周期驱动玻色-爱因斯坦凝聚系统的棘齿效应

研究了周期脉冲驱动下的玻色-爱因斯坦凝聚体系（BEC）的动力学演化.其中着重考虑了BEC原子间的非线性相互作用对量子棘齿效应的影响.数值计算结果表明,较弱的非线性相互作用可以减弱定向动量流的强度.而较强的非线性相互作用则会使量子棘齿效应消失甚至发生反转,即系统会出现反向的定向动量流,而且随着时间的演化,动量流会表现出微弱的饱和趋势.计算还发现,高阶量子共振下系统的棘齿效应变得很不明显,而且外部驱动势的周期噪声很容易破坏体系的棘齿效应. 关键词： 玻色-爱因斯坦凝聚 量子混沌 量子共振 棘齿效应     

广义Fibonacci时间准周期量子行走波包扩散的动力学特性

本文通过数值计算的方法研究了一维离散时间准周期量子行走的动力学特性,主要研究了两个自旋空间C算符按照广义Fibonacci准周期排列的量子行走,发现对两类广义Fibonacci准周期序列,波包扩散都是超扩散(即标准方差σ约为t~γ,0.5γ1),而且在给定的两个C算符下,第二类广义Fibonacci准周期序列的幂指数γ大于第一类广义Fibonacci准周期序列.通过对波包扩散的概率分布情形和标准方差的研究发现,第一类广义Fibonacci准周期序列的波包扩散更接近于经典随机行走(γ=0.5),而第二类广义Fibonacci准周期序列的波包扩散更接近于均匀量子行走(γ=1),这与两类广义Fibonacci准周期量子自旋链中量子相变时的特性相反.     

矩形弹子球中的量子波包分析(英文)

利用波包分析量子力学体系的动力学行为在研究经典和量子的对应关系方面越来越成为一个非常重要的方法.利用高斯波包分析方法,我们计算了矩形弹子球体系的自关联函数,自关联函数的峰和经典周期轨道的周期符合的很好,这表明经典周期轨道的周期可以通过含时的量子波包方法产生.我们还讨论了矩形弹子球的波包回归和波包的部分回归,计算结果表明在每一个回归时间,波包出现精确的回归.对于动量为零的波包,初始位置在弹子球内部的特殊对称点处,出现一些时间比较短的附加的回归.     

注入原子相干性对双模MAZER的影响

首先简单介绍超冷原子注入的微脉塞(MAZER)的基本理论和研究进展,然后具体介绍我们目前关于超冷V型三能级原子注入的双模微脉塞(双模MAZER)的研究工作.我们研究了原子相干性对这种双模MAZER系统中原子的发射几率和原子通过腔的透射几率的影响.结果表明,原子的发射几率随腔长变化的曲线中存在共振峰和非共振平台;当两个模的耦合强度之比一定时,不同注入原子相干性对应的发射几率共振峰呈现出相当大的区别.在原子透射几率随原子动量的变化曲线中也存在共振峰和非共振平台.腔长对原子的速度具有选择性,当腔长给定时,通过适当选择原子的相干参量,可调节原子通过腔的透射几率,从而可对原子的速度进行选择.     

