Universal measurement of quantum correlations of radiation

A measurement technique is proposed which, in principle, allows one to observe the general space-time correlation properties of a quantized radiation field. Our method, called balanced homodyne correlation measurement, unifies the advantages of balanced homodyne detection with those of homodyne correlation measurements.     

The use of balanced homodyne and squeezed states for detecting weak optical signals in a Michelson interferometer

The possibility of using squeezed states and balanced homodyne detection of optical signals in a Michelson interferometer is discussed. The present analysis describes photon statistics measurements effects related to quadrature balanced homodyne detection showing the advantage of using this scheme for detecting weak optical signals.     

Ultrasensitive pulsed, balanced homodyne detector: application to time-domain quantum measurements

A pulsed, balanced homodyne detector has been developed for precise measurement of the electric field quadratures of pulsed optical quantum states. A high level of common mode suppression (>85 dB) and low electronic noise (730 electrons per pulse) provide a signal-to-noise ratio of 14 dB for measurement of the quantum noise of individual pulses. Measurements at repetition rates as high as 1 MHz are possible. As a test, quantum tomography of the coherent state was performed, and the Wigner function and the density matrix were reconstructed with 99.5% fidelity. The detection system can be used for ultrarsensitive balanced detection in cw mode, e.g., for weak absorption measurements.     

平衡零拍探测器的改进

平衡零拍探测技术是连续变量量子信息科学研究中测量量子态量子噪声的最佳方法之一。在平衡零拍探测系统中,需要一对性能和结构尽量相同的光电探测器,以便很好地减去经典噪声,有效探测散粒噪声基准及光场噪声。根据基尔霍夫电流定律及光电二极管串联的办法,设计并制作出一种性能优良的低噪声平衡零拍探测器。该探测器从光电二极管串联节点处取出光电流相减信号,然后对信号进行放大,在对两探测器全同性要求降低的同时提高了平衡零拍探测的性能。实验结果表明,该探测器在2MHz处共模抑制比达39dB,能很好地满足量子信息对低噪声、线性增益及高共模抑制比的要求。     

平衡零拍测量对连续变量量子密钥分配的影响

与单光子量子密钥分配采用单光子探测器不同，连续变量量子密钥分配采用平衡零拍测量技术.分析了由于参考光的真空噪声、分束器的透射率和反射率不相等引入的平衡零拍测量误差，以及平衡零拍测量探测器的电子噪声对连续变量量子密钥传输的最大安全距离的限制，给出了平衡零拍测量的探测噪声、电子噪声和密钥量之间的定量表达式.     

弱脉冲光时域平衡零拍测量的实验研究

设计了一套可以用来测量弱脉冲光时域噪声信息的平衡零拍探测系统,通过对本底光散粒噪声基准的测量分析了该系统的各项性能指标,并且对弱相干光脉冲进行了正交位相振幅分量的噪声测量。     

压缩态光场平衡零拍探测的位相锁定

平衡零拍探测是测量量子光场的重要方法之一. 通过对相位灵敏光学参量放大器注入的信号进行位相调制, 然后利用平衡零拍探测系统测量光学参量放大器输出的压缩光. 将相位灵敏光学参量分别运转在参量放大和参量缩小, 通过观察噪声谱中的调制信号就可确定测量的量子光场是正交振幅或位相分量. 通过解调位相调制信号可获得误差信号, 实现锁定平衡零拍探测系统本底光与待测光场相对位相为零(对应于待测光场振幅噪声分量). 关键词： 平衡零拍探测 位相锁定     

Characterization of ultrashort optical pulse properties by amplitude-modulation-balanced heterodyne gating

We present a general approach for the measurement of the properties of optical pulses by exploiting features of the optical carrier domain. We demonstrate the principle of a novel balanced detection scheme that avoids the difficulties associated with homodyne detection in the baseband used in linear optical sampling methods so far. The residual timing instability of the repetition rate synchronization between mode-locked lasers is measured with the new detection technique.     

实验条件不完美对薛定谔猫态制备的影响

薛定谔猫态是一类重要的非经典光场,实验上可以通过真空压缩态减光子的方案获得.本文从理论上研究了实验条件对制备薛定谔猫态的影响,主要考虑了包括压缩态的压缩度和纯度、单光子探测器的效率及噪声以及零拍探测器的效率等诸多因素的影响.理想情况下通过减光子方案制备得到的薛定谔猫态为奇光子数态,其相空间原点的Wigner函数为负值是其非经典特性的重要判据,而保真度可以度量制备态与理想猫态之间的相似程度.在压缩态为非纯态以及单光子探测器为商用低效率阈值探测器的情况下,计算了制备猫态的保真度、Wigner函数及其相空间原点处W（0）的表达式,分析了实验条件对薛定谔猫态制备的影响,为制备高质量的薛定谔猫态提供了理论指导.     

HOW DOES AN IMPERFECT SYSTEM AFFECT THE MEASUREMENT OF SQUEEZING?

