Study of higher order non-classical properties of squeezed Kerr state

Recently, Prakash and Mishra [J. Phys. B: at. Mol. Opt. Phys., 39, 2291(2006); 40, 2531(2007)] have studied higher order sub-Poissonian photon statistic conditions for non-classicality in the form of general inequalities for expectation values of products of arbitrary powers of photon number and of photon-number fluctuation. It is, therefore, vital to study the generation of these higher order sub-Poissonian photon statistics (phase-insensitive behavior) in a physically realizable medium and their relations to higher order squeezing (phase-sensitive behavior). In the present paper, we study higher order non-classical properties, such as Hong and Mandel squeezing, amplitude-squared squeezing and higher order sub-Poissonian photon statistics, of squeezed Kerr state which is generated by squeezing the output of a Kerr medium whose input is coherent light. Such states can be realized if laser light is sent through an optical fiber and then into a degenerate parametric amplifier. It is established that the squeezed Kerr state can exhibit higher order non-classical properties.     

Analytical approach of using squeezed state formation of light for conducting all-optical noise free NAND logic operation

We report a new all-optical noise free NAND logic operation using squeezed state of light with high speed of operation. The squeezed state of light generated by means of optical parametric amplification (OPA). The lights were generated in the same way to maintain the same characteristics. Balance homodyne detection scheme is utilized to detect the squeezed state of light. It is one of the promising squeezed light based devices for the next generation logic optical circuits.     

基于量子增强型光纤马赫-曾德尔干涉仪的低频信号测量

利用低频光通信波段真空压缩态光场可实现基于光纤的量子精密测量.本文利用简并光学参量振荡器实验制备出1550 nm低频真空压缩态光场.在分析频段10—500 kHz范围内压缩态光场的压缩度均达3 dB.用实验制备的1550 nm真空压缩态光场填补光纤马赫-曾德尔干涉仪的真空通道,实现了量子增强型光纤马赫-曾德尔干涉仪,完成了突破标准量子极限的相位调制频率为500 kHz的低频信号测量.与光纤马赫-曾德尔干涉仪相比,测量信噪比提高了2 dB.     

基于低频压缩光的声频信号测量

低频信号测量在引力波探测、生物成像及磁场测量等方面具有重要的应用价值.本文利用非简并光学参量放大器获得了低频压缩态光场,在频率19 kHz处直接测到的压缩度为(7.1±0.1)dB;将产生的正交位相压缩态光场注入到马赫-曾德尔干涉仪中,实现了超越散粒噪声极限(3.0±0.4)dB的声频相位信号的测量.本实验的开展为低频压缩光的产生及基于低频压缩光的声频信号测量提供了一定技术支撑,并且此技术有望扩展到磁场、空间小位移等其他物理量的量子精密测量方案中.     

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.     

基于压缩光的量子激光雷达技术

利用Wigner函数对真空态、单光子态、压缩态在相空间的噪声分布进行仿真,并系统分析了基于压缩光的量子相干激光雷达和压缩光注入式量子激光雷达.研究表明,相比经典激光雷达,较高压缩度有利于量子相干激光雷达探测信噪比的提升,理论上8dB的压缩度可以使信噪比提高6.25倍;而压缩光注入式量子激光雷达系统的空间分辨率主要取决于真空压缩光的压缩度和无噪声相敏放大系统的增益.由于压缩光对探测信噪比的提升作用,量子激光雷达在微弱信号探测和高分辨率成像领域具有显著优势.     

Experimental generation of optical non-classical states of light with 1.34 <Emphasis Type="Italic">μ</Emphasis>m wavelength

We report the experimental generation of the optical non-classical states with 1.34 μm wavelength which is close to one of the fiber telecommunication windows (1.31 μm). The single-mode amplitude squeezed states with quantum fluctuation of 2.3 ± 0.1 dB below the shot noise limit (SNL) and the entangled states with quantum correlation of 1.1 ± 0.1 dB below the SNL are produced by an optical parametric amplifier with a type-I phase-matched PPKTP crystal and a pair of properly oriented type-II phase-matched KTP crystals, respectively.     

Analytical investigation on interactions among squeezed vacuum and coherent state,coherent vacuum and squeezed state,and among phase squeezed and amplitude squeezed states of light

Squeezed state of light has drawn an enormous attention in information processing and digital communication since it has broken the quantum limit of noise. Here we have analytically investigated the interactions among coherent and vacuum squeezed states of light, interaction among coherent vacuum and squeezed states of light, and that between phase and amplitude squeezed states of light signals. Hence we established the nature of the resulting interaction with the help of photon statistics.     

