min, Fu Hong-Bin, Du Juan, Shao Jian-Xiong
Chin. Phys., 2007, 16 (8): 2384-2388 doi: 10.1088/1009-1963/16/8/038
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Target ionization accompanied with projectile electron loss is investigated for 0.2--7 MeV Cq+(q=1-4) with He and 0.25--5 MeV Oq+(q=1-4) with He collisions. For projectile single-electron loss channel, the He double-to-single ionization ratio R is nearly independent of projectile charge state but dependent on the nuclear charge of projectile Zp. The results are analysed with atomic structure qualitatively. So far there have not existed the experimental data comparable with our results, to our knowledge. The ratio $R$ is interpreted in terms of the two-step mechanism. This analysis agrees well with similar experiments in the literature.

Calculations on the hyperfine constants of the ground states for lithium-like system

Wu Xiao-Li, Yu Kai-Zhi, Gou Bing-Cong, Zhang Meng
Chin. Phys., 2007, 16 (8): 2389-2393 doi: 10.1088/1009-1963/16/8/039
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In this paper a relativistic many-body perturbation calculation is performed to calculate the hyperfine constants of the ground states for lithium-like isoelectronic sequence. Zeroth-order hyperfine constants are calculated with Dirac--Fock wavefunctions, and the finite basis sets of the Dirac--Fock equations are constructed by B splines. With the finite basis sets, the core polarization and the correlation effect are evaluated.

DFT study on the structure and spectra of Ga5P5 cluster

Zhang Cai-Rong, Chen Hong-Shan, Song Yan, Xu Guang-Ji
Chin. Phys., 2007, 16 (8): 2394-2399 doi: 10.1088/1009-1963/16/8/040
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In this paper, possible structures of Ga5P5 cluster were optimized by using density functional method with generalized gradient correction (B3LYP). The electronic structure of the isomers with lower energy was studied. The most stable structure obtained for Ga5P5 is a distorted pentaprism. The Ga-P bond formed in the cluster is strongly ionic. Based on NBO analysis, an average value of 0.59 electron transfers from Gallium to Phosphorus. The bond length 2.33--2.43{\AA} is around the value in bulk GaP. The HOMO-LUMO gap is about 2.2 eV. The dipole moment and polarizability are calculated, and the IR and Raman spectra are also presented.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

The solutions of the strongly nonlocal spatial solitons with several types of nonlocal response functions

Ouyang Shi-Gen, Guo Qi, Lan Sheng, Wu Li-Jun
Chin. Phys., 2007, 16 (8): 2325-2330 doi: 10.1088/1009-1963/16/8/028
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The fundamental and second order strongly nonlocal solitons of the nonlocal nonlinear Schr\"{o}dinger equation for several types of nonlocal responses are calculated by Ritz's variational method. For a specific type of nonlocal response, the solutions of the strongly nonlocal solitons with the same beam width but different degrees of nonlocality are identical except for an amplitude factor. For a nonlocal case where the nonlocal response function decays in direct proportion to the $m$th power of the distance near the source point, the power and the phase constant of the strongly nonlocal soliton are in inverse proportion to the $(m+2)$th power of its beam width.

Conservation laws of the generalized nonlocal nonlinear Schr?dinger equation

Ouyang Shi-Gen, Guo Qi, Wu Li-Jun, Lan Sheng
Chin. Phys., 2007, 16 (8): 2331-2337 doi: 10.1088/1009-1963/16/8/029
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The derivations of several conservation laws of the generalized nonlocal nonlinear Schr?dinger equation are presented. These invariants are the number of particles, the momentum, the angular momentum and the Hamiltonian in the quantum mechanical analogy. The Lagrangian is also presented.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Density cavities generated by plasma--field interactions in the far wake region of a space vehicle

Hu Tao-Ping, Luo Qing, Li Xiao-Qing
Chin. Phys., 2007, 16 (8): 2449-2454 doi: 10.1088/1009-1963/16/8/049
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Under the consideration of non-steady case, a set of equations is derived, which describes the non-steady nonlinear interactions between plasma and field in the far wake region of a space vehicle. Numerical calculations are also made and the numerical results show that density cavities and electromagnetic solitary waves are generated due to the modulation instability, if the envelope of high frequency modulation field is strong enough. This is of great significance to the detection of disguised space vehicles.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Dopant diffusion and surface morphology of vanadium implanted 4H-silicon carbide

