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.     

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.     

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     

孪生光束时域内的关联特性

本文在实验上测量了运转于阈值以上的双共振光学参量振荡器所产生的孪生光束在时域内的关联特性.在分析腔带宽对孪生光束强度量子关联影响的基础上,通过时域内的数据采集,运用改变孪生光束其中一臂的时间延时的方法来考察时域内孪生光束关联度的变化.在实验上给出了孪生光束关联度大小随时间变化的结果.     

Conditional preparation of a quantum state in the continuous variable regime: generation of a sub-Poissonian state from twin beams

We report the first experimental demonstration of conditional preparation of a nonclassical state of light in the continuous variable regime. Starting from a nondegenerate optical parametric oscillator which generates above threshold quantum intensity correlated signal and idler "twin beams," we keep the recorded values of the signal intensity only when the idler intensity falls inside a band narrower than its standard deviation. By this very simple technique, we generate a sub-Poissonian state 4.4 dB (64%) below shot noise from twin beams exhibiting 7.5 dB (82%) of noise reduction in the intensity difference.     

Absolute detector calibration using twin beams

A method for the determination of absolute quantum detection efficiency is suggested based on the measurement of photocount statistics of twin beams. The measured histograms of joint signal-idler photocount statistics allow us to eliminate an additional noise superimposed on an ideal calibration field composed of only photon pairs. This makes the method superior above other approaches presently used. Twin beams are described using a paired variant of quantum superposition of signal and noise.     

利用光子相关性降低量子噪声

本文分析了双光路强度差测量的量子理论,指出可以利用两光束之间的光子相关性来降低强度差测量的量子噪声〈Δ?_d²〉,对于具有强相关性的违反Cauchy-Schwarz不等式的光场(简称ACS非经典光场)〈Δ?_d²〉可低于经典噪声极限,这种情况可发生在简并四波混频(DFWM)的共轭波和透射波之间。 关键词：     

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     

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。     

Theory for quantum state of photon pairs generated from spontaneous parametric down-conversion nonlinear process

A theory is presented for the quantum state of photon pairs generated from spontaneous parametric down-conversion nonlinear process. In this theory, the influence of the final sizes of nonlinear optical crystals on optical eigenmodes is explicitly taken into consideration. It was found that these photon pairs are not in entangled quantum states. Polarization correlations between the signal beam and the idler beam are explained. It is also shown that the two photons generated from SPDC are not spatially separated, therefore the polarization correlation between the signal and idler beams is not an evidence for quantum non-locality. The text was submitted by the authors in English.     

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。     

Sub-shot-noise heterodyne polarimetry

We report an experimental demonstration of a heterodyne polarization rotation measurement with a noise floor 4.8 dB below the optical shot noise by use of classically phase-locked quantum twin beams emitted above threshold by an ultrastable type II Na:KTP cw optical parametric oscillator. We believe that this is the largest noise reduction achieved to date in optical phase-difference measurements.     

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.     

Generation and application of twin beams from an optical parametric oscillator including an alpha-cut KTP crystal

Measurement slight amounts of absorption of light with accuracy beyond the standard quantum limit has been experimentally demonstrated. The quantum-correlated twin beams used in the measurement were generated from a nondegenerate optical parametric oscillator including an alpha-cut KTiOPO(4) crystal pumped by an intracavity frequency-doubled Nd:YAG laser. The noise in the intensity difference between the twin beams was reduced by 88% below the standard quantum limit (SQL). The signal-to-noise ratio was improved by 7 dB with respect to the SQL of the total light employed in the experiment and by 4 dB with respect to that of the signal light.     

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.     

Investigation of the influence of extra noises in seed beams on continuous-variable entanglement generation

The influence of the extra classical noises in seed beams on the entanglement between the signal and the idler modes of the output fields generated by a non-degenerate optical parametric amplifier operating at deamplification is investigated theoretically and experimentally.With the increase of the extra classical noises in the seed beams,the correlation degree of the output entangled optical fields,which is scaled by the quantum noise limit,decreases rapidly.The experimental results are in good agreement with the theoretical calculations.     

Quantum interference of multimode two-photon pairs with a Michelson interferometer

We perform the second-order quantum interference experiment with the multimode photon pairs produced via an optical parametric oscillator far below threshold in a Michelson interferometer, measure the second-order correlation function in different cases. We find when the interferometer is highly unbalanced, the shape of the second-order correlation function is clearly dependent on the path length difference between two interfering beams. On the contrary, when the interferometer is nearly balanced, beside its height, the shape of the second-order correlation function is independent on the small path length difference. The second-order correlation function shows a multipeaked structure in both cases. All experimental results agree very well with the theoretical predictions.     

单模激光系统线性化近似适用范围的分析

采用线性化近似方法计算了具有实虚部关联的量子噪声和泵噪声驱动的单模激光损失模型的光强相对涨落,为了对线性化近似的适用范围进行详细的分析,分别讨论了量子噪声强度、泵噪声强度、量子噪声实虚部间关联系数对光强相对涨落的影响,得出在小噪声、远离阈值时,线性化近似适用范围扩大;小噪声、远离阈值且当量子噪声实虚部无关联时,线性化近似适用范围极大的结论.     

Coincidence Imaging and interference with coherent Gaussian beams

we present a theoretical study of coincidence imaging and interference with coherent Gaussian beams. The equations for the coincidence image formation and interference fringes are derived, from which it is clear that the imaging is due to the corresponding focusing in the two paths. The quality and visibility of the images and fringes can be high simultaneously. The nature of the coincidence imaging and interference between quantum entangled photon pairs and coherent Gaussian beams are different. The coincidence image with coherent Gaussian beams is due to intensity-intensity correspondence, a classical nature, while that with entangled photon pairs is due to the amplitude correlation a quantum nature. Selected from Acta Sinica Quantum Optica, 2005, 11(4)(in Chinese)     

相干高斯光束的符合成像和干涉

理论上研究分析了相干高斯光束的符合成像和干涉.导出了相干高斯光束的符合成像公式和符合干涉条纹公式,从这些公式可以看出符合成像和干涉是由于两条光路相应的汇聚投射引起的.符合成像和干涉条纹的质量及能见度可以同时很好.我们的结果表明纠缠光子对和相干高斯光束的符合成像及干涉的物理本质是不同的,相干高斯光束的符合成像和干涉的物理本质是光强的点对点投射,而纠缠光子对的符合成像和干涉的物理本质是双光子的振幅关联.