理论物理通讯

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On the Quantum Dynamic Theory of the MIT Output Coupler for the Bose-Einstein Condensation

SUN Changpu, ZHAN He, MIA0 Yuanxiu, LI Jianming

理论物理通讯. 1998, 29(2): 161-166.

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A linear quantum dynamic theory for output coupler of Bose-Einstein condensed atoms in a trap is considered with the Bogoliu bov approximation in the thermodynamical limit based on the recent MIT experiment (Phys. Rev. Lett. 78 (1997) 582) for atomic laser. In evolution of total system, the solution of the many-body problem shows a factorization of dynamic process, i.e., the wave function initially prepared in a direct product of a vacuum state and a coherent state remains in a direct product of coherent states at any instance. Physically, this factorizable structure predicts that an ideal condensate in the trap will remain in such a condensate state after the radiation frequency interaction while the output-coupler pulse of atoms forms a macroscopic quantum state in a propagating mode, i.e., the atomic laser.

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Structure and Liquid-Vapor Interface of a Simple Metal

LI Fengyin, ZHAO Meishan

理论物理通讯. 1998, 29(2): 167-168.

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This paper presents the results of a theoretical study of the structure of the liquidvapor interface of gallium, based on density functional pseudopotential representation of the electron-ion and the ion-ion interactions, and self-consistent quantum Monte Carlo simulation. These predictions of the bulk pair correlation function and the longitudinal density distribution are in very good agreement with the results of recent experimental studies.

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Decoherence Induced by Discontinuous and Stochastic Unitary Evolution of Qubits in Quanturn Computers

KUANG Leman

理论物理通讯. 1998, 29(2): 169-172.

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A new kind of decoherence in quantum computer memory, called intrinsic decoherence, is investigated in some details, which is caused by discontinuous and stochastic unitary evolution of qubits in quantum computers on a sufficient short time scale. It is found that the intrinsic decoherence leads to quasi-periodic decaying oscillations of the state fidelity of qubits in the time evolution. Schemes to reduce the intrinsic decoherence are proposed.

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Universal R-matrix of the Super Yangian Double DY (gl(1|1))

CAI Jinfang, WANG Shikun,WU Ke, XIONG Chi

理论物理通讯. 1998, 29(2): 173-176.

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Based on Drinfeld realization of super Yangian double DY (gl(1|1)), its pairing relations and universal R-matrix are given. By taking evaluation representation of universal R-matrix, another realization L^±(u) of DY (gl(1|1)) is obtained. These two realizations of DY (gl(1|1)) are related by the supersymmetric extension of Ding-fienkel map.

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Infrared Optical Absorptions in Corrugated Lateral Surface Superlattices

SUN Hong, HUANG Jinmin, YU Kinwah

理论物理通讯. 1998, 29(2): 177-186.

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The optical properties are investigated numerically in infrared (IR) regions for GaAs/AIAs corrugated lateral surface superlattices (CLSSLs) with short lateral periods. The calculations are carried out for refractive indexes and optical absorption coefficients with and without inclusion of electron interactions in an attempt to study the effects of intersubbahd plasmons on the IR optical properties of CLSSLs. As lateral periods of CLSSLs increase from 10 nm to 30 nm, their IR optical properties change from the behavior dominated by single electron transitions between conduction subbands to those dominated by intersubband plasmon excitations. Strong and sharp peaks in the optical absorption coefficients, large variations of the refractive indexes and strong anisotropic optical properties of CLSSLs are predicted in IR regions.

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Fermion-Spin Approach to Study the Doping Dependence of Antiferromagnetism in the Copper Oxide Material

FENG Shiping, SONG Yun, HUANG Zhongbing, BAI Wenjun

理论物理通讯. 1998, 29(2): 187-194.

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Within the fermion-spin theory, we study the ground-state properties of the copper oxide materials by considering quantum fluctuations of spinons in the random-phaseapproximation (RPA). The RPA ground-state at half-filling is the magnetized π-flux state with the energy E₀=-0.332J per bond and the staggered magnetization M = 0.327. Away from half-fiing this staggered magnetization vanishes around doping δ= 5% for the reasonable parameter t/J = 5, which is in very good agreement with the experiments on copper oxide materials. Our results indicate that both hole dopings and quantum fluctuations of spinons lead to a strong suppression of the antiferromagnetic long-range order.

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Thermal-Noise Temperature in GaAs-AlGaAs Heterojunctions

DONG Bing, LEI Xiaolin

理论物理通讯. 1998, 29(2): 195-200.

