Dec 2007, Volume 2 Issue 4

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  • WAN Jin-yin, WANG Yu-zhu, LIU Liang
    In this paper we have reviewed the recent progresses on the ion trapping for quantum information processing and quantum computation. We have first discussed the basic principle of quantum information theory and then focused on ion trapping for quantum information processing. Many variations, especially the techniques of ion chips, have been investigated since the original ion trap quantum computation scheme was proposed. Full two-dimensional control of multiple ions on an ion chip is promising for the realization of scalable ion trap quantum computation and the implementation of quantum networks.
  • TONG Zhao-yang, LIAO Ping, KUANG Le-man
    In this paper, we study single-qubit and single-user quantum repeaters based on CNOT gates under decoherence using the Kraus-operator representations of decoherence. We investigate the influence of decoherence on the information-disturbance trade-off of quantum repeaters. It is found that decoherence may lead to the appearance of three subspaces, called as the normal subspace, the anomalous subspace, and the decoherence-free subspace (DFS), respectively. It is indicated that in the normal subspace decoherence decreases the transmission and estimation fidelities, in the anomalous subspace decoherence enhances these fidelities, and in the DFS these fidelities do not change. The concept of the quality factor is introduced to evaluate the quality of the quantum repeater. It is indicated that the quality factor can be efficiently controlled and manipulated by changing the initial state of the probe qubit. It is found that under certain conditions the quantum repeater can be optimal even in the presence of decoherence.
  • NIU Yue-ping, QIAN Jun, FENG Xun-li, GONG Shang-qing
    In this paper, the recent research on the enhanced Kerr nonlinearity and its application in entangled state discrimination is reported. Two kinds of dynamics, including interacting double dark resonances and spontaneously generated coherence, are presented to enhance the Kerr nonlinearity. The application of Kerr nonlinearity in quantum state discrimination is also discussed. An arbitrary Greenberger-Horne-Zeilinger state can be discriminated using two-photon polarization parity detection which resorts to cross-Kerr nonlinearity between a single-photon qubit and probe field. In addition, a scheme for Greenberger-Horne-Zeilinger state discrimination of matter qubits is also proposed using the dipole induced transparency in a cavity-dipole system.
  • LOU Qi-hong, ZHOU Jun
    In this review article, the development of the double cladding optical fiber for high power fiber lasers is reviewed. The main technology for high power fiber lasers, including laser diode beam shaping, fiber laser pumping techniques, and amplification systems, are discussed in detail. 1050 W CW output and 133 W pulsed output are obtained in Shanghai Institute of Optics and Fine Mechanics, China. Finally, the applications of fiber lasers in industry are also reviewed.
  • LIU Bang-gui, ZHANG Kai-cheng, LI Ying
    The Kinetic Monte Carlo (KMC) method based on the transition-state theory, powerful and famous for simulating atomic epitaxial growth of thin films and nanostructures, was used recently to simulate the nanoferromagnetism and magnetization dynamics of nanomagnets with giant magnetic anisotropy. We present a brief introduction to the KMC method and show how to reformulate it for nanoscale spin systems. Large enough magnetic anisotropy, observed experimentally and shown theoretically in terms of first-principle calculation, is not only essential to stabilize spin orientation but also necessary in making the transition-state barriers during spin reversals for spin KMC simulation. We show two applications of the spin KMC method to monatomic spin chains and spin-polarized-current controlled composite nanomagnets with giant magnetic anisotropy. This spin KMC method can be applied to other anisotropic nanomagnets and composite nanomagnets as long as their magnetic anisotropy energies are large enough.
  • Aditya M. VORA
    The theoretical investigation of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ* , transition temperature Tc, isotope effect exponent α and effective interaction strength N0V of ten CuCZr100-C metallic glasses have been reported using Ashcroft s empty core (EMC) model potential. Three local field correction functions proposed by Hartree (H), Taylor (T) and Ichimaru-Utsumi (IU) are used in the current investigation to study the screening influence on the aforesaid properties. It is observed that the electron-phonon coupling strength λ and the transition temperature Tc are quite sensitive to the selection of the local field correction functions, whereas the Coulomb pseudopotential μ*, isotope effect exponent α and effective interaction strength N0V show weak dependences on local field correction functions. The Tc obtained from IU-local field correction function are found an excellent agreement with available theoretical or experimental data. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in metallic glasses.