Wang Chao, Zhang Yi-Men, Zhang Yu-Ming, Ma Ge-Lin, Guo Hui, Xu Da-Qing
Chin. Phys., 2007, 16 (8): 2455-2461 doi: 10.1088/1009-1963/16/8/050
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The diffusion behaviours of vanadium implanted p- and n-type 4H-SiC are investigated by using the secondary ion mass spectrometry (SIMS). Significant redistribution, especially out-diffusion of vanadium towards the sample surface is not observed after 1650℃ annealing for both p- and n-type samples. Atomic force microscopy (AFM) is applied to the characterization of surface morphology, indicating the formation of continuous long furrows running in one direction across the wafer surface after 1650℃ annealing. The surface roughness results from the evaporation and re-deposition of Si species on the surface during annealing. The chemical compositions of sample surface are investigated using x-ray photoelectron spectroscopy (XPS). The results of C 1s and Si 2p core-level spectra are presented in detail to demonstrate the evaporation of Si from the wafer and the deposition of SiO2 on the sample surface during annealing.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Quantum fluctuations of mesoscopic damped double resonance RLC circuit with mutual capacitance--inductance coupling in thermal excitation state

Xu Xing-Lei, Li Hong-Qi, Wang Ji-Suo
Chin. Phys., 2007, 16 (8): 2462-2470 doi: 10.1088/1009-1963/16/8/051
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Based on the scheme of damped harmonic oscillator quantization and thermo-field dynamics (TFD), the quantization of mesoscopic damped double resonance RLC circuit with mutual capacitance--inductance coupling is proposed. The quantum fluctuations of charge and current of each loop in a squeezed vacuum state are studied in the thermal excitation case. It is shown that the fluctuations not only depend on circuit inherent parameters, but also rely on excitation quantum number and squeezing parameter. Moreover, due to the finite environmental temperature and damped resistance, the fluctuations increase with the temperature rising, and decay with time.

Effect of Te doping on superconductivity and charge-density wave in dichalcogenides 2H-NbSe2-xTex (x=0, 0.1, 0.2)

Wang Hong-Tao, Li Lin-Jun, Ye De-Shu, Cheng Xin-Hong, Xu Zhu-An
Chin. Phys., 2007, 16 (8): 2471-2474 doi: 10.1088/1009-1963/16/8/052
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Single crystals of Te-doped dichalcogenides 2H-NbSe2-xTex(x = 0, 0.10, 0.20) were grown by vapour transport method. The effect of Te doping on the superconducting and charge-density wave (CDW) transitions has been investigated. The sharp decrease of residual resistance ratio, RRR = R(300K)/R(8K), with increasing Te content was observed, indicating that the disorder in the conducting plane is induced by Te doping. Meanwhile the superconducting transition temperature, Tc, decreases monotonically with Te content. However, the CDW transition temperature, TCDW, shown by a small jump in the temperature dependence of the resistivity near 30~K, increases slightly. The results show that the suppression of superconductivity might be caused by the enhancement of CDW ordering. The disorder has little influence on the CDW ordering.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Analysis of influence of atmosphere extinction to Raman lidar monitoring CO2 concentration profile

Zhao Pei-Tao, Zhang Yin-Chao, Wang Lian, Zhao Yue-Feng, Su Jia, Fang Xin, Cao Kai-Fa, Xie Jun, Du Xiao-Yong
Chin. Phys., 2007, 16 (8): 2486-2491 doi: 10.1088/1009-1963/16/8/055
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Lidar (Light detection and ranging) system monitoring of the atmosphere is a novel and powerful technique tool. The Raman lidar is well established today as a leading research tool in the study of numerous important areas in the atmospheric sciences. In this paper, the principle of Raman lidar technique measurement CO2 concentration profile is presented and the errors caused by molecular and aerosol extinction for CO2 concentration profile measurement with Raman lidar are also presented. The standard atmosphere extinction profile and `real-time' Hefei area extinction profile are used to conduct correction and the corresponding results are yielded. Simulation results with standard atmosphere mode correction indicate that the errors caused by molecule and aerosol extinction should be counted for the reason that they could reach about 8 ppm and 5~ppm respectively. The relative error caused by Hefei area extinction correction could reach about 6%. The errors caused by the two components extinction influence could produce significant changes for CO2 concentration profile and need to be counted in data processing which could improve the measurement accuracies.
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