The effect of an imperfect system on the measurement of squeezing is studied. It is shown that the imperfectly efficient detectors and the unbalance of the beam-splitter will reduce the measured squeezing. The effects on quadrat ure phase squeezing and photon number squeezing are different from the usual balanced homodyne detection.     

低频压缩态光场的制备

低频压缩态光场可用于提高引力波探测器灵敏度, 近年来受到人们的广泛关注. 相对于高频段而言, 低频压缩态的产生更容易受到外界环境噪声的干扰而不易被观察到. 本文采用全固化单频倍频Nd: YVO4/KTP激光器作为光源, 利用双波长共振的光学参量振荡器实现参量过程, 以1064 nm波长的红外作为基频光, 激光器腔内倍频产生的532 nm绿光作为抽运光, 通过调节周期性极化磷酸氧钛钾晶体温度使光学参量振荡器达到双波长同时共振, 采用真空注入的方式, 利用Pound-Drever-Hall锁腔技术锁定抽运场. 输出压缩光通过平衡零拍探测, 最终在实验上获得了频率低至3 kHz的真空压缩, 所直接观察到的压缩度为2 dB.     

平衡零拍平移测量实验研究

利用平衡零拍探测方法对TEM00模相干光激光束的微小平移进行一维测量的实验研究,实验装置最小可测平移量为0.3nm.实验验证了平移与倾斜这两个物理量之间的共轭关系.最后用模式重叠的概念分析了本底光偏离标准的TEM10模对测量结果的影响.实验结果与理论基本符合.     

两种连续变量爱因斯坦波多尔斯基罗森关联测量方法的比较

讨论了测量连续变量爱因斯坦－波多尔斯基－罗森（EPR）关联的两种实验方法，由于在平衡零拍探测和贝尔态直接测量中为标定关联度所选取的参考基准不同，造成谱仪显示的结果有所差异，但经过基准变换，所测得的耦合模压缩度，爱因斯坦－波多尔斯基－罗森关联度以及它们之间的换算关系均一致。从理论上分析了测量原理，并从实验角度讨论了两种方法的优缺点。     

Continuous variable tomographic measurements

Using a recent result of Albini et al. [P. Albini, E. De Vito, A. Toigo, J. Phys. A: Math. Theor. 42 (2009) 295302] to represent quantum homodyne tomography in terms of a single observable (as a normalized positive operator measure) we construct a generalized Markov kernel which transforms the measurement outcome statistics of this observable into the measurement outcome statistics of a covariant phase space observable. We also consider the inverse question. Finally, we add some remarks on the quantum theoretical justification of the experimental implementations of these observables in terms of balanced homodyne and 8-port detection techniques, respectively.     

利用交叉克尔非线性产生四光子偏振态簇态

提出了一种基于交叉克尔非线性效应产生四光子偏振态簇态的方案,与其他产生四光子簇态的方案比较,该方案引入宇称门的思想和用到基于零差探测的非破坏测量方法,使得该方案在实验上更易于操作及实现.     

Distillation of squeezing from non-Gaussian quantum states

We show that single copy distillation of squeezing from continuous variable non-Gaussian states is possible using linear optics and conditional homodyne detection. A specific non-Gaussian noise source, corresponding to a random linear displacement, is investigated experimentally. Conditioning the signal on a tap measurement, we observe probabilistic recovery of squeezing.     

基于信道估计的自适应连续变量量子密钥分发方法

为使连续变量量子密钥分发协议获得稳定的密钥生成率,需要根据信道变化动态调整发送光脉冲的强度.将光纤量子信道看作加性玻色量子高斯信道,给出高斯态通过玻色量子高斯信道仍得到高斯态的证明过程.通过平衡零差检测后,采用最大似然估计法得到了信道参数,进而根据估计的噪声大小自适应调整Alice发送的光脉冲的强度,从而获得稳定的密钥生成率. 关键词： 量子密钥分发 连续变量 玻色量子高斯信道 信道估计     

Retrodiction for coherent communication with homodyne or heterodyne detection

Previous work on the retrodictive theory of direct detection is extended to cover the homodyne detection of coherent optical signal states and . The retrodictive input state probabilities are obtained by the application of Bayes' theorem to the corresponding predictive distributions, based on the probability operator measure (POM) elements for the homodyne process. Results are derived for the retrodictive information on the complex amplitude of the signal field obtainable from the difference photocount statistics of both 4-port and 8-port balanced homodyne detection schemes. The local oscillator is usually assumed much stronger than the signal but the case of equal strengths in 4-port detection is also considered. The calculated probability distributions and error rates are illustrated numerically for values of signal and local oscillator strengths that extend from the classical to the quantum regimes.     

Wigner function and tomogram of the excited squeezed vacuum state

The excited squeezed light (ESL) can be the outcome of interaction between squeezed light probe and excited atom, which can explore the status and the structure of the atom. We calculate the Wigner function and tomogram of ESL that may be comparable to the experimental measurement of quadrature-amplitude distribution for the light field obtained using balanced homodyne detection. The method of calculation seems new.