碱金属原子多极极化率的解析计算及其应用

通过考虑碱金属原子中的价电子在模型势中的运动, 给出了碱金属原子激发态(包括分立谱和连续谱)的波函数, 导出了碱金属原子的多极动态极化率的计算式中所涉及的矩阵元的解析表达式, 实现了碱金属原子多极动态极化率的解析计算. 作为应用, 利用范德瓦尔斯相互作用系数与动态极化率之间的积分关系, 计算了异核基态碱金属原子间的三体相互作用系数, 将计算结果与此前用稳定变分方法得到的结果进行了比较, 结果显示两者是一致的. 此工作为后续研究激发态碱金属原子间的相互作用奠定了基础.     

Calculations of the dynamic dipole polarizabilities for the Li~+ ion

The B-spline configuration-interaction method is applied to the investigations of dynamic dipole polarizabilities for the four lowest triplet states(2~3S,3~3S,2~3P,and 3~3P) of the Li~+ ion.The accurate energies for the triplet states of n~3S,n~3P,and n~3D,the dipole oscillator strengths for 2~3S(3~3S)→n~3P,2~3P(3~3P)→n~3S,and 2~3P(3~3P)→n~3D transitions,with the main quantum number n up to 10 are tabulated for references.The dynamic dipole polarizabilities for the four triplet states under a wide range of photon energy are also listed,which provide input data for analyzing the Stark shift of the Li~+ ion.Furthermore,the tune-out wavelengths in the range from 100 nm to 1.2 μm for the four triplet states,and the magic wavelengths in the range from 100 nm to 600 nm for the 2~3S→3~3S,2~3S→2~3P,and 2~3S→3~3P transitions are determined accurately for the experimental design of the Li~+ ion.     

Dynamic polarizabilities of the clock states of Al+

The dynamic polarizabilities of ${\rm 3s}^2\,^1{\rm S}_0$ and ${\rm 3s}{\rm 3p}\,^3{\rm P}_0^{\rm o}$ states of Al$^+$ are calculated using the hybrid configuration interaction and many-body perturbation theory method, and multiconfiguration Dirac-Hartree-Fock method in this work. Five ultraviolet magic wavelengths for the Al$^+$ clock transition ${\rm 3s}^2\,^1{\rm S}_0$-${\rm 3s3p}\,^3{\rm P}_0^{\rm o}$ are predicted. Although the suitable lasers are not available presently, the potential precision measurement on these magic wavelengths for the Al$^+$ clock transition would be used to extract the ratios of several certain transition matrix elements with high accuracy, and then help to improve the precision and reliability of the estimate of the BBR shift of the Al$^+$ clock transition. The differential dynamic polarizabilities at certain wavelengths are evaluated, which are useful to assess the ac Stark shift of the Al$^+$ clock transition frequency and helpful in the clock experiments to suppress the ac Stark shift of the clock transition as possible as it can.     

Improvement of the short-term stability of atomic fountain clock with state preparation by two-laser optical pumping

To improve the signal to noise ratio(SNR) and the short-term stability of cesium atomic fountain clocks, the work of two-laser optical pumping is presented theoretically and experimentally. The short-term stability of the NIM6 fountain clock has been improved by preparing more cold atoms in the |F = 4, mF= 0〉 clock state with a shortened cycle time.Two π-polarized laser beams overlapped in the horizontal plane have been applied after launching, one is resonant with|F = 4〉→ |F = 4〉 transition and the other is resonant with |F = 3〉→ |F = 4〉 transition. With optical pumping, the population accumulated in the |mF= 0〉 clock state is improved from 11% to 63%, and the detection signal is increased by a factor of 4.2, the SNR of the clock transition probability and the short-term stability are also improved accordingly.     

Evaluation of the frequency instability limited by Dick effect in the microwave ~(199)Hg~+ trapped-ion clock

In the microwave ~(199)Hg~+ trapped-ion clock, the frequency instability degradation caused by the Dick effect is unavoidable because of the periodical interrogating field. In this paper, the general expression of the sensitivity function g(t)to the frequency fluctuation of the interrogating field with Nπ-pulse(N is odd) is derived. According to the measured phase noise of the 40.5-GHz microwave synthesizer, the Dick-effect limited Allan deviation of our ~(199)Hg~+ trapped-ion clock is worked out. The results indicate that the limited Allan deviations are about 1.75 × 10~(-13)τ~(1/2) and 3.03 × 10~(-13)τ~(1/2) respectively in the linear ion trap and in the two-segment extended linear ion trap under our present experimental parameters.     