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The theory of hot-electron thermal noise in quasi-two-dimensional systems under a strong dc electric field proposed by LEI et a1.^[4] is extended to the case of multi-subband occupations. As an example, we use this extended method to calculate the thermal-noise temperature of GaAs-AlGaAs heterojunction systems at different dc electric fields including the contributions of the lowest and next lowest subbands. We find that, in comparison with the results of the one-subband theory, the inclusion of a higher subband yields an electron densitydependent decrease of the electron temperature and the thermal-noise temperature and a reduction of the cooling effect. The numerical results also confirm the fact that considering only the lowest subband of heterojunction systems is a sufficiently good approximation in the case of sufficiently low electron densities not only for common transport problems but also for thermal noise.

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Critical Properties of Anisotropic Heisenberg Ferromagnet with Spin-One

JIANG Qing, CAO Haixia, LI Zhenya

理论物理通讯. 1998, 29(2): 201-206.

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Combining the two-site cluster approximation with the discretized path-integral representation (DPIR) and Suzuki-Trotter formalism, the critical properties of anisotropic Heisenberg ferromagnet with a crystal field are studied. We find that the tricritical point can appear in the case of negative crystal field. And the exchange anisotropy not only reduces the critical temperature and tricritical point, but also makes re-entrant phenomena instead of the existence of the tricritical point when the exchange anisotropic parameter is larger than a critical value.

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Lattice Dynamics Study of Microstructures of Electrorheological Fluids

WANG Zuowei, LIN Zhifang, TAO Ruibao

理论物理通讯. 1998, 29(2): 207-212.

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The lattice dynamics method is used to study the stability of the chain structures formed in electrorheological (ER) fluids. The appearance of the soft modes in the phonon dispersion of the structures indicates that the chains tend to distort and aggregate into thicker columns due to the electrostatic attractive forces and thermal generated forces between them. The results show that the stability of the chains relies on their width and the separation between them. The complete chain structures are more stable than the chains with defects. The results can be used to elucidate the densification phenomenon of the chains in the structuring process of ER fluids in the quiescent state.

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Fokker-Planck Equation of a Stochastic System Driven by Spatially-Related Noises

LI Jinghui, HUANG Zuqia

理论物理通讯. 1998, 29(2): 213-216.

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In this paper we study a general stochastic system driven by the spatially-related Gaussian white noises. The corresponding Fokker-Planck equation is calculated; and some typical cases are analyzed. Finally, by the Fokker-Planck equation derived in the paper we study a single bistable kinetic process with spatially-related noise. The results obtained in the paper provide a correct foundation for the.treatment of the stochastic systems driven by spatially-related noises.

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Three-Dimensional Vertex Model Related BCC Model in Statistical Mechanics

HU Zhanning

理论物理通讯. 1998, 29(2): 217-224.

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In this paper, a three-dimensional vertex model is obtained. It is a duality of the three-dimensional integrable lattice model with N states proposed by Boos, Mangazeev, Sergeev and Stroganov. The Boltzmann weight of the model is dependent on four spin variables, which are the linear combinations of the spins on the corner sites of the cube, and obeys the modified vertex-type tetrahedron equation. This vertex model can be regarded as a deformation of the one related to the three-dimensional Baxter-Bazhanov model. The constrained conditions of the spectrums are discussed in detail and the symmetry properties of weight functions of the vertex model are presented.

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Topological Analysis of the EBL Model for the Chaotic NMR Laser

WU Zuobing, LIU Junxian

理论物理通讯. 1998, 29(2): 225-230.

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By determining relative rotation rates of the extended Bloch-type model, a consistent topological description for the model and the chaotic NMR laser at the parameter regime investigated is indicated. A geometrical method for calculating relative rotation rates, which is different from that of constructing the template, is proposed by establishing a symbolic plane in terms of the ordering of forward. and backward sequences encoding unstable periodic orbits.

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On the q-Deformation of Heisenberg Algebra

HOU Boyuan, XU Lianchao, ZHOU Shanyou

理论物理通讯. 1998, 29(2): 231-236.

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This paper deals with a class of q-deformations of Heisenberg algebra which contains the q-Heisenberg algebra, the q-oscillator algebra and others. Their representation theory is considered for q being generic or a root of 1. Finally, the structure of Hopf algebra in a quotient algebra is also discussed.

