小样本光子图像的统计处理

讨论了一种对小样本光子图像的统计处理方法。在超微弱发光的研究中（例如细胞的超微弱荧光）,由于发光强度极弱,需要用像增强器对超微弱发光图像进行增强得到可视图像,超微弱发光图像不可避免地受到像增强系统暗噪声及背景噪声的影响,使光子图像湮没在噪声中。为从原始图像中检验出信号,根据信号光子和噪声光子的不同统计分布,运用信号检测与的方法判断光子是否属于信号光子,并得到一简明的判据,由此判据剔除图像中的噪声光子,得到信噪比改善的光子图像。并用此方法处理了人掌的超微弱发光光子图像。     

光子图像统计处理

讨论了一种对有限光子图像累加的统计处理方法。在超微弱发光的研究中（例如细胞的超微弱光），由于发光强度较弱，需要用像增强器对超微弱发光图像进行增强得到可视光子图像，超微弱发光的光子图像不可避免地受到像增强系统暗噪声及背景噪声的影响，使光子图像湮没在噪声中。为从原始图像中检验出信号，常将采集到的有限光子图像进行累加以增加样本数，根据信号光子和噪声光子的不同统计分布，运用似然比检验方法得到有效判断累加图像中某像素是否含有信号光子，由此剔除图像中的噪声光子，得到信噪比改善的光子图像。     

Exploring energy-time entanglement using geometric phase

Using the signal and idler photons produced by parametric down-conversion, we report an experimental observation of a violation of the Bell inequality for energy and time based purely on the geometric phases of the signal and idler photons. We thus show that energy-time entanglement between the signal and idler photons can be explored by means of their geometric phases. These results may have important practical implications for quantum information science by providing an additional means by which entanglement can be manipulated.     

Improving the spectral purity of single photons by a single-interferometer-coupled microring

We experimentally engineer a high-spectral-purity single-photon source using a single-interferometer-coupled silicon microring. By the reconfiguration of the interferometer, different coupling conditions can be obtained, corresponding to different quality factors for the pump and signal/idler. The ratio between the quality factor of the pump and signal/idler ranges from 0.29 to 2.57. By constructing the signal—idler joint spectral intensity, we intuitively demonstrate the spectral correlation of the signal and idler. As the ratio between the quality factor of the pump and signal/idler increases, the spectral correlation of the signal and idler decreases, i.e., the spectral purity of the signal/idler photons increases. Furthermore, time-integrated second-order correlation of the signal photons is measured, giving a value up to 94.95±3.46%. Such high-spectral-purity photons will improve the visibility of quantum interference and facilitate the development of on-chip quantum information processing.     

Two-order Interference of Single Photon

A pair of photons called signal and idler photons, respectively, are produced through the nonlinear process of type-I spontaneous parametric downconversion in BBO crystal pumped by the second-harmonic wave of a Ti:sapphire femtosecond laser pulse. The two-order interference phenomenon of the signal photon in Michelson interferometer is observed and give an analysis in detail.     

Generation of photon pairs in dispersion shift fibers through spontaneous four wave mixing: Influence of self-phase modulation

Correlated signal and idler photon pairs with small detuning in the telecom band can be generated through spontaneous four-wave mixing in dispersion shift fibers. However, photons originated from other nonlinear processes in optical fibers, such as Raman scattering and self-phase modulation, may contaminate the photon pairs. It has been proved that photons produced by Raman scattering are the background noise of photon pairs. Here we show that photons induced by self-phase modulation of pump pulses are another origin of background noise. After studying the dependence of self-phase modulation induced photons in signal and idler bands, we demonstrate that the quantum correlation of photon pairs can be degraded by the self-phase modulation effect. The investigations are useful for characterizing and optimizing an all fiber source of photon pairs.     

Optical-fiber source of polarization-entangled photons in the 1550 nm telecom band

We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.     