  • ZHENG Ke-yu, WEI Nian, YANG Feng-xia, ZHANG Duan-ming, QI Ya-jun
    Potassium tantalate niobate (KTa0.4Nb0.6O3, KTN) nanoparticles of perovskite structure were success-sfully synthesized by a solvothermal method. The KTN nanoparticles synthesized at 250 ! for 8 h with 1 to 4 M KOH concentration using isopropyl alcohol [(CH3)2 CHOH] as the solvent was composed of a single phase of cubic perovskite structure. Futhermore, the KTN powers synthesized at the same conditions besides of using (CH3)2CHOH/H2O as a solvent compose of a single phase of tetragonal perovskite structure. The nanoparticles exhibit a mixture of cubic and prism-like shapes with lengths of 100 nm to 500 nm and average cross sections of 200×200 nm2. The solvent dependence of the powder formation is discussed. X-ray diffraction and electron diffraction results show that the powders have the needed tetragonal perovskite structure. The band gap of KTN nanoparticles is determined to be 3.26 eV from the optical absorption spectra.
  • L? Xiao-jing, WU Ju, XU Bo, ZENG Yi-ping, WANG Biao-qiang, WANG Zhan-guo
    An AlAs layer of two or three monolayers was inserted beneath the strained InAs layer in the fabrication of InAs nanostructure on the In0.53Ga0.47As and In0.52Al0.48As buffer layer lattice-matched to InP(001) substrate using molecular beam epitaxy. The effects of AlAs insertion on the InAs nanostructures were investigated and discussed.
  • HUANG Liang, Kwangho PARK, LAI Ying-Cheng, WANG Xingang, LAI Choy Heng, Robert A. GATENBY
    Synchronization in complex networks has been an active area of research in recent years. While much effort has been devoted to networks with the small-world and scale-free topology, structurally they are often assumed to have a single, densely connected component. Recently it has also become apparent that many networks in social, biological, and technological systems are clustered, as characterized by a number (or a hierarchy) of sparsely linked clusters, each with dense and complex internal connections. Synchronization is fundamental to the dynamics and functions of complex clustered networks, but this problem has just begun to be addressed. This paper reviews some progress in this direction by focusing on the interplay between the clustered topology and network synchronizability. In particular, there are two parameters characterizing a clustered network: the intra-cluster and the inter-cluster link density. Our goal is to clarify the roles of these parameters in shaping network synchronizability. By using theoretical analysis and direct numerical simulations of oscillator networks, it is demonstrated that clustered networks with random inter-cluster links are more synchronizable, and synchronization can be optimized when inter-cluster and intra-cluster links match. The latter result has one counterintuitive implication: more links, if placed improperly, can actually lead to destruction of synchronization, even though such links tend to decrease the average network distance. It is hoped that this review will help attract attention to the fundamental problem of clustered structures/synchronization in network science.
  • ZHAO Ming, ZHOU Tao, CHEN Guan-rong, WANG Bing-hong
    The structural and dynamical properties, particularly the small-world effect and scale-free feature, of complex networks have attracted tremendous interest and attention in recent years. This article offers a brief review of one focal issue concerning the structural and dynamical behaviors of complex network synchronization. In the presentation, the notions of synchronization of dynamical systems on networks, stability of dynamical networks, and relationships between network structure and synchronizability, will be first introduced. Then, various technical methods for enhancing the network synchronizability will be discussed, which are roughly divided into two classes: Structural Modification and Coupling-Pattern Regulation, where the former includes three typical methods—dividing hub nodes, shortening average distances, and deleting overload edges, while the latter mainly is a method of strengthening the hub-nodes’ influence on the network.
  • PANG Xiao-feng
    A new theory of bio-energy transport along protein molecules, where energy is released by the hydrolysis of adenosine triphosphate (ATP), has recently been proposed for some physical and biological reasons. In this theory, Davydov’s Hamiltonian and wave function of the systems are simultaneously improved and extended. A new interaction has been added into the original Hamiltonian. The original wave function of the excitation state of single particles has been replaced by a new wave function of the two-quanta quasi-coherent state. In such a case, bio-energy is carried and transported by the new soliton along protein molecular chains. The soliton is formed through the self-trapping of two excitons interacting with amino acid residues. The exciton is generated by the vibration of amide-I (C=O stretching) arising from the energy of the hydrolysis of ATP. The properties of the soliton are extensively studied by analytical methods and its lifetime for a wide range of parameter values relevant to protein molecules is calculated using the nonlinear quantum perturbation theory. The lifetime of the new soliton at the biological temperature of 300 K is large enough and belongs to the order of 10-10 s or τ/τ0 ≥ 700. The different properties of the new soliton are further studied. The results show that the new soliton in the new model is a better carrier of bio-energy transport and it can play an important role in biological processes. This model is a candidate of the bio-energy transport mechanism in protein molecules.