双能态自旋-晶格声子耦合量子隧道系统的非经典能态和量子相干耗散

采用关联表象变分波函数方案, 介入三个非经典关联效应, 求解有限温度双能态自旋-晶格声子耦合量子隧道系统的非经典态, 着重研究化解由于粒子自旋-单声子相互作用引起的量子涨落导致双能态系统的退相干性量子耗散. 这三个非经典关联效应是: 1) 声子位移-粒子自旋 (σ_z)间强非绝热关联; 2) 声子压缩态效应及其伴随发生的单声子相干态-声子压缩态两过程相干效应; 3) 由关联表象导致的声子位移(U_D)与声子压缩(U_S)的表象关联非绝热修正. 结果表明: 由于引入粒子自旋-双声子相互作用, 大幅度地增强了声子场压缩态, 特别是更进一步极大幅度地增强了非经典压缩-相干态效应. 因此, 由粒子自旋-单声子相互作用产生的Debye-Walle相干弹性散射效应导致量子隧道项(-Δ₀σ_x)的强烈指数衰减及其伴随严重的量子相干损失的极大幅度的抑制, 并且自旋-晶格声子耦合量子隧道系统的非经典态能量大幅度降低. 关键词： 非经典能态 量子隧穿相干损失 自旋-双声子相互作用 压缩相干态效应     

Generation of pulsed squeezed light in a mode-locked optical parametric oscillator

The generation of pulsed squeezed light using an optical parametric oscillator (OPO) is discussed. This mode-locked optical parametric oscillator consists of a nonlinear crystal in a cavity which is resonant for both signal and idler waves and which is synchronously pumped by the second-harmonic of an acousto-optically mode-locked cw Nd: YAG laser. The fundamental wavelength of the pump laser provides local oscillator pulses for balanced homodyne detection of squeezed vacuum pulses emitted by the oscillator when operated below oscillation threshold. Photocurrent noise reduction to 30% below the classical shot-noise limit is observed, corresponding to squeezing of the field to a level approximately a factor of two below the mean square vacuum noise.     

对应于铯原子D1线连续可调谐正交压缩态光场的制备

铯原子D₁线的非经典光由于其波长接近于量子点的独特优势,在固态量子信息网络的发展中有着重要的应用前景.在之前的工作中,利用两镜连续简并光学参量振荡器中的参量下转换过程,制备出2.8 d B正交压缩真空态光场.然而,所产生光场的压缩度较低,对于对压缩光具有实用意义的可调谐性能也未做进一步探究.理论分析表明,光学参量振荡器后腔镜对信号光透射率的增加及内腔损耗的减小可以提高压缩度.因此,本文在该研究基础上,通过使用高光洁度腔镜及优化腔镜镀膜参数等方式对光学参量振荡器进行改良,降低了光学参量腔阈值,获得压缩度为3.3 d B的单模正交压缩真空光.当光学参量腔运转为参量反放大状态时,在系统稳定运行的情况下,制备的明亮压缩态光场能够连续调谐80 MHz,为其在量子信息网络中的应用奠定了良好的基础.     

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.     

带有电子-双声子相互作用的一维铁磁性介观环的非经典本征态和非经典本征持续电流

在一维铁磁性织构介观环的基础上, 计及电子-双声子相互作用, 介入了三项非经典效应抑制电子-单声子相互作用引起的量子涨落效应: 1) 跳步电子-单声子相干态关联效应;2) 由压缩相干态引起的声子压缩态-单声子相干态间过程关联效应;3) 声子位移-声子压缩态的表象关联效应．从结果来看, 电子-双声子相互作用明显加强了压缩效应(增大压缩参量), 而跳步电子-单声子相干态关联效应引起本征能量大幅度下降, 持续电流大幅度增加．特别是介入了声子压缩态-单声子相干态间过程关联效应后, 声子压缩参量远大于理想压缩态相应的压缩参量, 有效地抑制了Debye-Waller(D-W)效应．当声子压缩态-单声子相干态间过程关联与声子位移重整化效应结合在一起时, 声子场的压缩将更大幅度地增加, D-W效应(参量w_ph)将更大幅度地减小, w_ph << w_ph⁽⁰⁾, 从而极大幅度地抑制了电子-单声子相互作用导致的量子涨落效应. 这样一来, 非经典态本征能量E_n极大幅度地下降, E_n << E_n⁽⁰⁾, 与此同时, 本征持续电流振幅I_n 则极大幅度地增大, I_n >> I_n⁽⁰⁾.     

基于电磁诱导透明机制的压缩光场量子存储

光场的量子存储不仅是构建量子计算机的重要基础,而且是实现量子中继和远距离量子通信的核心部分.由于存在不可避免的光学损耗,光学参量放大器产生的压缩真空态光场将变为压缩热态光场,不再是最小不确定态.因此,压缩热态光场的量子存储是实现量子互联网的关键.在原子系综中利用电磁诱导透明机制能够实现量子态在光场正交分量和原子自旋波之间的相互映射,即受控量子存储.本文根据量子存储的保真度边界,研究了实现压缩热态光场量子存储的条件.量子存储的保真度边界是通过经典手段能够达到的最大保真度,当保真度大于该边界时,就实现了量子存储.通过数值计算分析了不同情况下压缩热态光场的量子存储保真度边界,以及存储保真度随存储效率的变化关系,得到了实现量子存储的条件,为连续变量量子存储实验设计提供了直接参考.     

