1997年, 第28卷, 第4期　
刊出日期：1997-12-15

  

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  Squeezing Properties of the Ion Traps

  FENG Mang, WU Juhao, WANG Kelin

  理论物理通讯. 1997, 28(4): 385-390.

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  With time and space transformation, we first solve the Schrodinger equation of the time-dependent harmonic oscillator (TDHO) system. The properties of the squeezing in the case of ω(t) =√U + VcosΩt, i.e., the Paul trap and ω(t) = ω₀ + ω₁secλt, namely a stable frequency interfered by a single-pulsing-type disturbance, are investigated by using function series expansion. Results in the former case are compared with the numerical calculations carried out before. It is found that the condition related to the most strong squeezing is the direct result of our method, not any approximation is needed. Solutions of the latter one are valuable for the study of the ion trap, where different cases are studied in detail. Finally we made a discussion for the measurement and observation of a trapped ion by using squeezing properties.
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  Supercurrent and Its Quantum Statistical Properkies in Mesoscopic Josephson Junction in the Presence of Nonclassical Light Fields

  KUANG Leman, WANG Yiwen, GE Molin

  理论物理通讯. 1997, 28(4): 391-400.

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  In this paper, we study the supercurrent in a mesoscopic Josephson junction (MJJ) and its quantum statistical properties in the presence of nonclassical light fields. We investigate in detail the influence of external nonclassical light fields on current-voltage step structures of the MJJ. We also study in detail quantum statistical properties of the supercurrent when the external quantum electromagnetic fields are even and odd coherent-sta!e light fields. It is shown that the supercurrent in the MJJ exhibits both squeezing effect and quantum coherence. It is demonstrated that the MJJ can feel the difference not only between classical light fields and nonclassical light fields but also between different nonclassical light fields.
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  Coherent Population Trapping in a Λ-Configuration Photoionization System in the Presence of an Autoionizing State

  LI Gaoxiang, PENG Jinsheng, ZHOU Peng

  理论物理通讯. 1997, 28(4): 401-406.

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  We investigate the atomic coherent population trapping in the system of two-mode quantized field interacting with a A-configuration atom with two lower bound states, one autoionizing state and a flat atomic continuum. The states of the field which traps the atom in its two lower bound states are given and the influence of the field induced continuum structure is examined.
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  Theoretical Investigation of the Int erlayer Exchange Coupling

  SHEN Rui, XIAO Mingwen, LI Zhengzhong

  理论物理通讯. 1997, 28(4): 407-414.

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  We obtain the exact Green's functions of the Anderson s-d mixing model for magnetic multilayers within the mean-field theory of the on-site Coulomb repulsion. It is shown that the coupling oscillates in the experimental range of the spacer thickness only when the s-d mixing is strong enough, and that the polarization energies of s and d electrons weaken the intedayer coupling remarkably. We also find that the thermal dependence is determined by both the properties of the Fermi surface of the spacer and the exchange splitting between the two spin subbands in the ferromagnetic layers.
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  Energy States in a Dimerized Chain with an Impurity

  ZHAO Xiangeng

  理论物理通讯. 1997, 28(4): 415-418.

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  The quantum coherent property of excitons (electrons) in a dimerized chain with the interaction of an impurity is studied analytically. The energy spectrum and the wavefunctions for both the extended states and the localized states are obtained explicitly, from which the effects of the impurity and the electron-phonon interaction (which models the dimerized chain) are manifested. The symmetry properties for the energy states in the parameter space and the real space are also given.
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  Failure of Linear-Response-Theory for NaK Alloys

  Y. M. GU, D. M. Bylander, Leonard Kleinman

  理论物理通讯. 1997, 28(4): 419-426.

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  As we previously did for Na, we calculate the Gibbs free energy of liquid and solid K using linear-response-theory and molecular dynamics to obtain its melting temperature. The agreement with experiment is even better than that obtained for Na. We then attempted to determine the formation enthalpy of liquid and solid NaK alloys without success and discuss possible reasons for the failure of the method to yield agreement with experiment.
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  Calculation of Spectral Dimension on Inhomogeneous Fractal Lattices

  GUO Wen'an, YANG Zhanru, QIN Yong

  理论物理通讯. 1997, 28(4): 427-432.

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  We propose a scheme to derive the spectral dimension of inhomogeneous fractal lattice via renormalization procedure, in which the distribution of masses on the sites of fractals is introduced. The spectral dimension of diamond-type hierarchical lattice and Sierpinski gasket with b = 3 are re-investigated in this way. Moreover, the variants of Sierpinski gaskettype fractals are studied, the results show that the spectral dimension is independent of the details of internal structure of fractal, and thus implies the existence of universality. The source of the universality is also analyzed.
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  Effects of the Three-Nucleon Forces from Different Meson Exchanges on the Triton Binding Energy

  Ahmed Osman, M. A. Allam

  理论物理通讯. 1997, 28(4): 433-440.

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  Effects of the three-nucleon forces on the triton binding energy are investigated using different models for which the xN scattering amplitudes for the off-mass-shell pions are extrapolated from the on-mass-shell data. In the independent model potential, the threenucleon forces are constructed using the chiral symmetry through partial conservation of the axial current vectors and current algebra. On the other hand, the three-nucleon forces in the dependent model potential are derived from an effective Lagrangian which is constrained by chiral and gauge symmetry. The effect of the long range 2π and the repulsive ap-exchange three-nucleon forces on the triton binding energy are investigated. The bound state triton binding energies are then calculated by solving the Faddeev equations with a Hamiltonian including the three-nucleon forces, using different nucleon-nucleon interactions. The pionic form factors are considered with different sets of the form factor cutoff,parameter Λ. The 2π-exchange forces with S- and P-wave amplitudes are found to overbind the triton binding energy by about 0.4～Y 1.6 MeV. However, xp-exchange forces are found to reduce the 2π exchange forces by about 18% of its contribution, to the triton binding energy.
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  The Non-Equilibrium Entropy in Nuclear Reaction System

  WU Shunguang, SUN Xiuquan, ZHANG Jingshang

  理论物理通讯. 1997, 28(4): 441-448.

