Quantum dynamics of interacting modes in the process of intracavity subharmonic generation

The dynamics of correlation between fluctuations of the number of photons of interacting modes is investigated for the process of intracavity subharmonic generation. It is demonstrated that this correlation strongly depends on the nonlinear mode coupling coefficient. For small values of the coupling coefficient, the correlation between fluctuations of the number of photons is small. With an increase in the coupling coefficient, the correlation increases (the state of subsystems becomes entangled) and, starting from a particular value of the coupling coefficient, starts to decrease with further increase in the coupling coefficient, gradually approaching zero (entanglement of subsystem states decreases). The quantum dynamics of the number of photons, quantum entropy, and Wigner function of the stationary state of the fundamental and subharmonic modes is investigated. It is demonstrated that the dynamics of these quantities also strongly depends on the coupling coefficient of the interacting modes. We show that, for large values of the mode coupling coefficient and long interaction times, the subharmonic mode becomes localized in a two-component state with equal probabilities of finding it in each component. Quantum entropy of this state is smaller than maximum entropy of the two-component state equal to ln2, which suggests that quantum-mechanical interference takes place between the subharmonic mode components.     

Quantum coherence and entangled states in intracavity third subharmonic generation process

The dynamics of correlation of photon number fluctuations of interacting modes for the process of intracavity third subharmonic generation is investigated. It is shown that the entangled field states by the variables of photon number can be obtained in this system. The quantum dynamics of the photons number, the quantum entropy and the Wigner function of the stationary states of the fundamental mode and the third subharmonic mode have also been studied. It is found that the dynamics of these quantities depends highly on the value of the coupling coefficient of the interacting modes. It is shown that at long interaction times and for the large values of the coupling coefficient of the modes, the mode of the third subharmonic is localized in the three-component state with the same probability of detection of the mode in each component of the state. The quantum entropy of the state is less than the maximal entropy of the three-component state ln3, which points out the presence of quantum mechanical interference between the components of the state of third subharmonic mode.     

Statistical Properties of Photon-Added Two-Mode Squeezed Coherent States

The nonclassical and non-Gaussian quantum states—photon-added two-mode squeezed coherent states have been theoretically introduced by adding multiple photons to each mode of the two-mode squeezed coherent states. Starting from the new expression of two-mode squeezing operator in entangled states representation, the normalization factor is obtained, which is directly related to bivariate Hermite polynomials. The sub-Poissonian photon statistics, cross-correlation between two modes, partial negative Wigner function are observed, which fully reflect the nonclassicality of the target states. The negative Wigner function often display non-Gaussian distribution meanwhile. The investigations may provide experimentalists with some better references in quantum engineering.     

Dynamics of Entropy Production Rate in Two Coupled Bosonic Modes Interacting with a Thermal Reservoir

The Markovian time evolution of the entropy production rate is studied as a measure of irreversibility generated in a bipartite quantum system consisting of two coupled bosonic modes immersed in a common thermal environment. The dynamics of the system is described in the framework of the formalism of the theory of open quantum systems based on completely positive quantum dynamical semigroups, for initial two-mode squeezed thermal states, squeezed vacuum states, thermal states and coherent states. We show that the rate of the entropy production of the initial state and nonequilibrium stationary state, and the time evolution of the rate of entropy production, strongly depend on the parameters of the initial Gaussian state (squeezing parameter and average thermal photon numbers), frequencies of modes, parameters characterising the thermal environment (temperature and dissipation coefficient), and the strength of coupling between the two modes. We also provide a comparison of the behaviour of entropy production rate and Rényi-2 mutual information present in the considered system.     

Kerr介质腔中非线性J-C模型的腔场谱

研究了Kerr介质腔中非线性J-C模型的腔场谱.导出了初始光场处于任意量子态时腔场谱的计算公式,给出了光场处于数态、相干态和压缩真空态时的数值结果,讨论了Kerr效应和初始场强对腔场谱的影响.发现在光子数态的情况下,n≠1时均为2峰结构,Kerr介质使得中心频率按x(2n-1)的规律向高频方向移动,并破坏谱结构的双峰对称性;在相干态和压缩真空态情况下,当Kerr效应较弱时,非线性J-C模型中腔场谱的非经典特性较为突出,Kerr效应较强时,呈现多峰结构,谱的结构特征主要由Kerr效应决定,由于原子与腔场的耦合被抑制,腔场谱的非线性特征趋于消失.     

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.     

Wigner distribution of elliptical quantum optical vortex

We calculate the Wigner quasiprobability distribution function of the quantum elliptical vortex in elliptical beam (EEV), produced by coupling squeezed coherent states of two modes. The coupling between the two modes is performed by using beam splitter (BS) or a dual channel directional coupler (DCDC). The quantum interference due to the coupling between the two modes promises the generation of controlled entanglement for quantum computation and quantum tomography.     

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.     

Nonclassical Properties of Multiple-Photon-Added Two-Mode Squeezed Coherent States

We investigate how the photon addition operation affects the nonclassical properties of the non-Gaussian squeezed state generated by adding photons to each mode of the two-mode squeezed coherent state (TMSCS). By the generating function of two-variable Hermite polynomials, the compact expression of normalization factor is derived. We show that the fields in such states exhibit remarkable sub-Poissonian photon statistics. The photon addition operation can enhance the cross-correlation for appropriate combinations of several parameters involved in the TMSCS. Compared with that of TMSCS, the Wigner function of the photon–added TMSCS (PA-TMSCS) is modulated by a factor which is also related with two-variable Hermite polynomials. Such Wigner functions have some negativity regions and show a strong quantum mechanical interference. In addition, the normalization factor, Mandel’s Q parameter, cross-correlation function and Wigner functions are all sensitive to the compound phase involved in TMSCS.     

