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Volume 15 Issue 6
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Original Articles
A Hermitian Opetator Conjugate to Two-Mode Number-Difference Operator
FAN Hong-yi, WANG Yi-hua
Chin. Phys. Lett. 1998, 15 (6): 391-392 .  
Abstract   PDF(pc) (92KB) ( 415 )
For the Shapiro-Wagner-Hradil phase detection description the canonical commutation relation between phase angle ψ and two-mode number-difference operator D = aa - bb is constructed. Departing from [ψ, D] = -i, the phase angle Hermitian operator is derived in the newly obtained representation < ξ |, where | ξ > is the common eigenket of a + b and b + a.
Aharonov-Bohm-Type Electron Interference in a Two-Mode Squeezed Vacuum Field
SHAO Bin, ZOU Jian
Chin. Phys. Lett. 1998, 15 (6): 393-394 .  
Abstract   PDF(pc) (186KB) ( 359 )
Electron interference related to Aharonov-Bohm effect in the presence of the two-mode quantized radiation field is investigated. Characteristics of the temporal behavior of electron interference are discussed. It is shown that for the two-mode squeezed vacuum field the time evolution of the intensity of electron interference can exhibit very interesting periodic spontaneous collapse and revival (CR). In addition, the relation between CR and the quantum fluctuation in electron interference is also discussed.
Construction of General Unitary Transformation for Conditional Quantum Dynamics and Realization of Quantum Controlled Gates
WANG Xiao-guang, YU Rong-jin, FU Jian-zheng
Chin. Phys. Lett. 1998, 15 (6): 395-397 .  
Abstract   PDF(pc) (189KB) ( 341 )
By factorizing a general one-bit transformation matrix for one-bit gates in quantum computer, a general unitary transformation is constructed, which can serve as (controlled)m gate for the conditional quantum dynamics. When the quantized single-mode electromagnetic field containing n or no photons acts as the controlled bit, the quantum controlled-NOT gates and square root of the controlled-NOT gates in cavity-quantum electrodynamics are realized.
Driving Signals Induced Synchronization
LIU Zong-hua, CHEN Shi-gang, ZHANG Guang-cai
Chin. Phys. Lett. 1998, 15 (6): 398-400 .  
Abstract   PDF(pc) (214KB) ( 340 )
The aim of the present work is to generalize the method introduced by Güémez et al. [Phys. Rev. E52 (1995) R2145] Using feedback scheme, two systems can be synchronized by signals or variables which come from the driving system. Furthermore, it is possible for the systems to be synchronized by different driving signals which come from the third or fourth system. So the unmasking procedure becomes more difficult. Numerical simulations are given.

Stochastic Estimations of Fermion Matrix Determinants with Unbiased Subtractions
YING He-ping
Chin. Phys. Lett. 1998, 15 (6): 401-403 .  
Abstract   PDF(pc) (221KB) ( 548 )
The Padé-Z2 stochastic estimator is used to calculate the fermion matrix determinants and the determinant ratios with an unbiased variational scheme. The results on an 83 x 12 lattice with Wilson action show that the determinant ratio with a relatively small number of Z2 noises (e.g., 400) can be estimated by using the unbiased subtractions.
Deformed-Skyrme-Hartree-Fock Calculation on C Isotope
SHEN Yao-song, , ZHU Xiao-feng, REN Zhong-zhou
Chin. Phys. Lett. 1998, 15 (6): 404-406 .  
Abstract   PDF(pc) (247KB) ( 392 )
The ground state properties of deformed nuclei of C isotope are investigated by the Skyrme-Hartree-Fock theory with new force parameters SKI4 of Reinhard and Flocard [Nucl. Phys. A 584 (1995) 467]. Calculations show that the deformed-Skyrme-Hartree-Fock theory with above force parameters provides a good description on the binding energy, the various radii and deformation parameters of C isotope. The figure of the evolution of deformation for whole C isotope chain is plotted. A detailed discussion on numerical results is provided in the paper.
Stark Effect of a Three-Level Atom in a Circularly Polarized Electromagnetic Wave
ZENG Gao-jian, ZHANG Jing-tao
Chin. Phys. Lett. 1998, 15 (6): 407-409 .  