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  The non-equilibrium entropies for both close and open systems are studied based on the nonlinear occupation number equation. The relations between transport coefficients and nuclear temperature parameter are obtained analytically. The single-particle occupation number equation for the open system is established and its numerical solutions are given. The entropies and occupation numbers with different emission rates are also calculated and compared with each other.
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  QCD Sum Rules and J/ψ Suppression in Hot Hadronic Matter and Quark-Gluon Plasma

  GAO Song, SU Rukeng, LI Xueqian

  理论物理通讯. 1997, 28(4): 449-454.

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  A consistent treatment based on the QCD sum rules at finite temperature has been established to calculate the J/ψ suppression in hot hadronic matter (HM) and quarkgluon plasma (QGP) respectively. We have found that the J/ψ suppression occurs in both hadronic matter and quark-gluon plasma, but a J/ψ mass shift of about 0.49 GeV exists in QGP background only. The results obtained by QCD sum rules and by potential model are compared.
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  Intrinsic Regularization Method in QCD

  CAI Yu, GUO Hanying, GAO Daoneng

  理论物理通讯. 1997, 28(4): 455-462.

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  There exist certain intrinsic relations between the ultraviolet divergent graphs and the convergent ones at the same loop order in renormalizable quantum field theories. Whereupon we may establish a new method, the intrinsic regularization method, to regularize those divergent graphs. In this paper, we apply this method of QCD at the one-loop order. It turns out to be satisfactory: The gauge invariance is preserved manifestly and the results are the same as those derived by means of other regularization methods.
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  Evaluation of Some Lattice SU(2) Group Integrals

  ZHENG Xite

  理论物理通讯. 1997, 28(4): 463-468.

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  A procedure for deriving a set of formulas of SU(2) group integrals in the lattice gauge theory by extensively using the properties of modified Bessel functions is presented. These formulas are extremely useful in the higher-order calculations of the cumulant expansion.
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  Spectral Functions for Composite Fields and Discontinuity in Two-to-Two Scattering Amplitude

  WANG Enke, ZHANG Xiaofei, LI Jiarong

  理论物理通讯. 1997, 28(4): 469-474.

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  A spectral representation for two-point Green function for arbitrary composite field operators is derived in Thermo,Field Dynamics (TFD). The application to two- to-two scattering at finite temperature shows that the corresponding cross section is of the form σ = σ_d - σ_i for two bosons or two fermions, which is similar to the decay rate Γ = Γ_d - Γ_i for single boson. The cross section ad for the scattering process and ui for the corresponding inverse process determine the rate of approaching to equilibrium of the particle distribution function.
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  Chaotic Behavior in the Rescattering Process of Optical Field Ionization

  LIU Jie, CHEN Shigang

  理论物理通讯. 1997, 28(4): 475-478.

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  In this paper we describe the rescattering process in optical field ionization through a new model which improves the well-known quasi-static model by adding Coulomb potential in its second procedure. We find that this new model shows chaotic scattering. Nonlinear theory is applied to analyze the system. We also find that there exist chaotic layers and selfsimilar fractal structure and those unstablemanifolds which constitute the chaotic scattering pattern.
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  Exact Solutions of the Matrix KP Equation

  WU Zuyu, ZHANG Dehai

  理论物理通讯. 1997, 28(4): 479-482.

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  The matrix KP equation is a many component extension of the ordinary KP (Kodomtsev-Petvjshvilli) equation. Although the matrix KP equation is very important, however,its explicit exact solutions have not been reported up to now. In this letter we give a method to construct the matrix KP hierarchy and its exact solutions. Then we give here the explicit expressions of the exact solutions of the matrix KP equation with arbitrary soliton number.
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  Differential Calculus on Quantum Lorentz Group

  WANG Shikun, WU Ke

  理论物理通讯. 1997, 28(4): 483-488.

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  In this paper, we discuss the bicovariant differential calculus on quantum Lorentz group, and provide corresponding de Rham complex and Maurer-Cartan formulae.
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  Laguerre Polynomial States and Phase States in k-Photon Sub-Fock Space

  FAN Hongyi, FAN Yue

  理论物理通讯. 1997, 28(4): 489-492.

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  Using k-photon Brandt-Greenberg operators we introduce the concept of field intensity-dependent squeezing, and construct the minimum uncertainty states for this squeezing,which turns out to be a Laguerre polynomial state in sub-Fock space. The k-photon phase states is also derived, which turns out to be an SU(1,1) generalized coherent state.
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  Chiral Bosonized Versions Hidden in Chiral Schwinger Models

  MIAO Yangang, CHEN Chuanhong

  理论物理通讯. 1997, 28(4): 493-496.

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  The left- and right-handed chiral Schwinger models are re-examined by a modified chiral bosonization. Contrary to the usual chiral bosonization, we impose the chiral constraint on the right-handed chiral Schwinger model and the antichiral constraint on the left-handed one. The resulting chiral boson and theories are gauge-invariant and equivalent to one (free) cbiral boson and one antichiral boson respectively.
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  R_b and R_c in an Extended Standard Model

  ZHAO Wanyun

  理论物理通讯. 1997, 28(4): 497-498.

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  By the study for the mixing of a charm quark c and a new quark m with the mixing angle θ in an extended standard model, we obtain the theoretical values of R_b and R_c which are fairly accordant with the experimental values of R_b^{ex and R_cex.}