光学超晶格中级联参量过程制备纠缠光子对

探索制备纠缠光子对的新途径是量子光学领域的一个研究热点.从理论上证明在准周期极化 的光学超晶格晶体中的级联参量过程能够产生纠缠光子对.分别利用脉冲和连续的532nm抽运 光在一块准周期极化的 LiTaO3晶体中同时实现非简并参量下转换（产生信号光与闲置光 ）与和频（闲置光与抽运光和频生成和频光）的级联参量过程，获得630nm的信号光与460nm 的和频光.指出信号光与和频光之间存在纠缠关联性质.该方案的优点是可产生短波长的纠缠 光子对. 关键词： 准相位匹配 级联参量过程 光量子纠缠态     

The formation of a light field with suppressed photon fluctuations by nonlinear optical methods

A quantum theory is developed to describe optical parametric amplification under low-frequency pumping, which is observed in nonlinear photonic crystals in sequential interactions of light waves with multiple frequencies. Spatial variations of the mean number of photons and the Fano factor at signal and additional frequencies are analyzed. It is shown that a field with a sub-Poisson statistics of photons can be formed at a signal frequency which is 1.5 times higher than the frequency of pumping.     

Effects of multi-Schell beams on orbital angular momentum of entangled signal photons in low-order turbulence aberration channels

We model the detection and crosstalk probability of orbital angular momentum (OAM) states of the entangled signal photon in the Kolmogorov channels of the low-order turbulence aberrations and by the Rytov approximation. The results show that lower OAM mode number of signal photons and larger sub-beam number of multi-Gaussian Schell-model pump beam, the less susceptible of the detection probability of the signal photon to spatial coherence of source and turbulence aberrations is achieved. The maximum crosstalk probability is decrease as the decreasing of the sub-beam number of multi-Gaussian Schell-model. Enlarging OAM difference value or decreasing sub-beam number of multi-Gaussian Schell-model pump beam results in a lower crosstalk probability of the OAM of entangled signal photons.     

Stimulated emission as a result of multiphoton interference

By performing an experiment on stimulated emission by two photons in the parametric amplification process and comparing it to a three-photon interference scheme, we present evidence in support of the idea that the underlying physics of stimulated emission is simply the constructive interference due to photon indistinguishability. So the observed signal enhancement upon the input of photons can be interpreted as a result of multiphoton interference of the input photons and the otherwise spontaneously emitted photon from the amplifier.     

All-optical switching at ultralow light levels

We report an experimental demonstration of all-optical switching at ultralow light levels in coherently prepared Rb atoms. A signal light pulse is switched on and off by a control light pulse at different frequencies in a four-level atomic system based on multiphoton interferences. We observed a switching efficiency of 55% with the signal and control light pulses containing approximately 20 photons each, corresponding to a control energy density of approximately 10(-5) photons per atomic cross section lambda(2)/(2pi).     

Detection of VUV photons with large-area avalanche photodiodes

The room-temperature response of large-area avalanche photodiodes (LAAPDs) to 128- and 172-nm light pulses is investigated. The minimum detectable number of photons, which can produce a signal just above the noise level, is found to be around 1300 and 600 photons, respectively. The LAAPD relative statistical fluctuations in the detection of 15 000 photons of 128 nm and 25 500 photons of 172 nm were found to be about 3.9% and 2.2%, respectively. Both the minimum detectable number of photons and statistical fluctuations do not depend on the photon wavelength, but rather on the number of charge carriers produced by the light pulse in the LAAPD. For these light levels, good LAAPD performance is already achieved for gains as low as 30 to 60.     

Der optische parametrische Oszillator. II. Amplitudenfluktuationen der Strahlung bei durchlaufender Pumpwelle

Amplitude fluctuations of the signal wave of an optical parametric oscillator are evaluated for the case of nonresonant pumping by calculating the decrease of a random deviation ε of the signal amplitude from its stationary value during a round trip through the (ring) resonator. From this, a damping term governing the temporal behaviour of ε is deduced which, together with a Langevin force connected with the spontaneous decay of pump photons into both signal and idler photons, determines the amplitude fluctuations of the signal wave. In addition, it is shown that the same results may be obtained from a mode formalism for signal and idler waves taking into account the spatial variation of the pump wave following from Maxwell's equations.     

