非线性囚禁离子模型中振幅平方压缩效应

本文从非线性Jaynes-Cummings模型出发, 研究了受驻波场驱动的离子的质心运动振幅平方压缩效应.结果表明, 非线性参数η对压缩效应有明显的影响. 随着参数η的增大, 离子处于压缩态的时间增长, 压缩程度加深, 但当η越过某一临界值时, 离子最大压缩量减小, 压缩时间相对变短;另外, 驻波场的相位也对压缩效应有明显的影响.     

囚禁离子的非线性Jaynes-Cummings模型及其布居数反转演化

从描述囚禁离子与驻波激光场相互作用的Jaynes-Cummings(J-C)模型出发，导出了囚禁离子谐振动单量子共振激发相互作用的非线性J-C模型. 通过求解这一模型的系统状态随时间变化，数值研究了离子布居数反转的演化规律. 结果表明，离子布居数反转演化的崩塌-复原周期与Lamb-Dick参数η和离子在驻波激光场中的位置有关，随着η参数的增大，离子布居数反转的崩塌-复原周期变短，当离子质心的位置从驻波激光场的波节移向波腹时，离子布居数崩塌-复原的周期变长. 关键词： 驻波激光场 囚禁离子 非线性J-C模型 Lamb-Dick参数     

非线性增光子热态的非经典特性

本文从描述驻波激光场与囚禁离子相互作用的非线性Jaynes-Cummings模型出发,引入一种新的量子态,即非线性增光子热态.采用理论分析和数值计算相结合的方法,研究了Lamb-Dicke参数,温度和激光场的初相位等参数对这种量子态的非经典效应的影响.结果表明:非线性增光子热态的Mandel Q因子随温度的变化存在一个极小值.Lamb-Dicke参数越大,非线性增光子热态的非经典效应就越强.此外驻波场的初相位也对该态的非经典效应有明显的影响.     

囚禁离子在大失谐双色驻波场中的崩塌-回复特性

讨论了囚禁离子与两驻波场相互作用时的量子相干性.在大失谐的条件下,离子的振动能量呈现崩塌-回复的相干性特征,表明离子的振动态具有压缩效应.无量纲压缩参数G3愈大,囚禁离子的振动态压缩效应愈显著.进一步增大参数G3,所能得到的最大压缩反而减小.     

囚禁离子非线性Jaynes-Cummings模型量子场熵演化特性

利用VonNeuuman量子约化熵理论研究了驻波激光场与囚禁在谐振势中的离子单量子共振相互作用系统中量子场熵的时间演化特性,通过数值计算详细讨论了Lamb-Dick参数、离子质心在驻波激光场中的位置以及囚禁离子初始状态对量子场熵演化特性的影响.结果表明:Lamb-Dick参数影响囚禁离子与驻波激光场之间量子纠缠的频率和幅度,其值越大离子与光场之间的平均纠缠程度越低;随着离子质心从驻波激光场的波节向波腹移动,二者之间量子纠缠的振荡频率逐渐变慢,纠缠强度逐渐减弱;随着囚禁离子处于激发态概率的减小,离子与光场之间的量子纠缠呈现先增强后减弱的变化趋势.这些特性对于纠缠态的制备以及利用囚禁离子进行量子通讯等信息处理过程有一定的参考价值.     

驻波激光场中囚禁离子的线性熵和量子态转移研究

运用量子纠缠和线性熵理论,研究了驻波激光场中囚禁离子的线性熵和量子态转移.讨论了相干角、离子的相对位相、离子与驻波激光场之间的耦合强度以及失谐量、Lamb-Dicke参数对离子线性熵的影响.结果表明,在一定的条件下可以实现囚禁离子的内态到振动态的相干转移,线性熵随时间的演化呈现非周期性的振荡行为.离子线性熵的最大值随着相干角、离子与激光场之间的耦合强度以及失谐量的增大而减小,随着Lamb-Dicke参数的增大而增大.并且可以通过调节驻波激光场来调节离子与驻波激光场之间的耦合强度和失谐量,从而达到对离子线性熵的控制与操纵,理论上提供了一种调控纠缠的方式.     

驻波激光场中囚禁离子的线性熵和量子态转移研究

运用量子纠缠和线性熵理论,研究了驻波激光场中囚禁离子的线性熵和量子态转移。讨论了相干角、离子的相对位相、离子与驻波激光场之间的耦合强度以及失谐量、Lamb-Dicke参数对离子线性熵的影响。结果表明,在一定的条件下可以实现囚禁离子的内态到振动态的相干转移,线性熵随时间的演化呈现非周期性的振荡行为。离子线性熵的最大值随着相干角、离子与激光场之间的耦合强度以及失谐量的增大而减小,随着Lamb-Dicke参数的增大而增大。并且可以通过调节驻波激光场来调节离子与驻波激光场之间的耦合强度和失谐量,从而达到对离子线性熵的控制与操纵,理论上提供了一种调控纠缠的方式。     

驻波激光场中囚禁离子内外自由度熵的演化特性

从描述囚禁离子与驻波激光场相互作用的Jaynes-Cummings（J-C）模型出发,导出了囚禁离子谐振动单量子共振激发相互作用的非线性J-C模型。通过求解这一模型下系统态和离子系统熵的演化规律,数值研究了囚禁离子的熵演化与Lamb-Dick参数  、离子在驻波激光场中的位置以及初始声子强度之间的关系。结果表明,离子熵的演化呈现非周期性的振荡。随着参数  的增大,囚禁离子熵演化的振荡频率变大,囚禁离子内外自由度退纠缠的时间变短。当离子质心的位置从驻波激光场的波节移向波腹,囚禁离子熵演化的振荡频率变小,离子与声子自由度退纠缠的时间变长。如果初始声子场强度较小,离子熵随时间的演化强烈地表现为不规则的振荡,且振荡频率较大;随着初始声子场强度变大,离子熵的演化类似于J-C模型中的场熵演化,不规则的振荡频率逐渐变小。     

捕陷原子在大失谐双色场中的量子崩塌-回复特性

分析了捕陷的二能级原子在大失谐条件下与驻波光场和行波光场共同作用时的动力学.原子的量子平均能量随时间的变化呈现崩塌-回复的特征,表明这个系统的振动态具有压缩效应.系统的非线性(参数μ)越大,崩塌-回复的频率越大,离子的量子平均能量越小.随着行波场强的增大,冷却原子的振动态压缩效应愈显著. 关键词：     

脉冲式棘齿势场作用下囚禁离子的规则与混沌运动

考虑赝势近似下囚禁于Paul阱中的单离子与由脉冲式双激光驻波构成的棘齿势场的相互作用.应用积分方程方法得到系统的经典运动精确解，通过数值方法作出相空间轨道并计算由平均速度定义的流，结合分析与数值结果研究囚禁离子的规则与混沌运动特性.与单驻波型激光脉冲情形相比，发现两个重要的棘齿效应：一是脉冲式棘齿势场的作用导致参数空间混沌区域的改变，从而适当调节第二驻波参数，可使离子的规则运动变为混沌运动，或者混沌运动变为规则运动；二是通过分析平均流随激光参数的变化，发现棘齿势场的介入能使囚禁离子作平均意义下的单向输运，随着势场强度增加到混沌区域，流的强度明显减小并改变方向，系统进入混沌运动. 关键词： 脉冲式棘齿势 囚禁离子 混沌 输运     

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.     

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.     

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.