2013年, 第60卷, 第06期　
刊出日期：2013-12-15

  

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  No Spin-Localization Phase Transition in the Spin-Boson Model without Local Field

  刘涛, 冯芒, 黎雷, 杨万里, 汪克林

  理论物理通讯. 2013, 60(06): 637-641.

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  We explore the spin-boson model in a special case, i.e., with zero local field. In contrast to previous studies, we find no possibility for quantum phase transition (QPT) happening between the localized and delocalized phases, and the behavior of the model can be fully characterized by the even or odd parity as well as the parity breaking, instead of the QPT, owned by the ground state of the system. The parity breaking mentioned in our case is completely different from the spontaneously broken symmetry relevant to the conventionally defined QPT in previous studies. Our analytical treatment about the eigensolution of the ground state of the model presents for the first time a rigorous proof of no-degeneracy for the ground state of the model, which is independent of the bath type, the degrees of freedom of the bath and the calculation precision. We argue that the QPT mentioned previously appears due to incorrect employment of the ground state of the model and/or unreasonable treatment of the infrared divergence existing in the spectral functions for Ohmic and sub-Ohmic dissipations.
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  Analytic Results in the Position-Dependent Mass Schrödinger Problem

  M.S. Cunha, H.R. Christiansen

  理论物理通讯. 2013, 60(06): 642-650.

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  We investigate the Schrödinger equation for a particle with a nonuniform solitonic mass density. First, we discuss in extent the (nontrivial) position-dependent mass V(x)=0 case whose solutions are hypergeometric functions in tanh²x. Then, we consider an external hyperbolic-tangent potential. We show that the effective quantum mechanical problem is given by a Heun class equation and find analytically an eigenbasis for the space of solutions. We also compute the eigenstates for a potential of the form V(x)=V₀ sinh²x.
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  A New Scheme for Probabilistic Teleportation and Its Potential Applications

  魏家华, 戴宏毅, 张明

  理论物理通讯. 2013, 60(06): 651-657.

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  We propose a novel scheme to probabilistically teleport an unknown two-level quantum state when the information of the partially entangled state is only available for the sender. This is in contrast with the fact that the receiver must know the non-maximally entangled state in previous typical schemes for the teleportation. Additionally, we illustrate two potential applications of the novel scheme for probabilistic teleportation from a sender to a receiver with the help of an assistant, who plays distinct roles under different communication conditions, and our results show that the novel proposal could enlarge the applied range of probabilistic teleportation.
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  Effect of Varying Dzyaloshinskii-Moriya Interaction on the Bistable Nano-Scale Soliton Switching

  L. Kavitha, M. Saravanan, V. Senthilkumar, D. Gopi

  理论物理通讯. 2013, 60(06): 658-662.

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  The effect of Dzyaloshinskii-Moriya (D-M) interaction on the bistable nano-scale soliton switching offers the possiblity of developing a new innovative approach for data storage technology. The dynamics of Heisenberg ferromagnetic spin system is expressed in terms of generalized inhomogeneous higher order nonlinear Schrödinger (NLS) equation. The bistable soliton switching in the ferromagnetic medium is established by solving the associated coupled evolution equations for amplitude and velocity of the soliton using the fourth order Runge-Kutta method numerically.
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  Lower Bound of Concurrence Based on Generalized Positive Maps

  秦慧慧, 费少明

  理论物理通讯. 2013, 60(06): 663-666.

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  We study the concurrence of arbitrary dimensional bipartite quantum systems. By using a positive but not completely positive map, we present an analytical lower bound of concurrence. Detailed examples are used to show that our bound can detect entanglement better and can improve the well known existing lower bounds.
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  Quantum Discord in any Mixture of Two Bi-Qubit Arbitrary Product States

  王胜房, 刘益民, 李国锋, 刘先松, 张战军

  理论物理通讯. 2013, 60(06): 667-672.

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  Quantum discord in any mixture of two bi-qubit arbitrary product states is studied with two different approaches. In the first approach the maximal classical correlations are obtained via numerical computations, while in the second approach they are analytically derived. Quantum correlations captured with both approaches completely coincide, as is in accord with the conclusion of Cen et al. [Phys. Rev. A 83 (2011) 054101]. The symmetry reduction of the concerned states concerning quantum correlations is accomplished. The captured discords are amply analyzed so that some inherent distinct properties are revealed.
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  Collective Excitations of Low Dimensional Trapped Bose-Condensed Gas

  罗运文, 陈继胜

  理论物理通讯. 2013, 60(06): 673-676.