化学发光法大气氮氧化物浓度自动分析仪中光信号探测模块温控系统设计

化学发光法是测量低浓度的大气氮氧化物含量的有效方法,可用于24h连续自动分析的大气环境监测系统。然而该方法需要高温转换室、高压臭氧发生模块、高温反应室等模块,使得仪器内的环境分布极为复杂,仪器在长时间运行后容易出现灵敏度下降、信噪比降低等现象。针对上述现象,设计了用于仪器的光信号探测模块的温度控制系统。该温控系统基于PID控制原理,通过AVR单片机ATMEGAl6对半导体制冷片（Ther—mo—ElectricCooling,TEC）的闭环控制来实现温度的精密控制。实验结果表明,该系统可以使光信号探测模块的温度控制在5℃±0．1℃,光电倍增管的暗噪声从25℃时的363个／s下降到5℃时的8个／s光子数,噪声波动标准差也从22降到3,能够很好地满足系统对信号探测稳定性的要求。     

Fluktuationen beim optischen parametrischen Oszillator

In a heuristic manner – analogous to the procedure known from laser theory – the correlation functions for the fluctuation operators (Langevin forces) connected with the spontaneous decay of pump photons into both signal and idler photons as well as the loss mechanism for the radiation are calculated.     

一种生成质量最优路径纠缠微波信号的压缩参量选择方法

介绍了路径纠缠微波及其生成原理,将生成信号以量子力学算符的形式表示,并在光子数态表象下展开,定性地给出了生成信号与压缩参量之间的关系.提出了一种路径纠缠微波信号质量评价方法,即通过信号中纠缠微波光子总数的期望值表征信号的纠缠度,间接实现对信号质量的评价.基于这种信号质量评价方法,提出了一种生成质量最优路径纠缠微波信号的压缩参量选取方法:在近似确定有效纠缠微波光子数的前提下,找出生成不同微波光子数纠缠概率最大时的一组压缩参量值,进而得出各个压缩参量值所对应的一组纠缠微波光子总数的期望值,其中的最大值对应的压缩参量值即为生成质量最优信号所要选择的压缩参量值.通过理论分析,发现路径纠缠微波信号质量由压缩参量决定,且只与压缩幅有关,而与压缩角无关.仿真实验结果表明,在纠缠微波光子数的最大有效值取为"26"时,纠缠微波光子总数期望值的最大值对应的压缩幅值为1.77,即压缩幅取此值时所得到的路径纠缠微波信号质量最佳,仿真结果表明该方法是有效的.本文的研究为路径纠缠微波在实验研究和实际应用中如何生成高质量信号的问题提供了思路.     

光子成像静止点目标的管道滤波探测方法

构建了具有单光子成像能力的光子成像系统,提出应用管道滤波方法实现对光子受限静止点目标的探测。分析了光子图像静止点目标与点状噪声特征,根据静止点目标在序列图像中位置的确定性以及噪声点的不相关性,研究了基于管道滤波的光子成像静止点目标探测方法。为降低目标探测的虚警概率,优化了管道滤波直径。以实验采集得到的多组光子图像序列为样本,获得了探测概率、虚警概率与信号光子数、噪声光子数、管道长度以及检测阈值的关系。检测结果显示,对信号与噪声的平均发生率为0.4和5.215的序列图像,当管道长度为9、检测阈值为2时,探测概率达0.9以上且虚警概率〈0.08。对比多组图像序列的检测结果表明,影响探测概率的主要参数是信号光子数,而影响虚警概率的主要参数是噪声光子数。     

PRODUCTION OF LARGE-TRANSVERSE-MOMENTUM PHOTONS AND THE QCD PHASE TRANSITION IN ULTRARELATIVISTIC NUCLEAR COLLISIONS

The production of large-transverse-momentum photons from Quark-Gluon Plasma (QGP) is discussed,and is used to analyze the high multiplicity event found in the Japanese-American Cooperative Emulsion Experiment (JACCEE).The theoretical result turns out to fit the experiment well.Thus the production of large transverse momentum photons provides an experimental signal of the QCD phase transition.     

激光器型全光波长转换器的小信号分析

当外部光子注入到激光器有源腔中时 ,载流子把被注入光子消耗的一部分放大 ,进而激光器自身的输出功率将降低。基于此 ,可以实现全光波长转换。理论上基于载流子消耗机制 ,对激光器型波长转换器进行了小信号分析 ,给出了频率响应函数。理论分析表明 ,激光器型全光波长转换器的转换速度取决于激光器光子寿命以及激光器腔内的光子密度。