用ISP器件进行可编程数字钟逻辑电路设计的研究

采用自行研制的基于ISP器件的数模两用仿真开发系统和ispEXPERT设计软件，利用层次化管理混合输入方式设计的方法，实现了可编程数字钟逻辑电路的设计。     

Theoretical calculations on Landé $g$-factors and quadratic Zeeman shift coefficients of $n$s$n$p $^{3} {P}^{o}_{0}$ clock states in Mg and Cd optical lattice clocks

The study of magnetic field effects on the clock transition of Mg and Cd optical lattice clocks is scarce. In this work, the hyperfine-induced Landé $g$-factors and quadratic Zeeman shift coefficients of the ${n{\rm s}n{\rm p}}$ $^3P^{\rm o}_0$ clock states for $^{111,113}$Cd and $^{25}$Mg were calculated by using the multi-configuration Dirac-Hartree-Fock theory. To obtain accurate values of these parameters, the impact of electron correlations and furthermore the Breit interaction and quantum electrodynamical effects on the Zeeman and hyperfine interaction matrix elements, and energy separations were investigated in detail. We also estimated the contributions from perturbing states to the Landé $g$-factors and quadratic Zeeman shift coefficients concerned so as to truncate the summation over the perturbing states without loss of accuracy. Our calculations provide important data for estimating the first- and second-order Zeeman shifts of the clock transition for the Cd and Mg optical lattice clocks.     

Blackbody radiation shift of the Al<Superscript>+</Superscript> clock transition

The blackbody radiation shift of the Al⁺ 3s^{2 1}S^e ₀ ↦ 3s3p ³P^○ ₀ clock transition is evaluated. The polarizabilities of the two states are determined by means of configuration interaction calculations in conjunction with oscillator strength sum rules. The ground state polarizability was 24.14 ±0.12 a.u. while the metastable state polarizability was 24.62 ±0.25 a.u. The derived frequency shift at 300 K was Δν= -0.0042 ±0.0032 Hz. Some auxiliary sum rules are evaluated that allow for the conversion of a finite frequency polarizability difference to a static polarizability difference.     

Ab initio study of the EFG tensor at Cd impurities in Sc2O3 semiconductor

We present an ab initio study of diluted Cd impurities localized at both cation sites of the semiconductor Sc₂O₃. The electric-field-gradient (EFG) tensor at Cd impurities located at both cationic sites of the host structure was determined from the calculation of the electronic structure of the doped system. Calculations were performed with the full-potential augmented-plane wave plus local orbitals (APW+lo) method within the framework of the density functional theory. We studied the atomic structural relaxations and the perturbation of the electronic charge density induced by the impurities in the host system in a fully self-consistent way. We showed that the Cd impurity introduces an increase of 8% in the nearest oxygen neighbors bond-lengths, changing the EFG sign for probes located at the asymmetric cation site. The APW+lo predictions for the charged state of the Cd impurity were compared with EFG results existent in the literature, coming from time-differential γ–γ perturbed-angular-correlations experiments performed on ¹¹¹Cd-implanted Sc₂O₃ powder samples. From the excellent agreement between theory and experiment, we can strongly suggest that the Cd acceptor impurities are ionized at room temperature. Finally, we showed that simple calculations like those performed within the point-charge model with antishielding factors do not correctly describe the problem of a Cd impurity in Sc₂O₃.     

Laser-induced fluorescence study of the influence of N <Emphasis Type="Bold">2</Emphasis> and CH <Emphasis Type="Bold">4</Emphasis> on the <Emphasis Type="Bold">114</Emphasis>Cd intercombination line

Using a laser-induced fluorescence method a detailed analysis of profiles of the ¹¹⁴Cd 326.1 nm line perturbed by N₂ and CH₄ was performed which revealed deviations from the ordinary Voigt profile. These deviations are shown to be consistent with fits of experimental profiles to an asymmetric Voigt profile. Coefficients of the pressure broadening, shift and collision-time asymmetry are determined and compared with those calculated for van der Waals interaction potential. Received 29 November 2001 / Received in final form 12 July 2002 Published online 4 February 2003