Abstract   PDF(pc) (162KB) ( 440 )
The Schrödinger equation of a three-level atom in an electromagnetic wave of circular polarization is established. The solution to this equation shows that under the action of the circular polarized electromagnetic wave, the levels of a Σ-type atom split into nine sublevels, while those of a V-type or Λ-type atom split into six sublevels. By means of some special tuning ways and approximation conditions, the energies of the spilt levels are expressed in simpler forms.
Trapping of Atoms in Jaynes-Cummings Model
LI Yuan-jie, WANG Gang, WU Ying
Chin. Phys. Lett. 1998, 15 (6): 410-412 .  
Abstract   PDF(pc) (156KB) ( 383 )
In this paper, a semiclassical approach to trapping problem of atoms in Jaynes-Cummings model is presented. The detuning is expressed by considering detuning as superposition of plenty of harmonic waves. Appearance of trapping atoms is found. On basis of the model, quantum chaos movement of atoms irradiated with strong laser is discussed.
Preliminary Results on the First Optical Molasses of Cs Atoms in China
HOU Ji-dong, LI Yi-min, YANG Dong-hai, WANG Yi-qiu
Chin. Phys. Lett. 1998, 15 (6): 413-415 .  
Abstract   PDF(pc) (203KB) ( 413 )
Based on an improved optical system, which consists of six laser diodes with two injection locking stages and control set-ups of the intensity and frequency of the laser, we have achieved the first optical molasses in China. The time-of-flight (TOF) signal of the cloud of Cs atoms has been obtained, and an analytical-formula for measuring the temperature of the atomic cloud from its TOF signal is given. The lowest temperature of the cloud of Cs atoms is measured to be 10μK.
Above Threshold Ionization Spectra of He in a Circularly Polarized Laser Field
CHEN Bao-zhen
Chin. Phys. Lett. 1998, 15 (6): 416-417 .  
Abstract   PDF(pc) (162KB) ( 360 )
A new analytic model for the above threshold ionization spectrum of He in a circularly polarized laser field is proposed. The experimental spectrum obtained by Mohideen et al. can be quite well described by this model. The spectra predicted by our model agree with experiment better than those of Reiss when the spatiotemporal profile of the laser pulse is taken into account and better than those of the Keldysh-Faisal-Reiss theory when the profile is not taken into account. At the same time, we find that the experimental value of the peak laser intensity was overstated by a factor of about 5. This result supports the previous similar claim by Reiss.
Continuous-Wave Output of 5.5 W at 532 nm by Intracavity Frequency Doubling of an Nd:YVO4 Laser
HE Jing-liang, HOU Wei, ZHANG Heng-li, WU Ling-an, XU Zu-yan, YANG Guo-zhen, WANG Jian-ming, ZHAO Zong-yuan, WU Xing, LI Jian
Chin. Phys. Lett. 1998, 15 (6): 418-419 .  
Abstract   PDF(pc) (177KB) ( 537 )
A maximum of 5.5 W of cw TEM00 mode output at 532nm has been obtained by intracavity frequency doubling with a KTP crystal in an Nd: YVO4 laser doubly-pumped with 20 W diode pumping power. The optical-optical conversion efficiency is 27.5%. The influence of thermal lensing at high pumping power in the end-pumped Nd:YVO4 laser is discussed. The Nd:YVO4 laser has a good power stability of 1.6%.

Ultrafast Modulation Spectroscopy in Four-Level System
YU Zu-he, MI Xin, JIANG Qian, LI Xiao-feng, FU Pan-ming
Chin. Phys. Lett. 1998, 15 (6): 420-422 .  
Abstract   PDF(pc) (237KB) ( 339 )
Based on the interference between two two-photon processes, we reported a four-level ultrafast modulation spectroscopy in Na vapor, where 3S, 3P, 5S, and 4D formed a four-level system. We studied the temporal behavior of the four-wave mixing signal intensity and obtained signal modulation with period 25fs, corresponding to the splitting between 5s and 4D. This technique can achieve Doppler-free precision in the measurement of the energy level splitting between two excited states which are dipolar forbidden from the ground state.
Two-dimensional Perturbative Analysis of Slant Grating in Photorefractive Crystals in an External Electric Field
JIANG Yong-yuan, FENG Yu-wen, ZHOU Zhong-xiang, LI Yan, SUN Xiu-dong, XU Ke-bin
Chin. Phys. Lett. 1998, 15 (6): 423-425 .  
