压缩真空态与压缩单光子态的相干叠加态的非经典性质

通过对量子比特态进行压缩操作,获得压缩真空态与压缩单光子态按一定的权重比例叠加而成的相干叠加态,此相干叠加态与压缩参数和权重因子有关,研究其非经典性和非高斯性.研究结果表明,通过压缩使得量子比特态的光子数分布范围变宽了.特别是从亚泊松分布和Wigner函数负定性情况分析了该量子态的非经典属性,从Wigner函数的边缘分布角度观察了该量子态的非高斯性.发现调节权重因子和压缩参数可以改善该态的非经典性和非高斯性.     

拉盖尔多项式算符激发相干态的非经典性质

将拉盖尔多项式算符作用在相干态上,构造了拉盖尔多项式算符激发相干态.利用有序算符积分技术,导出了它的归一化系数以及〈a^la^+m〉的计算表达式.采用数值计算方法,讨论了相干态相位角和平均光子数对它的非经典性质的影响.研究结果表明:一阶拉盖尔多项式算符激发相干态呈现出压缩效应、反聚束效应、亚泊松分布和Wigner函数负性等量子特性,并且相干态的相位角对它的量子特性有重要影响;另一方面,随相干态平均光子数增大,它的反聚束效应和亚泊松分布性质逐渐减弱,压缩效应和Wigner函数的负性却先增强,而后又逐渐减弱.     

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.     

非线性圆态及其非经典性质

为了研究非线性和叠加效应对量子态的影响,采用理论分析和数值计算相结合的方法,研究了一种新的量子态,即非线性圆态。分析了该态的平均光子数分布、亚泊松分布、压缩效应等非经典性质,同时计算了它的维格纳(Wigner)函数。数值模拟结果表明:随着Lamb-Dicke参数和叠加态数目的增大,非线性圆态的平均光子数增加,而由该态描述的光场的亚泊松分布和压缩效应受到减弱。表征非线性效应的Lamb-Dicke参数和叠加态数目对该态的非经典特性有明显的影响。     

光场组合算符激发混沌场的量子特性

利用算符作用在光场态上构造新的量子态的方法,通过光场湮没和产生算符的线性组合作用构造了光场组合算符激发混沌场。通过对光场的两个正交分量涨落、二阶关联函数、Mandel Q参量和Wigner函数的计算,研究了该量子态的压缩效应、反聚束效应、统计性质和Wigner函数的负性。讨论了算符叠加系数变化和平均光子数变化对其量子特性的影响。研究结果表明:光场不呈现压缩效应;随平均光子数增大它的反聚束效应、亚泊松分布性质和Wigner函数负性减弱;另一方面,随算符组合部分中产生算符的比重增大,光场反聚束效应和亚泊松分布性质增强。这表明增大算符组合部分中产生算符的比重对增强光场反聚束效应和亚泊松分布性质有利。     

相空间中相互垂直的相干态迭加态以及相应的双模纠缠态研究

相干态是最接近经典态的量子态，而广泛研究的相干迭加态——如奇偶相干态、Schleich的镜像迭加相干态等——则显示更多非经典效应。另外，双模及多模迭加态，特别是所谓的纠缠态，在量子信息处理如量子隐形传态和量子密码术中扮演重要角色。我们就相空间中相互垂直的相干态的迭加态进行讨论，研究其非经典特性，如光子数统计分布、正交分量压缩效应、Wigner分布函数的负性以及由此引入的非经典判别子。结果表明，这一类相干迭加态在满足某种条件下具有亚泊松光子统计分布和正交分量的压缩效应，并且参数变量在一定范围内这两种非经典效应同时存在；这些迭加态的Wigner分布中存在不同程度的负值区域．并与奇偶相干态做出了比较．计算相廊的Wigner函数积分判别子可以定最地分析其负性的深度。     

增光子圆态及其性质

利用光场产生算符的逆算符作用于圆态来构造增光子圆态.讨论了此态的非经典性质,同时计算并模拟出它的维格纳(Wigner)函数.结果表明,在不同光强下,随着激发数的增大增光子圆态光场的平均光子数增加与减少交替地出现;光子激发后,光场的亚泊松统计特性得到增强,压缩效应却受到抑制.维格纳函数图像显示了增光子圆态显著的非经典性质,发现了光子激发与圆态光强的增大都能使量子态由叠加引起的干涉效应明显增强.另外,在不同叠加数的情况下,通过适当选择参量可使维格纳函数具有相同的变化规律.     

