网络环境下会计信息系统的创新

从我国会计软件的发展历程及网络环境方面，对会计信息系统软件功能的创新、会计信息系统基本结构的创新作了分析和探讨，提出了会计软件未来发展与创新的基本思路和设想．     

Measurement of Secular Motion Frequency in Miniature Paul Trap to Ascertain the Stability Parameters

40Ca＋ ions are trapped and laser cooled in a miniature Paul trap. The secular motion was observed by the radio-frequency resonance of the ion cloud and Zeeman profile sidebands of a single ion experimentally. The trap stability parameters a and q are determined with an uncertainty under 1% by the secular motion frequency measurement. The trap efficiency is 0.75. A practicable suggestion is given for the benefits of a new trap design.     

Improvement of Stability of ~(40)Ca~+ Optical Clock with State Preparation

Stability is one of most important performances of an atomic clock. Here we describe our recent work on improving the stability of our 40 Ca+ optical clock. State preparation is adopted to transfer the ion to the groundstate magnetic sublevel of the clock transition, after the quenching laser transfers the ion to the ground state at each cycle. Using this method,the stability for ~(40)Ca~+ optical clock is improved to about 6.3 × 10~(-15)/τ~(1/2).Compared with 1.0 × 10~(-14)/τ~(1/2) in previous work, the averaging time is decreased to reach a given level of statistical uncertainty in a clock comparison.     

高准确度的钙离子光频标

近年来,冷原子技术和激光技术促进了高精度光频标的发展,有望在建立时间基准、推动基础研究和满足国家需求等方面发挥重要的作用.本文介绍了中国科学院武汉物理与数学研究所近年来在高准确度钙离子(~(40)Ca~+)光频标研究方面的进展:采用新的ULE腔系统,实现了729 nm钟跃迁激光器1—100 s的频率稳定度均优于2×10~(-15),通过对外场和环境效应的控制及克服,特别是囚禁离子运动效应的抑制,获得单个钙离子光频标的不确定度优于5.5×10~(-17);通过两台光频标的比对,测得20000 s的稳定度也进入10~(-17)量级;基于高精度钙离子光频标平台,进行了相关精密测量的工作,包括:基于全球定位系统的超高精度远程光频绝对值测量方案,第二次测量了钙离子的光频跃迁绝对值,该测量结果再次被国际时间频率咨询委员会采纳,更新了钙离子的频率推荐值;精确测量了钙离子的钟跃迁魔幻波长,由此提出新型的全光囚禁离子光频标的方法;精密测量了钙离子的亚稳态寿命等参数.以上工作推动了基于冷原子的精密测量工作.     

高精度可搬运钙离子光钟

时间的计量一直是人们所关心的基本问题,它与人们的日常生产生活息息相关。随着科学技术的发展与进步,人类对时间的计量也越来越精确。近年来,光钟已经成为当前世界上最精确的计时工具。然而,往往因体积庞大、仅能在实验室环境工作,极大地限制了光钟的应用范围。实现可搬运、可靠、准连续运行的高精度光钟是科学家的愿望,也是对光钟科研工作者的挑战。文章将简单介绍光钟的原理,然后介绍可搬运钙离子光钟的研究进展,最后浅谈可搬运原子光钟的未来发展。     

光钟的发展和应用

正原子频标(原子频率标准的简称)是利用量子力学原理制成的高稳定度和高准确度的频率、时间信号产生系统(成为一个装置时又称为原子钟)。通俗地说,原子钟就像一个计时器一样,记录着时间的流逝。而今天所说的光钟,作为原子钟的一员,顾名思义,就是利用光学频率作参考的原子钟。古语云:一日不见,如隔三秋;当描述人很紧张或难过,常用"度日如年"来形容;当我们很兴     

Quantitative evaluation of space charge effects of laser-cooled three-dimensional ion system on a secular motion period scale