Abstract   PDF(pc) (217KB) ( 511 )
A slant grating was recorded with two laser beams incident on photorefractive crystal in an external dc electric field. Two-dimensional perturbative analytical solution for the first two-order space-charge field for steady-state photorefractive slant grating recording has been obtained. It is shown that the inclusion of the longitudinal component of the space-charge field during photorefractive two-wave coupling can predict reduction of the fundamental harmonic and enhancement or reduction of the second-order harmonic for various applied field strength and various grating slant angles. The dependence of the first two-order harmonics on the slant angle and on the applied field strength is examined.
Second-Harmonic Generation in Thue-Morse Optical Superlattice
LIU Xian-jie, WANG Zhen-lin, WU Jun, MIN Nai-ben
Chin. Phys. Lett. 1998, 15 (6): 426-428 .  
Abstract   PDF(pc) (233KB) ( 453 )
A Thue-Morse optical superlattice made from a single crystal with laminar ferroelectric domain structure was proposed to realize second-harmonic generation. Due to the singular continuous Fourier spectrum in Thue-Morse sequence, this structure shows more plentiful harmonic spectrum, and the intense peaks can be classified according to their different intensity distributions within the superlattice. The harmonic spectra in real space and reciprocal space are presented and discussed.
Responses of a New Active Vibration Isolation System to Random Vibrations
ZHOU Ze-bing, LUO Jun
Chin. Phys. Lett. 1998, 15 (6): 429-431 .  
Abstract   PDF(pc) (256KB) ( 341 )
The responses of the test mass of the new active vibration isolation system incorporating a quasi-fixed reference system to two typical random vibrations such as Gaussian white noise and seismic noise in gravitational experiments are presented. A conclusion is obtained that the isolation performance of the new active vibration isolation system from random vibrations is better than that of the traditional one.
Observation of Drift Wave Propagation as a Source of Tokamak Edge Turbulence
WANG Gui-ding, LIU Wan-dong, YU Chang-xuan, WEN Yi-zhi, WANG Chao, PAN Ge-sheng, ZHUANG Ge, ZHAI Kan, XU Yu-hong, WANG Cheng, WAN Shu-de
Chin. Phys. Lett. 1998, 15 (6): 432-434 .  
Abstract   PDF(pc) (252KB) ( 439 )
Core and edge turbulences were measured by Langmuir probe arrays in the KT-5C tokamak plasma. The radial wavenumber spectra show a quasimode like structure which results in a net radial outward propagation of the turbulent fluctuations. The measured fluctuation levels and wave action fluxes are in good agreement with model predictions by Mattor et al., suggesting that drift wave propagation could be a source of edge turbulence.
Lower Hybrid Current Drive Effects on HT-7 Superconducting Tokamak
KUANG Guang-li, XU Wei-hua, ZHANG Xiang-qin, SHAN Jia-fang, LIU Yue-xiu, LIU Deng-cheng, ZHENG Guang-hua, LIU Fu-kun, LIN Jian-an, WU Jun-shuan, JIN Qian-chun, DING Bo-jiang, YANG Chun-sheng, ZHOU Yuan-wei, SHANG Lian-quan, XU Han-dong, FAN Heng-yu, FANG Yu-de, XIE Ji-kang, WAN Yuan-xi
Chin. Phys. Lett. 1998, 15 (6): 435-437 .  
Abstract   PDF(pc) (246KB) ( 461 )
Lower hybrid current drive (LHCD) experiments have been done on the superconducting Tokamak HT-7 by using a new developed long pulse megawatt lower hybrid wave system. An LHCD efficiency of 0.5 x 1019A.m-2/W in a pulse length of several hundreds of milliseconds has been achieved. After boronization of the tokamak vacuum vessel, considerable improvements of plasma energy confinement and particle confinement during LHCD phase have been achieved by adjusting wave spectra. An energy transfer from the lower hybrid wave to plasma bulk electrons has been demonstrated experimentally. A computer simulation of the LHCD experiments by using a ray tracing code combined with a two dimensional Fokker-Planck code is in good accordance with experimental measurements and suggests an important role of plasma current profile.