光子扣除(增加)压缩真空态与压缩猫态的保真度

解析推导了任意光子扣除(增加)压缩真空态与压缩猫态的保真度. 研究表明,无论是光子增加还是光子扣除,最大保真度都随光子增加或扣除数目的增加而增加,且最大保真度对应的叠加态振幅也增加;此外,对于相同数目的增加和扣除光子数,光子增加后的最大保真度所对应的叠加态振幅比光子扣除所对应的叠加态振幅要大,而最大保真度略小一些. 尽管目前从实验上实现光子增加比光子扣除困难较大,但光子增加也可以成为获得大振幅猫态的一个有力手段. 关键词： 光子扣除压缩真空态 光子增加压缩真空态 压缩猫态 保真度     

平移激发压缩真空态及其性质

引入平移激发压缩真空态D(z)a\+\{+m\}S(r)|0〉,并讨论它的一些基本性质.利用正规 乘积内的积分技术,证明了其完备性.平移激发以后,与压缩真空态相比较,光子数分布 的振荡性质更加显著.与压缩真空态的光子总是聚束的性质不同,在平移参量|z|和激发 数m都较小时,平移激发压缩真空态的光子统计关联可以呈现反聚束效应.计算了它的准 概率分布函数(Q函数和Wigner函数),并讨论了它们对各参量的依赖关系,从Wigner函数可 以清楚地看出该量子态的非经典特性. 关键词：     

增加光子纠缠相干态的统计性质

引入了增加光子纠缠相干态.研究了在纠缠相干态的某个模上加入光子对光场统计性质的影响.由于两个场模间的纠缠,在a模上加入光子不但可以使a模的平均光子数增加,也可以使b模的平均光子数发生变化(增加或减少).加入光子后,光场的亚泊松分布和压缩特征得到明显增强. 关键词： 纠缠 增加光子态 统计性质     

Simultaneous Preparation of Two Optical Cat States Based on a Nondegenerate Optical Parametric Amplifier

The cat state, known as the superposition of coherent states, has broad applications in quantum computation and quantum metrology. Increasing the number of optical cat states is crucial to implement complex quantum information tasks based on them. Here, two optical cat states are prepared simultaneously based on a nondegenerate optical parametric amplifier. By subtracting one photon from each of two squeezed vacuum states, two odd cat states with orthogonal superposition direction in phase space are prepared simultaneously, which have similar fidelity of 60% and amplitude of 1.2. Compared with the traditional method to generate two odd optical cat states based on two degenerate optical parametric amplifiers, only one nondegenerate optical parametric amplifier is applied in this experiment, which saves half of the quantum resources of nonlinear cavities. The presented results make a step toward preparing the four-component cat state, which has potential applications in fault-tolerant quantum computation.     

Nonclassical properties of odd and even elliptical states

As a generalization of the optical circular states, elliptical states which are quantum superposition of coherent states on an ellipse in the α plane are constructed. The statistical properties of the states are investigated by using sub-Poissonian photon statistics, quadrature squeezing, Wigner function and phase distribution. It is shown that the elliptical states exhibit stronger quadrature squeezing. The interference fringes between the coherent states form the elliptic annuli of Fock states in the Wigner function picture. The phase distribution is no longer uniform as the circular states. An experimental scheme is proposed for generating equidistant coherent-state superpositions on an ellipse for the motion of the center of mass of a trapped ion.     