Cavity Field Spectra of the Intensity-Dependent Two-Mode Jaynes–Cummings Model

The cavity field spectrum of a two-level atom interacting with two modes of the radiation field through intensity-dependent coupling in an ideal cavity is investigated. The results for the initial fields in pure number states, coherent states, and squeezed vacuum states are calculated. We find that the frequency of one mode is tuned by the intensity of the other mode when the two modes are both in pure number states or coherent states. A complicated multipeak structure appears when both field modes are in a superposition of number states initially.     

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.     

双模相干态和压缩真空态光场-非等同两原子体系的腔场谱

研究了两个非等同二能级原子与双模腔场相互作用过程的腔场谱.导出了双模初始光场处于任意量子态时腔场谱的计算公式,给出了光场处于相干态和压缩真空态时的数值结果,讨论了相对耦合常数R=g2/g1和初始场强对腔场谱的影响.发现相干态光场的腔场谱在R很小时为双峰,在R接近于1时为3峰.压缩真空态的腔场谱在弱场条件下表现为复杂的多峰结构,在强场条件下则只有单一经典共振峰或裂距很小的双峰.     

Thermo Vacuum State for Describing the Density Operator of Photon-subtracted Squeezed Chaotic Light

For the density operator describing s?photon-subtracted squeezed chaotic light (PSSCL) we search for its thermo vacuum state (a pure state) in the real-fictitious space. We find that it reduces to a thermo vacuum state of squeezed chaotic light when s = 0, and to a thermo vacuum state of the optical negative binomial field when no squeezing. The new thermo vacuum state simplifies calculating photon number average, quantum fluctuation and Mandel’s Q parameter of PSSCL. Using the method of integration within ordered product (IWOP) of operators we also derive the normalization coefficient and explicitly analytical expressions of Wigner function for PSSCL.     

Quantum dynamics of formation of an unstable field state in the process of intracavity third-harmonic generation

The dynamics of the Wigner functions and quantum entropy of the fundamental and third-harmonic modes is studied for the process of intracavity third-harmonic generation. It is shown that quantum dynamics of the system strongly depends on the coupling coefficient of the interacting modes. The dynamics of the transition of the system from a stable to an unstable state is investigated.     

单模辐射场与耦合双原子相互作用系统中场熵的压缩特性

研究了单模辐射场与耦合双原子相互作用系统中场熵的压缩特性,讨论了系统初始状态及原子间偶极相互作用对场熵压缩特性的影响.数值计算结果表明,当系统初始时刻处于合适的相干叠加态时,场熵呈现出周期性压缩现象,其压缩深度和压缩时间与原子间偶极相互作用强度有关. 关键词： 单模辐射场 耦合双原子 光场熵压缩     

耦合双原子Jaynes-Cummings模型的腔场谱H

研究了处于激发态的两原子与高Q腔场相互作用单光子过程的腔场谱,给出了初始光场为光子数态、相干态、压缩真空态时的腔场谱数值计算结果,分析了原子间偶极-偶极相互作用强度gα对腔场谱结构的影响.发现真空场Rabi峰,当gα较弱时为4峰,gα较强时为3峰结构;弱场数态(n＞0)时为5峰,强场时为3峰结构.相干态和压缩真空态时,谱结构与光子数分布有关,一般为复杂的多峰结构.结果表明,gα对峰位峰高都有影响,破坏了谱结构的对称性,但这种影响只在真空场和弱场时才较明显.     

Photon Statistics of Generic Two-Mode Squeezed Coherent Light

for two-mode squeezed coherent states, the photon distribution function is expressed in terms of both four-variable and two-variable Hermite polynomials depending on two squeezing parameters, the relative phase between the two oscillators, their “spatial” orientation, and a four-dimensional shift in phase space of the electromagnetic field oscillator. The oscillations of the photon distribution function are discussed. The Wigner function and Q-function of the generic two-mode squeezed vacuum and squeezed coherent state are calculated explicitly.     

Nonlinear Tripartite Entangled State Representation and Related Generalized Wigner Function

We construct the nonlinear tripartite entangled state representation and the related generalized Wigner operator. Then we discussed the Wigner functions of the nonlinear tripartite entangled state and the three-mode nonlinear squeezed vacuum state, and obtained the classical Weyl corresponding function of the three-mode nonlinear squeezed state.     

Nonlinear Tripartite Entangled State Representation and Related Generalized Wigner Function

We construct the nonlinear tripartite entangled state representation and the related generalized Wigner operator. Then we discussed the Wigner functions of the nonlinear tripartite entangled state and the three-mode nonlinear squeezed vacuum state, and obtained the classical Weyl corresponding function of the three-mode nonlinear squeezed state.     

Single-mode photon number measurement for the squeezed two-mode number state

Based on the fact that a two-mode squeezed number state is a two-variable Hermite polynomial excitation of the two-mode squeezed vacuum state, the result of one-mode l-photon measurement for the two-mode squeezed number state $S_2|m,n\rangle$ is discussed. It is found that a remaining field-mode simultaneously collapses into a number state $|n-m+l\rangle$ with the coefficient being a Jacobi polynomial of n, m and l, which manifestly exhibits the entanglement between the two modes, i.e. it depends on the number-difference between the two modes. The second mode collapses into an excited coherent state when the first mode is measured as a coherent state.