N+2原子受简并双光子作用时的纠缠动力学

研究了N+2（其中N个原子与光场非共振作用,2个原子与光场共振作用）原子受简并双光子作用的纠缠动力学,得到2个共振原子的纠缠度的解析表达式。结果表明：在简并双光子作用下,纠缠度的时间演化出现有规则的崩塌回复现象,并且崩塌回复周期比单光子作用下时要短。此外,N+2原子与光场间的相对耦合系数对简并双光子情形下的纠缠度有更灵敏的影响。     

Kerr介质中纠缠原子与非简并双光子相互作用的动力学

考虑了在位于充满Kerr介质的腔中,一对纠缠的二能级原子之一与非简并双光子的相互作用,当该原子离开腔被作选测性测量时,分析测量后光场的量子性质,研究结果表明,在纠缠度一定时,Kerr效应使光场平均光子数的崩塌回复周期减小,光场的二阶相干度减弱,使Cauchy-Schwartz不等式关联程度减弱.     

共振和非共振情况下非简并双光子Tavis-Cummings模型中原子与原子之间的纠缠演化

针对共振和非共振情况讨论了非简并双光子Tavis-Cummings(T-C)模型中原子与原子之间的纠缠演化,得到纠缠度的解析表达式.基于两类型不同的初态,详细分析了光场本征频率、原子跃迁频率以及原子与原子间偶极相互作用对纠缠的影响,并比较了共振和非共振情况下的纠缠演化行为.     

与原子依赖强度耦合双模压缩真空态的量子纠缠

在考虑原子与双模光场依赖强度耦合双光子共振相互作用的条件下,应用量子相对熵研究了双模压缩真空场模间纠缠度的演化.结果表明,在原子与光场相互作用之后,模间纠缠度作周期性的变化.在强场条件下,模间纠缠度总是在初始时刻达到最大值,其变化幅度基本保持不变.在初始场很弱的条件下,纠缠度演化的特点与原子初始状态有关,当原子处于激发态和基态的等概率叠加态时,纠缠度变化的幅度最大.控制原子与光场的作用时间及原子的初态,可以调整双模光场间的纠缠.     

两纠缠原子与光场相互作用系统场熵演化特性

研究了两纠缠原子与相干态光场相互作用系统场熵的时间演化特性,运用全量子力学理论和数值方法,讨论了初始两原子所处的纠缠状态、纠缠度和腔内光场的强弱对场熵的影响.随着光场平均光子数的增加,系统场熵均值和振荡频率增大;光场较弱时,场熵呈现一定的周期性振荡;光场增强后,场熵呈现出周期性的崩塌与回复,且随初始两原子纠缠度的增加,场熵的振幅增大.     

Bell态原子与双模纠缠相干光场相互作用系统的原子布居数演化

运用全量子理论并结合数值计算方法,研究了处于Bell态的两个全同二能级纠缠原子与双模纠缠相干光场相互作用系统的原子布居数演化特性.讨论了双原子体系的初态、光场的平均光子数、双模纠缠相干光场的纠缠程度以及双原子体系的原子间耦合强度对原子布居时间演化的影响.结果表明:双原子体系的初态为|β11〉时,原子布居数不随时间变化;初态为|β00〉、|β01〉和|β10〉时,当初始平均光子数增大到一定数值时演化特性呈现出周期性的崩塌和回复效应,随初始光子数的增加时间演化曲线的振荡频率增大振幅减小,且初态为|β00〉或|β10〉时原子布居的回复周期是初态为时|β01〉的两倍;双模纠缠相干光场的纠缠程度以及原子间偶极相互作用的强弱对Rabi振荡频率没有影响但对振幅有着显著的影响.     

频率变化的光场对双J-C模型中原子-原子纠缠的调控

本文研究了频率随时间变化的光场对双J-C模型中原子--原子纠缠的动力学调控, 主要讨论了光场频率随时间作正弦变化和脉冲变化两种典型情况下, 原子--原子纠缠度随时间的演化特性. 当光场频率随时间作正弦变化时, 原子--原子纠缠度演化的周期、振幅与光场频率调制的振幅有关, 并随着调制振幅的增强而减小. 光场频率的正弦调制和脉冲调制均能使光场与原子的相互作用模式在共振和非共振之间发生变化, 直接影响原子--原子纠缠度的演化规律. 通过光场频率的调制可以实现原子--原子纠缠度的提高与稳定, 避免ESD现象的出现, 从而达到动态调控原子--原子纠缠的目的.     

双模纠缠相干光与Bell态原子系统的光子统计

运用全量子理论并结合数值计算方法,研究了处于Bell态的两个全同二能级纠缠原子与双模纠缠相干光场相互作用系统的光子统计性质.分析了双原子体系的初态、光场的平均光子数、双模纠缠相干光场的纠缠程度以及双原子体系的原子间耦合强度对双模光场的光子统计性质的影响.结果表明：双原子体系的初态为｜β00〉、｜β10〉时,光场在其演化过程中不出现光子的反聚束效应；而当原子初态为｜β01〉或｜β11〉时,在一定的条件下可出现光子的反聚束效应.并且在光场的演化过程中,光子的反聚束效应出现的次数、时间和深度极其敏感地依赖于初始光场的平均光子数,而受到双模纠缠光场的纠缠程度以及双原子间偶极作用强度的影响很微弱.     

Bell态原子与双模纠缠相干光场相互作用的纠缠特性

运用Negativity熵研究了Bell态原子与双模纠缠相干光场相互作用系统中两个全同二能级原子之间的纠缠演化特性.分析了光场强度、光场纠缠度及原子间相互作用强度对纠缠的影响.结果表明:原子处于|β11〉时,两原子始终处于最大纠缠态;原子处于|β00〉时,初始纠缠的两原子始终较长时间处于退纠缠状态;原子处在|β10〉时,增大双模光场的平均光子数可以明显增大两原子之间的纠缠度并保持较大的纠缠状态;原子初态处在|β01〉时,原子间的相互作用强度对双原子间纠缠度有较显著的非线性调制作用.     

纠缠相干态光场驱动下∧-型三能级原子的辐射谱

采用时间演化算符方法,研究∧-型=三能级原子与纠缠相干态光场共振相互作用的辐射谱.给出了辐射谱一般公式,并讨论在纠缠相干态光场驱动下的辐射频谱结构.结果表明,无论下能级简并与否纠缠相干态光场平均光子数很小时均出现拉比分裂,且强度随双模光场纠缠程度的增加而增加.当两下能级简并时,若两模场的平均光子数较小,辐射谱呈现对称多峰结构,若两模场的平均光子数较大,辐射谱呈现对称五峰结构.当两下能级非简并时,若两模场的平均光子数较小,辐射谱呈现对称多峰结构.若两模场的平均光子数较大,辐射谱呈现对称十峰结构.纠缠相干光与非纠缠相干光辐射谱的本质差别有两点:一是双模光场强量子关联导致纠缠度越强拉比峰强度越高;二是存在纠缠时由于两模场相干性导致辐射谱呈现对称多峰结构.     

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.