任意两个相干态的叠加态的相位分布和Wigner函数(英文)

从相位分布和Wigner函数两个方面研究了任意两个相干态|β〉and |mβeiδ〉的叠加态的量子统计性质.结果表明这种叠加态的非经典特性与β2,振幅系数m,相干态间的位相差δ以及叠加系数间的位相差都有关.当参量选择合适,这种叠加态存在着量子效应.计算了两个相干态等几率混合系综的相位分布和Wigner函数,经过与前者比较,结果表明由于相干项的存在,使得叠加态具有很好的量子力学行为.     

任意两个相干态的叠加态的相位分布和Wigner函数

从相位分布和Wigner函数两个方面研究了任意两个相干态|β〉 and |mβeiδ〉的叠加态的量子统计性质.结果表明这种叠加态的非经典特性与β2,振幅系数m,相干态间的位相差δ以及叠加系数间的位相差都有关.当参量选择合适,这种叠加态存在着量子效应.计算了两个相干态等几率混合系综的相位分布和Wigner函数,经过与前者比较,结果表明由于相干项的存在,使得叠加态具有很好的量子力学行为.     

Generation of a superposition of odd photon number states for quantum information networks

We report on the experimental observation of quantum-network-compatible light described by a nonpositive Wigner function. The state is generated by photon subtraction from a squeezed vacuum state produced by a continuous wave optical parametric amplifier. Ideally, the state is a coherent superposition of odd photon number states, closely resembling a superposition of weak coherent states |alpha > - |-alpha >. In the limit of low squeezing the state is basically a single photon state. Light is generated with about 10,000 and more events per second in a nearly perfect spatial mode with a Fourier-limited frequency bandwidth which matches well atomic quantum memory requirements. The generated state of light is an excellent input state for testing quantum memories, quantum repeaters, and linear optics quantum computers.     

Generating a Squeezed‐Coherent‐Cat State in a Double‐Cavity Optomechanical System

A squeezed‐coherent‐cat state (SCCS) in a mechanical system not only plays an important role for macroscopic quantum coherence, but also can be a carrier for quantum information. A scheme to generate a SCCS in a two‐mode optomechanical system is proposed, in which the modulated hopping interaction of two cavities is introduced. The two cavity modes couple with the same mechanical mode with linear and quadratic interaction, respectively. The SCCS is analytically deduced under an appropriate initial state, and the average phonon number and the parameter of squeeze are numerically calculated. Wigner function shown the properties of superposition and squeezing is plotted. Including the dissipation of the environment, the results show that a high quality mechanical resonator and a low noise environment are required to obtain high fidelity.     

Nonclassical state via superposition of two coherent states (π/2 out of phase) and related entangled states

Nonclassical features of the superposition of two coherent states which are π/2 out of phase are discussed, such as sub-Poissonian photon statistics and quadrature squeezing, as well as negativity of the Wigner function. Special nonclassicality is found in the special state where the relative phase of superposition has relationship with the average photon number. The analysis of the amount of entanglement is also presented for the related two-mode entangled coherent states.     

真空场注入非对称五态叠加多模泛函叠加态的高次振幅压缩

构造了由多模真空态、多模泛函相干态、多模泛函相干态的相反态、多模复共轭泛函相干态和多模复共轭泛函相干态的相反态这五个宏观上完全可分辩的量子态线性叠加所构成的强度不等的非对称五态叠加多模泛函叠加态光场|Ψ(5)vas〉q.利用多模压缩态理论,首次研究了态|Ψ(5)vas〉q的广义非线性等幂奇数次高次振幅压缩特性.结果发现:在一定的条件下,态|Ψ(5)vas〉q可呈现任意次的广义非线性等幂次高次振幅压缩效应,其压缩程度、压缩深度和压缩幅度与压缩次数、腔模总数、态间叠加几率幅、各模光场的经典强度以及经典初始相位的空间分布函数等强烈地非线性相关联;特别是,在特定条件下,真空场的注入可以提高压缩程度.