Raman Studies on Structure Transitions of Layered Ferroelectrics Ba2+xBi4-xTi5-xNbxO18
HAN Jie, ZOU Guang-tian, CUI Qi-liang, YANG Hai-bin, CUI Tian
Chin. Phys. Lett. 1998, 15 (6): 438-440 .  
Abstract   PDF(pc) (224KB) ( 491 )
Raman spectra of layered ferroelectrics Ba2+xBi4-xTi5-xNbxO18 (0 ≤ x ≤ 2) at room temperature in the range 20-1000cm-1 were investigated. Vibration modes were assigned with the use of internal mode approach. Two doping-induced structure phase transitions were observed at about x = 0.50 and x = 1.25, respectively. Raman spectra variations were analyzed according to the selection rules of BO6 octahedra in various symmetry. Polycrystalline samples were synthesized by solid state reaction method.

Lifetime Prediction and Reliability Evaluation of Si3N4 Ceramic
ZONG Xiang-fu, WANG Xu, WENG Yu-min
Chin. Phys. Lett. 1998, 15 (6): 441-443 .  
Abstract   PDF(pc) (185KB) ( 342 )
In this study, non-equilibrium statistical physics is used to estimate the time-dependent fracture of inhomogeneous Si3N4 ceramic. The effects of structural inhomogeneity on mechanical properties of the Si3N4 ceramic are discussed. The numerical calculations show that the average lifetime will increase by means of introducing suitable inhomogeneity in materials, but it is not monotonous.
Molecular Dynamics Simulation of MgSiO3 Perovskite
ZHOU Lin-xiang, J. R. Hardy, XU Xin
Chin. Phys. Lett. 1998, 15 (6): 444-446 .  
Abstract   PDF(pc) (222KB) ( 371 )
Using molecular dynamics to simulate MgSiO3 perovskite is performed to investigate its phase transitions and superionicity. These simulations has used parameter-free Gordon-Kim potentials and a novel technique to monitor the motion of ions which clearly demonstrates the sublattice melting of ions O2- and the rotations of SiO6 octahedra. MgSiO3 has to undergo a few of phase transitions, then enter into the cubic phase. In particular, there is a transitional phase between orthorhombic phase and cubic phase. There are a superionc phase and the cubic phase in magnesium-rich silicate perovskite. This superionic phase occurs after the onset of cubic phase before the melting point. The onset temperature Tc for superionicity is about 200-700K below the melting point Tm, Tc/Tm ~0.92.
Photoconductivity Decay Under Illumination of a Pulsed Laser with Unfocused or Focused Beam
WU Zong-sen, SUN Xiao-tian, ZHENG You-dou, CHEN Zhi-zhong, SHEN Bo
Chin. Phys. Lett. 1998, 15 (6): 447-449 .  
Abstract   PDF(pc) (188KB) ( 476 )
Photoconductivity decay (PCD) in semiconductors is investigated by a pulsed laser with an unfocused or a focused beam. The rigorous solutions of PCD under illumination with two different types of laser beams, unfocused and focused, are derived separately. The experimental results of PCD are compared with the theory using Ge-based GaN under illumination of a pulsed Nd:YAG laser at 355nm. The experimental and numerical results are in good agreement.
Effects of Flux Creep on the Magnetization Curves of High-Temperature Superconductors
WEI Chong-de
Chin. Phys. Lett. 1998, 15 (6): 450-452 .  
Abstract   PDF(pc) (195KB) ( 447 )
The effects of flux creep on the magnetization curves of high-temperature superconductors are investigated numerically for Anderson-Kim model. The pinning energy at zero current density, Uc, greatly influences the flux penetration process, a larger Uc, value reults in a larger penetration field. The characteristic of the magnetization curve is also a function of Uc. The magnetization M and ΔM increase with the increasing Uc and depend on the magnetic induction B, so the critical current formula based on Bean model is pot accurate, especially for high-Tc superconductor, for which flux creep is a large effect.
An Analytical Expression of Magic Angle Spinning Nuclear Magnetic Resonance Free Induction Decay in Two-Site Exchange Problem
SHEN Yi-min, KAJI Hironori, HORII Fumitaka
Chin. Phys. Lett. 1998, 15 (6): 453-454 .  