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General Decomposition of Spin Connection and Topological Structure in Gauss-Bonnet-Chern Density

DUAN Yishi, LI Xiguo

理论物理通讯. 1998, 29(2): 237-244.

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By means of devices of geometric algebra the general decomposition of spin connection on the sphere bundle of a compact n-dimensional Riemannian manifold has been studied in detail. Using this decomposition theory it is shown that the Gauss-Bonnet-Cherniensity of the Euler-PoincarB characterictic can be expressed in terms of a smooth vector field φ and take the form of the 6 function δ(φ). The topological structure in Gauss-Bonnet-Chern theorem is reviewed.

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Exceptional Quasilinear Hyperbolic Systems of Conservation Laws

KONG Dexing, NI Guangjiong

理论物理通讯. 1998, 29(2): 245-248.

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In this note we take into consideration of Temple's systems, a class of quasilinear hyperbolic systems of conservation laws which enjoy a remarkable property that the shock and rarefaction curves coincide. We give a criterion of how to verify a system to be of Temple's type, state and construct some new examples of such systems and show that this kind of exceptional systems has infinite convex entropies.

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Description of the Structure of ^88-96Sr in the IBM

LONG Guilu, ZHANG Jinyu, TIAN Lin

理论物理通讯. 1998, 29(2): 249-256.

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The neutron-rich even-even Sr isotopes are studied in the interacting boson model. The semi-closed nucleus ⁸⁸Sr is studied in the framework of the IBMI, and ^90-96Sr are studied in the neutron-proton interacting boson model. The spectrum and E2, M1 transition properties are calculated and compared with experiment.

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Study of Pion-Source Size in Relativistic Nuclear Collisions

ZHENG Yuming, Osamu Miyamura, Kenji Kumagai

理论物理通讯. 1998, 29(2): 257-264.

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The BoseEinstein correlation of pion pairs is calculated using the space-time and four-momentum distributions Gom an event generator URASiMA for 200 AGeV/c Pb + Pb and compared to pion correlation measurement from CERN experiment of NA44. The spacetime distributions of the simulated pion-emitting source are also analyzed.

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Pion Inelastic Scattering from l18Sn with ExcitaXion to 3₁^- State

LIU Yuxin, ZHANG Yushun, ZHAO Enguang, SUN Hongzhou

理论物理通讯. 1998, 29(2): 265-270.

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The description of the medium energy pion-nucleus inelastic scattering which excites the target from ground state to a negative parity state is discussed in the approach of combining Eikonal approximation with. spdf Interacting Boson Model. The calculated differential cross sections of the 163 MeV π^±-l18 sn scattering with excitation from 0₁⁺. state to 3₁^-; state and the deformation parameter of the 3₁^-; state agree with experimental data quite well. It indicates that the low-lying states of ¹¹⁸Sn can be described in the IBM. The effects of multiple scattering and nuclear structure correlation are shown to be important in the scattering process.

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Study on υ_μ, υ_γ, Decays and CP Non-Invariance at Early Epoch of the Universe

DAI Wusheng, GAO Song, LI Xueqian

理论物理通讯. 1998, 29(2): 271-276.

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We study the υ_μ and υ_γ decays in the early epoch of the universe. If m_{υ_γ} > 2m_e, there would be a CP asymmetry between υ_γ→e⁺+e^-+υ_e and υ_γ→e⁺+ e^-+ υ_e. The resultant CP non-invariance is a function of temperature and density and can reach l0^-7 for a reasonable temperature range, but it is noticed that if m_{υ_γ} > 2υ_μ～200 MeV, the CP non-invariance can be much larger.

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A New Prediction for Large Rapidity Gap Events in e⁺ e^- Annihilation

WANG Qun, XIE Qubing

理论物理通讯. 1998, 29(2): 277-280.

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A new approach is proposed to predict large rapidity gap events in e⁺ e^- annihilation. It is based on the mechanism of soft color interaction, which is successful in describing large rapidity gap events in ep collision. It is shown that the ratio of large rapidity gap signal to the background brought by fluctuations is greatly enhanced at appropriate conditions. So the mechanism of soft color interaction can be tested in e⁺ e^- annihilation.

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Vacuum Polarization Bubble Effects on the Triangle Relations for B Meson Charmless Decay Amplitudes

LIU Jiafu, CHAO Kuangta

理论物理通讯. 1998, 29(2): 281-286.