In this paper,we introduce a method of quantitatively evaluating and controlling the space charge effect of a lasercooled three-dimensional(3 D) ion system in a linear Paul trap.The relationship among cooling efficiency,ion quantity,and trapping strength is analyzed quantitatively,and the dynamic space distribution and temporal evolution of the 3 D ion system on a secular motion period time scale in the cooling process are obtained.The ion number influences the eigen-micromotion feature of the ion system.When trapping parameter q is ~ 0.3,relatively ideal cooling efficiency and equilibrium temperature can be obtained.The decrease of axial electrostatic potential is helpful in reducing the micromotion heating effect and the degradation in the total energy.Within a single secular motion period under different cooling conditions,ions transform from the cloud state(each ion disperses throughout the envelope of the ion system) to the liquid state(each ion is concentrated at a specific location in the ion system) and then to the crystal state(each ion is subjected to a fixed motion track).These results are conducive to long-term storage and precise control,motion effect suppression,high-efficiency cooling,and increasing the precision of spectroscopy for a 3 D ion system.     

A snapback-free TOL-RC-LIGBT with vertical P-collector and N-buffer design

A reverse-conducting lateral insulated-gate bipolar transistor(RC-LIGBT) with a trench oxide layer(TOL), featuring a vertical N-buffer and P-collector is proposed. Firstly, the TOL enhances both of the surface and bulk electric fields of the N-drift region, thus the breakdown voltage(BV) is improved. Secondly, the vertical N-buffer layer increases the voltage drop VPNof the P-collector/N-buffer junction, thus the snapback is suppressed. Thirdly, the P-body and the vertical N-buffer act as the anode and the cathode, respectively, to conduct the reverse current, thus the inner diode is integrated. As shown by the simulation results, the proposed RC-LIGBT exhibits trapezoidal electric field distribution with BV of 342.4 V, which is increased by nearly 340% compared to the conventional RC-LIGBT with triangular electric fields of 100.2 V. Moreover,the snapback is eliminated by the vertical N-buffer layer design, thus the reliability of the device is improved.     

Snapback-free shorted anode LIGBT with controlled anode barrier and resistance

A novel shorted anode lateral-insulated gate bipolar transistor(SA LIGBT)with snapback-free characteristic is proposed and investigated.The device features a controlled barrier V_barrierand resistance R_SAin anode,named CBR LIGBT.The electron barrier is formed by the P-float/N-buffer junction,while the anode resistance includes the polysilicon layer and N-float.At forward conduction stage,the V_barrierand R_SAcan be increased by adjusting the doping of the P-float and polysilicon layer,respectively,which can suppress the unipolar mode to eliminate the snapback.At turn-off stage,the low-resistance extraction path(N-buffer/P-float/polysilicon layer/N-float)can quickly extract the electrons in the N-drift,which can effectively accelerate the turn-off speed of the device.The simulation results show that at the same V_on of 1.3 V,the E_offof the CBR LIGBT is reduced by 85%,73%,and 59.6%compared with the SSA LIGBT,conventional LIGBT,and TSA LIGBT,respectively.Additionally,at the same Eoffof 1.5 m J/cm²,the CBR LIGBT achieves the lowest V_on of 1.1 V compared with the other LIGBTs.     

控制光场的原子钟

2013年1月出版的Physics Today杂志刊登了法国法兰西学院教授、诺贝尔奖获得者塞尔日·阿罗什(Serge Haroche)等的专题文章.文章描述了Ramsey干涉仪作为一种非破坏性探测的工具,用于探测单光子的产生和湮灭,通过伺服回路反馈制备光子的量子态,以及通过原子和光子的纠缠实现薛定谔猫态. 2011年12月逝世的Norman Ramsey 于1949年发明了分离场原子干涉仪,从而引起了时间测量的革命.该技术最初被用于分子束磁共振谱测量实验,提高了测量的分辨率.后来,Ramsey干涉仪被广泛应用于原子钟,在很大程度上提高了原子钟的精度.