Abstract   PDF(pc) (137KB) ( 384 )
An analytical expression of free induction decay has been derived for calculating the magic angle spinning sideband patterns of nuclear magnetic resonance spectra in a two-site exchange problem. The expression has been confirmed by comparing the calculated spinning sideband patterns for powdered crystalline dimethyl sulfone at different exchange rates with experimentally measured spectra at various temperatures.
Temperature Dependence of the Luminescence Decay Time of a PbWO4 Scintillator
SHI Chao-shu, DENG Jie, HAN Zheng-fu, XIE Zhi-jian, LIAO Jing-ying, G. Zimmerer, J. Beker, M. Kamada, M. Runne, A. Schrö, der
Chin. Phys. Lett. 1998, 15 (6): 455-456 .  
Abstract   PDF(pc) (182KB) ( 373 )
Experimental results are given for the temperature dependence of the decay time of the emission at 430nm from PbWO4 crystal under vacuum-ultraviolet (82nm) photon excitation in the temperature range of 80-300K. The structures in the curve are interpreted for the first time by studying the thermoluminescence of PbWO4, which originates from the traps in the crystal.

Cathodoluminescence of ZnO Films
FU Zhu-xi, GUO C hang-xin, LIN Bi-xia, LIAO Gui-hong
Chin. Phys. Lett. 1998, 15 (6): 457-459 .  
Abstract   PDF(pc) (225KB) ( 708 )
The cathodoluminescence of ZnO films deposited on Si substrates by reactive dc sputtering is investigated. Apart from the characteristic green emission band (522nm) of ZnO, an ultraviolet (392nm) band and a blue (430-460 nm) band have been observed. The x-ray diffraction and cathodoluminescent spectra reveal the dependences of the luminescence on the preparation conditions and crystallinity of the ZnO films.
Growth of Oriented Heteroepitaxial Diamond Films on Si(100) via Electron Emission in Hot Filament Chemical Vapor Deposition
WANG Wan-lu, LIAO Ke-jun, FENG Bin, ZHANG Zhi
Chin. Phys. Lett. 1998, 15 (6): 460-462 .  
Abstract   PDF(pc) (423KB) ( 620 )
The oriented heteroepitaxial diamond films were obtained on Si(100) substrate via electron emission in hot filament chemical vapor deposition with the orientation relationship of diamond < 100 >//Si< 100 > and < 110 > //Si< 110 >. The nucleation and subsequent growth of diamond films were characterized by scanning electron microscopy and Raman spectroscopy. The experimental results showed that the electron emission from the diamond coating on the electrode played a critical role during the nucleation due to excition plasma. The maximum value of nucleation density was up to 1011cm-2 on pristine Si surface at emission current of 250mA. The effect of the electron emission on the reactive gas composition was analyzed by in situ infrared absorption, indicating that the concentration of CH4 and C2H2 near the substrate surface was extremely increased. This may be responsible for the enhanced nucleation by electron emission.
Synchronized Oscillations in γ Frequency Band in a Neuronal Network
WANG Wei, CHEN Guang, LIU Feng
Chin. Phys. Lett. 1998, 15 (6): 463-465 .  
Abstract   PDF(pc) (266KB) ( 359 )
Synchronous oscillation with frequencies in γ band (30-70 Hz), regarded as relevant to the information processing such as scene segmentation, has been numerically studied in a neuronal network. It is found that this synchronous oscillation relates to an intrinsic oscillation of the system in γ band and this feature is robust to various configurations of external stimuli and couplings.
Influence of Solar Photogravitation on the Motion of Comet Hale-Bopp
ZHENG Xue-tang, ZHU Wen-yao, YU Li-zhong
Chin. Phys. Lett. 1998, 15 (6): 466-468 .  
Abstract   PDF(pc) (195KB) ( 464 )
On the basis of photogravitational theory, the influence of solar photogravitation on the motion of comet Hale-Bopp is discussed. It is shown that for plasma tail of comet Hale-Bopp there is only one collinear point L3 and for a few of dust tail there can be two coplanar points L6, L7 and three collinear points L21, L22, L3. The regions in which the coplanar points exist and the dust grain of comet Hale-Bopp can move are also obtained.
28 articles