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Assuming that factorization is valid and that contributions of the exchange, annihilation, and penguin-annihilation diagrams are negligible, we study the effects of the QCD vacuum polarization bubbles on the decay amplitudes of some B meson charmless decays into two light pseudoscalars. The bubbles have much less effects on B⁰→π⁺π^-, π^-K⁺, π⁰K⁰ than on B⁰→π⁰π⁰ thus the triangle relation √2A(B⁺→π⁺π⁰) = A(B⁰→π^-K⁺)/R_u+√2A(B⁰→π⁰K⁰)/R_u is changed slightly while √2A(B⁺→π⁺π⁰)=√2A(B⁰→π⁰π⁰)+A(B⁰→π⁺π^-) is altered significantly. This may indicate that in order to test or use these triangle relations other higher order QCD corrections should also be carefully taken into consideration.

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High Energy P+P(P)→P+P(P)+X_j(cc) Process and Two Methods for Calculating Double-Pomeron Exchange Mechanism

PENG Hong'an, XU Jiasheng

理论物理通讯. 1998, 29(2): 287-294.

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Using the X_j(cc) double diffractive production processes in high energy P + P(P) collisions, we have comparatively discussed the D-L phenomenological method of calculating the double-pomeron exchange (DPE) and the method based on the exchange of a pair of nonperturbative color singlet gluons. From the energy dependence of the total cross sections calculated with the two methods we find the two methods fitting well. We conclude that the two methods are consistent.

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Faddeev-Jackiw Quantization and Its Application to the Linear σ Model for Disoriented Chiral Condensates

XU Xiaoming

理论物理通讯. 1998, 29(2): 295-302.

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The equivalence between the Faddeev-Jackiw formalism and Dirac-Bergmann algorithm is proved. A two-dimensional constrained system and a charged vector field are quantized in the Faddeev-Jackiw formalism. This symplectic method is technically developed, without recourse to Hamiltonian or Lagrangian, to quantize systems whose equations of motion are known. Examples are given to show this role. For constructing quantum approaches to the disoriented chiral condensates, the linear σ model is quantized in the instant form, light-cone form and covariant form.

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A (p, q)-Deformation of Quantum Mechanics

GONG Renshan

理论物理通讯. 1998, 29(2): 303-308.

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On a one-dimensional lattice with a geometric sequence spacing, the Hermitian conjugation of a (p, q)-derivative operator is discussed by means of (p, q)-integration. Then a (p, q)-deformation of both the Heisenberg algebra for the canonical coordinates and the Heisen berg-Weyl algebra for the harmonic oscillator is presented. It is shown that although in the algebraic aspect the (p, q)-deformation discussed here is identical with 9-deformation given by Truong, the (p, q)-deformed SchrGdinger picture is in fact different from the q-deformed one.

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Soliton-Like Bipolaron in Two-Dimensional Deformable Electron-Phonon System

WANG Yi, WANG Kelin, WAN Shaolong

理论物理通讯. 1998, 29(2): 309-312.

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Based on Emin's idea of deformation potential in deformable continuum, a bipolaron Hamiltonian is generalized to two-dimensional deformable electron-phonon system with the assumption of localized deformation potential of δ function. The dynamic properties of bipolaron are studied in the framework of Davydov's soliton theory, and a nonlinear Schrodinger equation is derived using the principle of least action. By function-series method, an exact two-dimensional (2D) soliton solution is obtained. We find that the center-of-mass motion of bipolaron is shown in a solitary wave form, and its relative motion is a harmonic one.

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Painlevé Analysis of a (2+l)-Dimensional Burgers Equation

CHEN Lili, LOU Senyue

理论物理通讯. 1998, 29(2): 313-316.

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A (2+1)-dimensional multi-component Burgers equation is obtained from the syrnmetry constraint of the modified Kadomtsev-Petviashvili equation. The model is proved to be integrable under the meaning that it possesses the Painlev6 property.

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δ-Function Operator Formulas of Photon Creation and Annihilation Operators

FAN Hongyi, FAN Yue

理论物理通讯. 1998, 29(2): 317-320.

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Using the technique of integration within an ordered product of operators we derive some &function operator formulas of photon creation and annihilation operators. Applications of these new formulas in simplifying some Louisell's operator theorems and in discussing the eigenket of creation operator are presented.

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1998年, 第29卷, 第2期　
刊出日期：1998-03-15

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选择文件类型/文献管理软件名称

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1998年, 第29卷, 第2期 刊出日期：1998-03-15

1998年, 第29卷, 第2期　
刊出日期：1998-03-15