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  In this paper, we investigate excited characteristic of the weakly interacting quasi-one-dimensional (1D) and quasi-two-dimensional (2D) Bose-Einstein condensation (BEC) in harmonic potential trap. The energy spectrum and the analytical expression of the sound velocity are obtained and analyzed. Compared with 3-Dimensional homogeneous Bose-condensed gas occasion, the sound velocity of 2D Bose-Einstein condensation in harmonic potential trap is smaller.
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  Why Matter Occupies so Large a Volume?

  E.B. Manoukian

  理论物理通讯. 2013, 60(06): 677-686.

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  The paper represents a rigorous treatment of the underlying quantum theory, not just in words but providing the underlying technical details, as to why matter occupies so large a volume and its intimate connection with the Pauli exclusion principle, as more and more matter is put together, as well as of the contraction or shrinkage of "bosonic matter", upon collapse, for which the Pauli exclusion is abolished. From the derived explicit bounds of integrals of powers of the particle number densities, explicit bounds on probabilities of the occurrences of the events just described are extracted. These probabilities lead one to infer the change of the "size" or extension of such matter, upon expansion or contraction, respectively, as their content is increased.
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  Interpretation of Rotation Curves of Spiral Galaxies in Modified Teleparallel Gravity

  K. Nozari, R. Shojaee, S. Karimzadeh

  理论物理通讯. 2013, 60(06): 687-690.

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  There is a significant difference between the calculation based on the theory of general relativity and observation of rotation curves of spiral galaxies. To describe this discrepancy, two distinct theories have been proposed so far: existence of dark matter and modification of underlying gravitational theory. In the absence of dark matter, it is assumed that the theory of general relativity on galactic scales needs to be modified. This letter is devoted to explaining this difference in a modified teleparallel gravity. We show that modified teleparallel gravity favors flatness of rotation curves of spiral galaxies much in the same way as observation shows.
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  De Broglie-Bohm Interpretation of Canonical Quantum Cosmology Implies Early Stages of the Universe Dominated by Radiation

  Ch'ng Han Siong, Shahidan Radiman

  理论物理通讯. 2013, 60(06): 691-694.

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  The Einstein's general relativity is formulated in the Hamiltonian form for a spatially flat, isotropic and homogeneous universe. Subsequently, we perform the canonical quantization procedure to the Hamiltonian to obtain the Wheeler-DeWitt equation. Solving the Wheeler-DeWitt equation and employing the de Broglie-Bohm interpretation to the wave function of the universe, we obtain a new version of spatially flat Friedmann equation for the early universe where the scale factor of the universe is taken to be sufficiently small.
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  Statistical Entropy of an Acoustic Black Hole in Bose-Einstein Condensates

  马孟森, 赵惠华, 赵仁

  理论物理通讯. 2013, 60(06): 695-698.

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  The entanglement entropy of an acoustic black hole in a Bose-Einstein condensates (BEC) is derived, which is associated with the phonons generated via the Hawking mechanism in a sonic hole. Considering the dispersion relation of a BEC, we recalculate the entanglement entropy of the acoustic black hole by means of statistical method in two limits. We find that the entropy is still proportional to the area of event horizon, but with a coefficient dependent on the infrared cutoff.
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  Double Reduction and Exact Solutions of Zakharov-Kuznetsov Modified Equal width Equation with Power Law Nonlinearity via Conservation Laws

  韩众, 张玉峰, 赵忠龙

  理论物理通讯. 2013, 60(06): 699-706.

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  The conservation laws for the (1+2)-dimensional Zakharov-Kuznetsov modified equal width (ZK-MEW) equation with power law nonlinearity are constructed by using Noether's approach through an interesting method of increasing the order of this equation. With the aid of an obtained conservation law, the generalized double reduction theorem is applied to this equation. It can be shown that the reduced equation is a second order nonlinear ODE. Finally, some exact solutions for a particular case of this equation are obtained after solving the reduced equation.
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  A Lattice Hydrodynamic Model for Traffic Flow Accounting for Driver Anticipation Effect of the Next-Nearest-Neighbor Site

  彭光含, 聂方彦, 汪胜辉

  理论物理通讯. 2013, 60(06): 707-713.

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  In this paper, a new lattice hydrodynamic model is proposed by incorporating the driver anticipation effect of next-nearest-neighbor site. The linear stability analysis and nonlinear analysis show that the driver anticipation effect of next-nearest-neighbor site can enlarge the stable area of traffic flow. The space can be divided into three regions: stable, metastable, and unstable. Numerical simulation further illuminates that the driver anticipation effect of the next-nearest-neighbor site can stabilize traffic flow in our modified lattice model, which is consistent with the analytical results.
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  Scalars and Neutral Fermions on the Background with Hyperscaling Violation

  白楠, 方超, 高怡泓, 奇官布, 徐孝宝

  理论物理通讯. 2013, 60(06): 714-720.