极化激元系统时间演化的量子涨落特性和非经典统计行为

将极化激元系统约化成模型单模光子-TO声子有效相互作用系统， 在此基础上以解析形式讨论了系统的力学量、压缩态、量子涨落特性以及亚泊松分布等非经典效应的动力学演化行为.结果表明，光子场与极化波量子场彼此交换能量过程随时间演化呈振荡性质，光子场和声子场都可以演化成压缩态，其二阶压缩度随时间演化成复杂周期振荡特性，这种非经典特性是非线性相互作用的结果并且以k₁项和k₂项同时存在并相互关联为前提.而此时光子和声子统计分布随时间演化呈现介于超Poison分布和亚Poison分布之间复杂周期振荡的新结果，非线性作用k₁项和k₂项对这种非经典统计行为都有贡献. 关键词： 极化激元系统动力学演化 单模光场-TO声子有效模型哈密顿量 量子涨落与压缩态 亚泊松分布     

非简并双光子Jaynes-Cummings模型中贝尔非定域性的演化

基于赝自旋算符的关联所对应的贝尔算符期待值,研究了各种双模非经典态(纠缠相干态、对相干态以及双模压缩真空态)在非简并双光子Jaynes-Cummings模型中贝尔非定域性的动力学特性.结果表明:对于纠缠相干态,贝尔非定域性的演化与双模场平均光子数的大小息息相关;对于对相干态和双模压缩真空态,贝尔非定域性会在有限的时间内完全消失,之后又基本上复原到初始值,呈现出周期性振荡现象.     

量子光学中的非经典态

本文扼要地介绍了光子数态、热光场态、相干态、压缩态、相位态和中间态等。重点是介绍它们的物理性质。例如,指出相干态在谐振子座标表象中的表示就是带电谐振子在均匀电场中的基态波函数;它的时间演化波包的概率密度分布,形状不随时间变但中心位置随时间作周期振荡。文中对相干态和压缩态等提供了也许是一点新的看法：将相干态、压缩真空态、压缩相干态和相干压缩态等看作是一准玻色子的基态或相干态。而实现的手段可以是原来的幺正算符也可以是投影算符。这样的好处是：（１）对相干态和压缩态间的联系有更深的认识;（２）便于计算和进一步展开等等。文中还对各个态的压缩性、统计性等作了介绍,有的还用图表等演示了它们的非类经典特性。最后,文中还介绍了准概率分布函数、相空间技术以及它们的应用并给出了示例     

铷原子D1线真空压缩光场的产生及态重构

碱金属原子是光量子存储的良好介质,与碱金属原子共振的非经典光场是量子信息处理的重要资源.本文采用周期极化磷酸氧钛晶体作为非线性介质,利用参量振荡过程产生了795 nm(铷原子D1线)的真空压缩光场.通过对平衡零拍探测系统的时域信号进行采集,得到压缩光场不同相位角下的噪声分布;利用极大似然估计法对压缩光场进行了态重构,得到了密度矩阵及相空间的Wigner函数.理论计算了真空压缩场的光子数分布和Wigner函数,并对理论计算结果和极大似然重构结果进行了分析和比较.     

Schemes for performance of displacing Hadamard gate with coherent states

We propose an approach with displaced states to use it for rotations of base coherent states and squeezed coherent states. Our approach is based on representation of the coherent states in free-traveling fields in terms of displaced number states with arbitrary amplitude of displacement. Two optical schemes are developed for construction of Hadamard gate for the base states. One of the optical schemes is based on alternation of photon additions and displacement operators (in general case, N-photon additions and N?1-displacements are required) to generate displaced squeezed even/odd superposition of coherent states (SCSs) with high fidelity in dependency on type (computational zero or one) of the base input state. Another optical scheme uses two-photon subtracted squeezed coherent states to approximate outcome of the Hadamard gate for the base squeezed coherent states. Output states approximate with high fidelity either even squeezed SCS or odd SCS shifted relative to each other by some value. It enables to adjust the optical scheme for construction of the Hadamard gate being mainframe element for quantum computation with basic squeezed coherent states.     

Squeezing in the audio gravitational-wave detection band

We demonstrate the generation of broadband continuous-wave optical squeezing from 280 Hz-100 kHz using a below-threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise, and detuning fluctuations, present in optical parametric amplifiers, have negligible effect on squeezing produced by a below-threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational-wave detectors.