耦合腔场中原子共生纠缠对的研究

研究了耦合腔场模型下原子纠缠与光腔场纠缠的演化与转移问题.发现在不同Bell型初态下,光腔场间耦合参数对初始纠缠的演化行为起到了不同的作用.对第一类Bell态cosθ| e,e〉+sinθ| g,g〉,调节腔场间耦合参数既可以起到延长原子纠缠死亡时间的作用,又可以起到保护初始原子纠缠的效果.而对第二类Bell态cosθ| e,g〉+sinθ| g,e〉,腔场耦合参数对原子间初始纠缠只起到保护作用.     

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.     

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.     

原子与腔场耗散系统中的线性熵演化

研究了两个全同二能级原子同时与单模耗散腔场发生大失谐相互作用时，原子-场系统、两原子子系统的线性熵演化，以及原子的初始状态与腔的耗散因素对各线性熵的影响.研究结果表明:腔场的衰变常数对不同类型的Bell纠缠态的影响完全不同，其中|Ψ〉₁₂态具有强烈的抗消纠缠的能力，而|Φ〉₁₂态是一个脆弱的纠缠态. 关键词： 腔耗散 原子纠缠 纠缠退化 线性熵     

双模纠缠相干光场与Bell态原子相互作用系统的光场压缩效应

运用求解Schrdinger方程和数值计算方法,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场压缩特性,分析了双模纠缠相干光场的纠缠程度、双模纠缠相干光场的初始平均光子数对光场压缩性质的影响,以及两纠缠原子的相互作用强度对光场压缩性质的影响.结果表明:若初始时刻原子处在Bell态|β11〉,则不出现光场的压缩效应,而处在另外三种Bell态时,在一定的条件下均可呈现光场的压缩效应.光场压缩效应不仅与初始光场的平均光子数以及原子的初态有关而且与双模纠缠相干光场的纠缠程度有关,但与两纠缠原子的相互作用强度的大小没有明显的关系.     

开放系统中量子比特与环境纠缠特性的研究

研究了由两个二能级原子与一个零温热库所组成的系统的纠缠动力学过程.考虑原子间的偶偶相互作用及原子与热库之间的失谐,对于初始原子间有纠缠与无纠缠两种情况,研究了不同的参数条件对系统纠缠的影响.计算了两原子间、原子与热库之间的对纠缠以及整个系统的三体纠缠,结果表明在两原子初始处于最大纠缠态时,所有的对纠缠最终都趋于零.增大原子间的偶偶相互作用强度,原子与热库之间的纠缠会被减弱,而原子间的纠缠以及系统三体间的纠缠被增强.增大原子与热库之间的失谐量,两原子之间的纠缠会增大,原子与热库以及三体间的纠缠会减弱.     

Bell态原子与双模纠缠相干光场双光子相互作用的原子布居数演化特性

运用全量子理论研究了Bell态原子与双模纠缠相干光场双光子相互作用过程中的原子粒子布居差的时间演化规律.结果表明:原子初始处于|β11＞时,原子粒子布居差恒为零;原子初始处于其他三个Bell态时,随着初始光场平均光子数的增加,原子粒子数布居差时间演化曲线的振荡频率明显增大,振荡幅度明显减小;双模光场纠缠程度的大小对曲线的振荡频率及整体曲线的位置都没有影响.随着原子间偶极相互作用的增强,当原子初态处在|β01＞时,曲线的Rabi振荡频率明显增大;而两原子初始处于|β10＞或|β00＞态时,曲线的崩塌-回复现象逐渐消失.     

噪声环境中两粒子纠缠态的纠缠消相干

借助于共生纠缠度和输入输出保真度考察了初始处于纠缠态的两粒子在联合噪声环境中的消纠缠特性.结果表明:两粒子纠缠态可分为相干保持态和脆弱纠缠态.对于脆弱纠缠态分析了它们在低温条件欧姆型耗散下的纠缠消相干演化动力学. 关键词： 热库 相干保持态 脆弱纠缠态 输入输出保真度     

与两等同Bell态纠缠原子相互作用光场的量子场熵

利用全量子理论,并通过数值计算,研究了初始处于Fock态的单模光场与两等同双能级纠缠原子单光子共振相互作用过程中单模光场量子场熵的时间演化特性.结果发现:当两原子初始处于第一种Bell态时,光场量子场熵的时间演化周期为π/g2(2n+1);随着初始光强的增大,光场与原子之间的量子纠缠现象减弱;特别是当时间t为演化周期的整数倍时,场－原子系统处于退纠缠状态.当两原子初始处于第二种Bell态时,光场量子场熵不随时间变化,恒为零.当两原子初始分别处于第三种和第四种Bell态时,光场量子场熵的时间演化曲线呈现不等幅周期振荡现象;并且随着初始光场光子数的增加,光场量子场熵的振荡周期逐渐增大,但振荡幅值逐渐减小.     

热辐射场中两个耦合的二能级原子量子态的纠缠(英文)

两个偶极耦合的二能级原子置于热辐射场中,原子用泡利算符描述,环境用无穷的谐振子热库描述,运用密度矩阵方法,得到两能级原子密度矩阵元演化规律.针对三种不同的初始状态,利用共生纠缠度分析置于热辐射场中原子量子态的纠缠.结果表明:当两个原子初始处于不同量子叠加态时,原子的纠缠呈现出明显的差异.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.