A scheme to generate the two-mode field entangled states is proposed, based on the Raman interaction of an effective two-level atom with the pump and Stokes fields. The degree of the entanglement between the two field modes in the entangled states is also studied.

The Larmor precession of a spinning particle in a magnetic field confined in the region of one dimensional-rectangular barrier is investigated with the spin coherent state of incoming particle, which has advantage to recognize the equation of the spin precession. Our new observation is that the precession time of spin is uniquely determined and is seen to be equal to the dwell time.

Bifurcation control has attracted increasing attention in recent years. A simple and unified state-feedback method is developed in this paper for Hopf bifurcation control for continuous-time systems. The control task can be eit her shifting an existing Hopf bifurcation or creating a new Hopf bifurcation. Some computer simulations are included to illustrate the method and verify the theoretical results.

The nonrelativistic energies of the 1s^{2}nd and 1s^{2}nf(n=6, 7, 8 and 9) states for the lithium isoelectronic sequence from Li I to Ne VⅢ are calculated by using a full core plus correlation method with multiconfiguration interaction wave function. Relativistic and mass-polarization effects on the energy are evaluated as the first-order pertur bation theory. In most cases with nuclear charge, Z≤7, the agreement between our predicted excitation energies and the experimental data is less than 1cm^{-1}.

A three-parameter nonlinear dynamical model, i.e., the quantized discrete self-trapping equation, was used to calculate the highly excited CH stretching vibrational energy levels of liquid phase CH_{3}CN molecule in the electronic ground state up to n=7. The calculated results show that the experimental energy levels can be well described by the model.

Accurate reactive scattering calculations of reactive probabilities and integral cross sections for the system D+H_{2}→DH+H were carried out by using the quantum mechanical time-dependent wave packet methods. In order to simplify the calculation, we introduced the centrifugal sudden approximation to reduce the effective degrees of freedom, and show results of new calcul ations. In particular, the present calculations were extended to all angular momentum and obtained reaction cross sections for a range of energies. The results were also compared with those of other theoretical calculations and the differences were discussed.

An interferometric detection scheme to measure optical phase shift with sensi tivity beyond the shot noise limit is proposed. The theoretical calculation shows that using the quantum correlated twin beams produced from an optical parametric amplifier as the input fields of a Mach-Zehnder interferometer, the minimum detectable phase shift will exceed the shot noise limit N^{-1/2} and approach the Heisenberg limit N^{-1}. The parametric dependences of the minimum detectable phase shift on the nonlinear interaction, input photon number, and detection efficiency are shown.

A new scheme of electromagnetically induced two-photon transparency in a four-level V-type Doppler-broadened medium is presented in this paper. Under a proper condition, the two-photon absorption can be greatly reduced by applying a control laser field with relatively lower intensity compared with that needed in other field-induced multi-photon absorption reduction.

From transition-rate-equations and transmission-equations the formulas of threshold power and slope efficiency of an end-pumped laser for a four-level system are deduced. Citing the laser of Er:YAG as an example, we have discussed the differences of laser output characteristics between the three-and four-level systems.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

The σ-T and dσ/dT-T curves of the FeCuNbSiB amorphous alloy, which are the relationship between "apparent weight loss" and tempera ture, are investigated by magnetic thermogravimetry analysis (MTGA) technique. It is found that the crystallization process of the samples can be divided into five stages. The studies of samples annealed in the temperature range of 480-610℃ for 1 h show that when the annealing temperature (T_{a}) is lower than 540℃, the quantity of nanocrystalline α-Fe(Si) phase increases evidently with T_{a}, and the Curie temperature (T_{c}) of residual amorphous phase also increases linearly with T_{a}, i.e., T_{c}=0.52T_{a}+91.7℃, with correlation coefficient γ=0.98. The variation of volume fraction of α-Fe(Si) nanocrystalline phase or residual amorphous phase with T_{a} is measured.

Li Yu-tong, Gu Yu-qiu, Li Ying-jun, Zhang Jie, Chun-yu Shu-tai, You Yong-lu, He Shao-tang, Huang Wen-zhong, He Ying-ling, Lu Li-zhu, Yuan Xiao-dong, Wei Xiao-feng, Zhang Chuan-fei

Chin. Phys. B 1999, 8 (6): 0463; doi: 10.1088/1004-423X/8/6/011
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A comparison has been made of performance of the neon-like chromium soft X-ray lasing at 28.5 nm driven by a double 900 ps pulse at 6 TW/cm^{2}, with that driven by a double 200 ps pulse at similar irradiance. The double 200 ps pulse has been found to be much more efficient to drive X-ray lasing with higher intensity.

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