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  We study the scalar and fermionic retarded Green's function on the background with hyperscaling violation by means of the prescriptions proposed in [J. High Eergy Phys. 09 (2002) 042; Fortsch. Phys. 57 (2009) 367]. For scalar field, we consider both massless and massive cases, and for spinor field, we further calculate the finite temperature correlator with the black hole background.
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  B⁰-B⁰ Mixing in Local Gauged Baryon and Lepton Numbers

  孙飞, 冯太傅, 罗国慧, 赵树民, 孙科盛, 寇丽娜

  理论物理通讯. 2013, 60(06): 721-726.

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  Using the effective Hamiltonian method, we analyze the B⁰-B⁰ mixing in the extension of the standard model (SM) where baryon number and lepton number are local gauge symmetries. The numerical results indicate the correction from the extra particles to the mass difference Δm_B is significant. There is a 60% enhancement compared to the SM prediction for Δm_B at most, which agrees with the current experimental result.
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  Production of Tetraquark State T_cc at B-Factories

  热依玛汗·热西丁

  理论物理通讯. 2013, 60(06): 727-730.

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  We study production of the tetraquark state T_cc via virtual photon at the B-factories in the QCD factorization framework. We predict the cross section of tetraquark state production in the leading order at the B-factories.
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  Control Protocol of Finite Dimensional Quantum Systems

  唐剑炬, 付洪忱

  理论物理通讯. 2013, 60(06): 731-737.

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  An analytic control protocol of two types of finite dimensional quantum systems is proposed. The system can be driven to an arbitrary target state using cosine classical fields in finite cycles. The control parameters which are time periods of interaction between systems and control fields in each cycle are connected with the probability amplitudes of target states via trigonometrical functions and can be determined analytically.
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  Localized States of an Excess Electron in an Ionic Cluster

  K.V. Grigorishin, B.I. Lev

  理论物理通讯. 2013, 60(06): 738-746.

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  A theory of an electron affinity for an ionic cluster is proposed both in a quasiclassical approach and with quantization of a polarization electric field in a nanoparticle. A critical size of the cluster regarding in formation of an electron's autolocalized state, dependencies of energy and radius of a polaron on a cluster's size are obtained by a variational method. It has been found that binding energy of the electron in the cluster depends on a cluster's radius but a radius of electron's auto-localization does not depend on the cluster's radius and it equals to the polaron radius in a corresponding infinity crystal. A bound state of the electron in a cluster is possible only if the cluster's radius is more than the polaron radius.
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  Positronium Decay in a Circular Polarized Laser Field

  陈裕启, 吴培

  理论物理通讯. 2013, 60(06): 747-752.

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  We calculate the lifetime of both the o-Ps and the p-Ps positronium annihilation decay Ps→γγ in the strong circular polarized laser field. We take a strategy of the factorization to separate the effects caused by the Coulomb interaction and the strong laser field interaction. It is factorized in the time direction but not in the space direction. Our results show that in the laser with long wavelength and high intensity, the lifetimes of those Ps states are dramatically increased. For CO₂ laser with 10 μm wavelength and 10¹³ W/cm² intensity, lifetime of the spin-single positronium is increased by 10⁸ times. Our result is consistent with those obtained by solving the Schödinger equation. This effect may be useful for the high harmonic generation (HHG) effects provided with the Ps [Phys. Rev. Lett. 70 (1993) 774; Phys. Rev. Lett. 93 (2004) 013601].
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  A New Cooperation Mechanism of Kinesin Motors when Extracting Membrane Tube

  汪自庆, 舒咬根, 黎明

  理论物理通讯. 2013, 60(06): 753-760.

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  Membrane tubes are important functional elements for living cells. Experiments have found that membrane tubes can be extracted from giant lipid vesicles by groups of kinesin. How these motors cooperate in extracting the membrane tube is a very important issue but still unclear so far. In this paper, we propose a cooperation mechanism called two-track-dumbbell model, in which kinesin is regarded as a dumbbell with an end (tail domain) tethered on the fluid-like membrane and the other end (head domain) stepping on the microtubule. Taking account of the elasticity of kinesin molecule and the excluded volume effect of both the head domain and the tail domain of kinesin, which are not considered in previous models, we simulate the growth process of the membrane tube pulled by kinesin motors. Our results indicate that in the case of strong or moderate exclusion of motor tails, the average number of motors pulling the tube can be as high as 9 and thus motors moving along a single microtubule protofilament can generate enough force to extract membrane tubes from vesicles. This result is different from previous studies and may be tested by future experiments.