氢负离子在梯度电场中光剥离的波包动力学研究

利用含时微扰论和闭合轨道理论相结合的方法, 给出了氢负离子在梯度电场中自关联函数的计算公式, 并且对体系的自关联函数进行了计算和分析. 重点探讨了激光脉冲的宽度、梯度电场中背景电场强度及电场梯度对氢负离子体系的自关联函数的影响. 研究结果表明, 当激光脉冲的脉冲宽度较短, 远小于剥离电子的闭合轨道的周期时, 量子波包的回归现象显著, 自关联函数中会出现一系列比较明显的回归峰, 这是由于沿闭合轨道返回的电子波包和出射的电子波包之间产生干涉形成的. 但是随着激光脉冲宽度的增加, 量子波包的回归现象减弱. 当脉冲宽度和闭合轨道的周期相差不是很大时, 自关联函数中的回归峰逐渐变宽, 振荡渐趋平缓, 相邻的峰之间发生相互干涉, 从而导致对应关系消失. 除此之外, 我们还发现梯度电场中背景电场强度和电场梯度对体系的自关联函数也会发生显著的影响. 随着背景电场强度和电场梯度的增加, 剥离电子的闭合轨道的周期变短, 自关联函数中回归峰的个数逐渐增加, 量子回归现象增强. 因此, 我们可以通过改变脉冲的宽度、外加电场强度的大小对氢负离子发生光剥离的自关联函数进行调控. 我们的结果对于实验研究原子或离子体系在外场中的波包动力学性质可以提供一定的参考价值.     

原子质心运动的量子效应对光场量子噪声压缩的影响

考虑JaynesCummings模型中与光场相互作用的原子为超冷原子,讨论了原子质心运动的量子效应对光场两正交分量量子噪声压缩的影响,结果表明,在JaynesCummings模型中,原子质心运动的量子效应增加光场两正交分量的量子噪声,使其压缩效应消失 关键词： 超冷原子 质心运动的量子效应 光场量子噪声压缩     

一维谐振子量子运动中的经典特性

利用量子力学的态叠加原理和算符劈裂法,对处于一维谐振子势中的初始态为高斯波包的中心位置的量子运动进行了研究.结果表明:其中心位置的量子运动呈现出经典谐振子的运动特性;波包的初始位置和初始时刻所加动量对波包中心位置量子动力学的影响与经典谐振子类似条件对运动的影响有相同的性质.本结果对理解复杂量子运动中的高斯波方法有一定的启示作用.     

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研究了电漂移对通行高能离子与新经典撕裂模(NTM)共振相互作用的影响。利用漂移动力论方法,在求解共振相互作用产生的作用在磁岛上的环向力矩的过程中重新考虑了电漂移的作用。结果表明,在与磁岛运动相关的环向动量平衡中v>0的通行高能离子与v<0的通行高能离子作用恰好相反,当磁岛沿电子抗磁漂移方向传播时,前者趋向于使磁岛传播频率减小,后者趋向于使磁岛传播频率增大,通行高能离子产生的总的环向力矩几乎为零。仅将v>0的通行高能离子所产生的环向力矩带入由环向动量平衡方程和修正的卢瑟福方程所组成的方程组中,数值计算结果表明,描述磁岛旋转频率与宽度随时间做非线性振荡的稳定极限环并不存在。     

具有原子相干性的超冷V型三能级原子注入的双模微脉塞的透射几率

建立了超冷V型三能级原子注入的双模微脉塞的透射几率的量子理论，研究了原子相干性对透射几率的影响。发现原子的透射几率随原子质心动量的变化曲线中存在着共振峰和非共振平台。给定腔长，通过调节原子相干参量和原子的二个跃迁通道的耦合强度，可以改变这些共振峰和非共振平台的性质。     

超冷V型三能级原子注入的微波激射:原子相干性对腔场光子统计的影响

建立了超冷V型三能级原子注入的微波激射的腔场光子统计的量子理论,研究了原子相干性对光子统计性质的影响.发现腔内原子的发射概率随腔长变化的曲线中存在着共振峰和非共振平台,原子相干性对这些共振峰和非共振平台的绝对大小和相对比例具有灵活的可调性.原子发射概率的这些特点对腔场光子统计产生了直接的影响.平均光子数随腔长变化的曲线中也存在着共振峰和非共振平台;给定腔长,适当调节原子相干参量,可以使光子数分布向大、小光子数两个方向灵活地移动,平均光子数也相应地增加和减少.研究中还发现,适当选取原子相干参量,光子统计在大 关键词： 微波激射 超冷V型三能级原子 原子相干性 光子统计     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.