利用非平衡光纤Mach-Zehnder干涉仪探测频率非简并纠缠态光场

采用两对光纤构成的非平衡Mach-Zehnder干涉仪,对非简并光学参量振荡腔产生的20mW频率非简并孪生光束间的强度差与位相和的关联噪声进行测量,在分析频率为2MHz处测得关联噪声分别低于散粒噪声基准31和13dB,从实验上证实了在较低分析频率处孪生光束之间有较高量子纠缠. 关键词： 光学参量振荡腔 孪生光束 光纤Mach-Zehnder干涉仪     

高功率孪生光束的产生与测量

讨论了一种用于运行于阈值以上的光学参量振荡器所产生的高功率孪生光束的测量方案。理论上讨论了分束器在高功率强度噪声测量中的作用,证明了分束器的引入并不影响强度量子关联的测量。并在实验上给出了高功率孪生光束的测量结果。     

正交振幅正关联正交位相反关联光束的贝尔态直接测量

提出了一种新的EPR光束关联度直接测量的方法.这种方法可以不用本地光直接测量具有正交振幅正关联、正交位相反关联特性的EPR光束的关联度.然后提出了在这种测量方法基础之上的量子密集编码实验方案.     

基于四波混频过程产生介于锥形探针光和锥形共轭光之间的多模量子关联

多模量子关联与纠缠在基础科学研究以及量子信息处理、量子通信等领域有着重要作用.本文基于热铷原子系综中的四波混频过程,通过构建具有空间结构的锥形泵浦光和锥形探针光,在实验上产生具有量子关联的锥形探针光和锥形共轭光,并测量到量子关联光束之间的强度差压缩约–2.6dB.通过改变单光子失谐、双光子失谐、泵浦光功率和铷原子池温度等实验参数,研究量子关联光束之间的强度差噪声随实验参数的变化关系.除此之外,通过“整体衰减法”和“局部切割法”对量子关联光束进行不同方式的处理,不仅实验测量了量子关联随透射率的变化关系,而且深入研究了量子关联的多模特性.本文的实验结果在量子信息处理以及量子通信领域有着潜在的应用价值.     

实用化多功能光压缩器

激光二极管抽运的YAPKTP内腔倍频单频激光器及其抽运的半整块非简并光学参量振荡腔(NOPO)被固定在一体的殷钢底座上构成了全固化多功能光压缩器———Squeezer.通过控制不同的工作条件,在此装置上可以产生多种类型压缩光:阈值以上产生约6dB(74%)量子相关孪生光束;在阈值以下,通过注入信号光参量缩小过程产生21dB明亮正交振幅压缩光;将参量放大器出射的两个频率简并偏振垂直的孪生光束分开,获得振幅反关联位相正关联明亮EPR源. 关键词： 光压缩器 光学参量振荡腔(OPO) 全固化     

利用孪生光束产生可调谐亚泊松光场

利用非简并光学参量振荡器（NOPO）产生的强度量子关联孪生光束，在实验上实现了波长可调谐的亚泊松光。实验获得最好亚泊松光噪声低于散粒噪声极限2．6dB；在7．4nm的波长调谐范围内，亚泊松光噪声低于散粒噪声2dB。同时，在实验上直接测量了亚泊松光的统计分布。     

非均匀关联随机电磁光束的产生

从理论和实验两方面对非均匀关联随机电磁光束的产生进行了研究.在理论出棊于相位关联与柑干度的联系推导出非均匀关联随机电磁光束的2×2交叉谱密度矩阵及相干性分布.理论分析表明,这种非均匀关联随机电磁光束中两点间的相干度不仅和两点间距有关,而且和两点的位置有关.在实验上,利用两个相位型液晶空间光调制器对入射的完全相干光的两个偏振分量分别加载随机相位调制,并测量了随机电磁光束的相干度分布.实验结果表明,光束中间距相等的两点之间的柑干度随着两点与光斑中心的距离的增加而减小.实验结果与理论结果一致.这种非均匀关联的随机电磁光束在自由空间光通信和激光微操控等领域具有广阔的应用前景.     

非均匀关联径向偏振部分相干光的产生

从理论和实验两方面对非均匀关联径向偏振部分相干光的产生进行了研究.理论上,基于相位关联与相干度的联系,推导出了非均匀关联径向偏振部分相干光的2×2阶交叉谱密度矩阵及相干度分布.实验上,利用一个相位型液晶空间光调制器的不同区域,对入射的完全相干的径向偏振光的两个正交偏振分量分别加载随机相位调制,并实验测量了这种光束的相干度分布及其对光强分布的影响.实验结果验证了光束相干度的非均匀关联结构,并且通过改变随机相位的高斯调制半宽可以改变光束的相干性分布.研究表明,随着随机相位的高斯调制半宽的增加,光束中两点间的相干度逐渐减小,其光强分布由圆环状逐渐变化为类平顶的光强分布.这种非均匀关联的径向偏振部分相干光在激光微操纵和材料加工等领域具有一定的潜在应用价值.     

用变分法研究超短超强脉冲在介质中的成丝

利用变分法将非线性薛定谔方程在形式上简化,把光束成丝等价于粒子在势阱中的运动,直观反映了自聚焦、衍射和多光子电离等机制对光束成丝的影响.实验得到了不同入射功率、光束口径、波面曲率半径等初始条件下脉冲在空气介质中的成丝过程和时间波形变化.通过半解析方法得到的结论能够定性解释成丝和多次聚焦现象等实验结果.     

涡旋光束的产生与干涉

分别从理论上和实验上研究了涡旋光束的产生和干涉现象.理论上分析了分数阶和整数阶涡旋光束同球面波以及平面波的干涉情况,并从实验上得出了其干涉图形.实验结果和理论模拟基本上一致.研究表明,随着涡旋光束拓扑荷数的变化,干涉图形也会产生变化.这一现象可用于测定分数阶涡旋光束的拓扑荷数.     

Realization of quantum correlation transfer between twin beams by conditional preparation technique

A conditional quantum correlation transfer is demonstrated experimentally for continuous variables by employing two pairs of twin-beams states. In present paper, the quantum correlation of twin beams is indicated by loss coefficient or “gemellity”, which is the remaining noise on the intensity difference normalized to the shot noise level. The quantum correlation between two initial idler beams with loss coefficient of 0.4 was conditionally transferred from two pairs of initially independent twin beams with loss coefficient of 0.2. A theory of conditional quantum correlation transfer and comparison between experimental results and theoretical prediction are also presented. The experimental results agree with the theory well.     

Transfer of intensity quantum correlation with twin beams

We demonstrate experimentally a protocol of transferring nonclassical quantum properties using two pairs of quantum-correlated twin beams in the continuous variable regime. The intensity quantum correlation from one twin beam is transferred to two initially independent idler beams with the help of a displacement transformation. It makes two originally independent beams exhibit an intensity quantum correlation of 0.8 dB below shot-noise level.     

Theoretical analysis of Raman scattering induced by a twin photon beam with quantum correlation

A Raman transition induced by a twin photon beam with quantum correlation, which is generated by nondegenerate parametric down-conversion, is theoretically analysed. The signal intensity of induced Raman scattering for the twin photon beam is twice as large as that for two coherent beams without correlation. Application of the twin photon beam is proposed for optical measurements of ESR spectra, which are useful for investigation of dislocations in semiconductor materials.     

在热压缩态中测量相位算符的涨落

利用热场动力学的方法计算了热压缩态中测量相位算符的涨落，引入了两种类型的基础量子涨落，一种是与测量相位的两个正交分量相联系，另一种是与一个测量相位分量和光子数相联系。由此，研究了热压缩压中测量相位涨落的两种压缩及其与温度的关系。     

Time-modulated entangled states of light

We investigate time-modulated EPR entangled states and intensity quantum correlation of twin light beams in application to time-resolved quantum communication. As a proper device generating such states, the nondegenerate optical parametric oscillator driven by the time-modulated pump field is considered. The text was submitted by the authors in English.     

Experimental characterization of quantum-correlated twin beams and a quantum channel with twin beams

We report the generation and characterization of quantum-correlated twin beams and their application to a quantum channel. Compared with our previous results, the characterization of twin beams and the quantum channel have been studied with 7.0-dB intensity difference squeezing. The measured inference variance of twin beams is decreased to 0.40 ± 0.02. For the quantum channel, the bit error rate will be 0.035 by using 7.0-dB intensity difference squeezing compared with our previous result of 0.067 by using 4.9-dB intensity difference squeezing.     

Generation of non classical states of light by phase conjugation and parametric conversion

It is shown that oscillators using nearly degenerate parametric conversion or four-wave mixing in the phase conjugation geometry generate pairs of highly correlated photons. The intensity difference of the two corresponding light beams is then expected to be below the shot noise limit. This property can be used to produce intensity stabilized light beams below the quantum limit. The phases of the twin beams also exhibit interesting correlation properties which will be discussed. Moreover, the combination of the twin beams gives a squeezed state, which has been observed by other authors when the device is below the oscillation threshold. We will describe preliminary results of experiments performedabove oscillation threshold.     

Continuous-wave quantum nondemolition measurements with vacuum and nonclassical meter input

QND measurements of the amplitude quadrature of continuous-wave light are performed with a monolithic dual-port degenerate optical parametric amplifier (OPA). Operated with a vacuum meter input, both output beams are squeezed and 33% correlated, demonstrating individually squeezed twin beams. The sum of the signal and meter transfer coefficients is 1.05, demonstrating operation as a quantum optical tap. The device exhibits quantum state preparation ability for both signal and meter output, reaching the conditional variances of dB and dB, respectively. An improved quantum measurement is realized by injecting 3.4 dB amplitude-squeezed light into the meter input port of the OPA. This achieves increased correlation and squeezing of the output beams, and both improved operation as a quantum optical tap and as a quantum state preparator. The all-solid-state system was operated for up to 5 hours with high stability. Received: 25 July 1996