Higher-order properties of photon-added coherent states

We have studied a higher-order squeezing and a higher-order sub-Poissonian photon statistics in photon-added coherent states. We obtained analytic forms of the degree of higher-order squeezing and the degree of higher-order sub-Poissonian statistics. We show that the photon-added coherent state |α,m〉 exhibits both higher-order squeezing and higher-order sub-Poissonian character. For two different types of higher-order squeezing, the degree of squeezing becomes bigger when the added photon number is increased. In single-photon-added coherent state, the degree of squeezing depends upon the order of squeezing N. When N is increased, the degree of squeezing becomes bigger in the Hong-Mandel-type higher-order squeezing but becomes smaller in the Hillery-type higher-order squeezing. Also, the higher-order sub-Poissonian character is more pronounced than the usual sub-Poissonian character in the single-photon-added coherent state.     

Superposition of two coherent states π out of phase with average photon number as relative phase

This paper discusses nonclassical features of the superposition of two coherent states π out of phase with each other and parameterized solely by amplitude α, that is, when the relative phase has a relationship with average photon number ∣α∣². In particular, it discusses oscillatory and sub-Poissonian photon statistics, degree of quadrature squeezing, and quasiprobability distribution functions. We examine that some nonclassical properties of these states are different from those of the even and odd coherent states.     

Stimulated light backscattering from exciton Bose condensate

A new effect—light backscattering from exciton Bose-condensate—is considered. This effect is connected with the photoinduced coherent recombination of two excitons in the condensate with the production of two photons with opposite momenta. The effect of two-exciton coherent recombination leads also to the appearance of the second-order coherence in exciton luminescence connected with squeezing between photon states with opposite momenta. The estimations given for Cu₂O and GaAs excitons show that the effect of stimulated light backscattering can be detected experimentally. Moreover, in the system of 2D excitons in coupled quantum wells, the effect of stimulated anomalous light transmission must also take place. Anologous effects can also take place in systems of Bose-condensed atoms in excited (but metastable) states.     

Photon Excitations Excitated the Sqeezing Properties of the Excited Entangled Coherent States

In our previous paper, we have introduced a new kind of continuous-variable-type entangled states, called double-mode excited entangled coherent states. In this paper, we study sum squeezing properties of such excited entangled coherent states. We focus on discussing the influence of photon excitations on sum squeezing properties. It is found that the photon excitations seriously affected sqeezing properties of the excited entangled coherent states. With increasing the number of the photon excitations m, the higher-order terms move away from its initial state |ψ ₀〉 and the degrees of sum squeezing are increasing. In this sense, it implies that the photon excitations excitated the sum sqeezing properties of the double-mode excited entangled coherent states.     

Nonclassicality of two-mode nonorthogonal states

Nonclassical features of Schrödinger cat state with two-mode superposition state based on two coherent states π out of phase by fixing the relative phase equal to average photon number are discussed. Study of two-mode quadrature squeezing, oscillatory and sub-Poissonian photon statistics show that nonclassicality exists for these states. However, it is observed that the considered states do not violates the Cauchy–Schwarz inequality. Furthermore, simultaneously existence of quadrature squeezing and sub-Poissonian photon statistics shows that these states have more nonclassical features than that of famous even and odd coherent states.     

A proposal for experimental detection of amplitude nth-power squeezing

Recently, in several theoretical investigations, amplitude nth-power squeezing has been studied with n = 2, 3, 4, 5. In the present paper, we give a proposal for experimental detection of amplitude nth-power squeezing using ordinary homodyning with coherent light for arbitrary power n and discuss in detail its theory. The proposed scheme requires only repeated measurements of the factorial moments of number of photons in the light obtained after homodyning, with various shifts of phase of coherent light, and involves no approximations, whatsoever. This has advantage over the method proposed by Shchukin and Vogel [Phys. Rev. A 72 (2005) 043808] in that our method requires only one beam splitter and only one photodetector, and also lesser number of repetitions of experiment with phase-shifted coherent light.     

真空态多光子Jaynes—Cummings模型中场的振幅N次方压缩

本文研究了一初始处于原子相干态的二能级原子与真空态场相互耦合的ｋ光子Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ模型中场的振幅Ｎ次方程压缩特性。结果表明，场不仅存在振幅Ｎ＝ｋ次方压缩，而且当ｋ为偶数时，还存在振幅Ｎ＝ｋ／２次方压缩。     

Photon Modulated Coherent States of a Generalized Isotonic Oscillator by Weyl Ordering and their Non-Classical Properties

We construct photon modulated coherent states of a generalized isotonic oscillator by expanding the newly introduced superposed operator through Weyl ordering method. We evaluate the parameter A ₃ and the s-parameterized quasi probability distribution function to confirm the non - classical nature of the states. We also calculate the identities related with the quadrature squeezing to explore the squeezing property of the states. Finally, we investigate the fidelity between the photon modulated coherent states and coherent states to quantify the non-Gaussianity of the states. The constructed states and their associated non - classical properties will add further knowledge on the potential.     

Jaynes-Cummings模型中辐射场的振幅N次方压缩特性

本文研究了一初始处于激发态的二能级原子与相干态光场相互耦合的Jaynes-Cummings模型中场的振幅N次方压缩特性,给出了其压缩度随光场的初始平均光子数和压缩阶数的变化规律。     

Jaynes－Cummings模型中辐射场的振幅N次方压缩特性

本文研究了一初始处于激发态的二能级原子与相干态光场相互耦合的Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ模型中场的振幅Ｎ次方压缩特性，给出了其压缩度随光场的初始平均光子数和压缩阶数的变化规律。     

Squeezing and sub-Poissonian effects up-to fourth order in fifth harmonic generation

The concept of squeezing of the electromagnetic field is investigated in fundamental mode in fifth harmonic generation with the approximation |gt|²?1, where g is coupling constant and t, the interaction time between waves during the process. It has been found that squeezing occurs in amplitude, amplitude-squared, amplitude-cubed and fourth-order amplitude states of the field for selective phase values of field amplitude of fundamental mode. The dependence of squeezing on the photon number has also been investigated and found to be sub-Poissonian in nature. The signal to noise ratio has been studied in different order. It is found that the signal to noise ratio is higher in lower order.     

交流斯塔克效应对简并喇曼过程场振幅N次方压缩的影响

用改进型有效哈密顿量方法研究简并喇曼过程中辐射场的振幅N次方压缩。发现如果场初始处于相干态,则它以后不会获得任何次方的压缩。如果场初始处于压缩真空态,则它以后可获N次方压缩。讨论了场涨落对次幂N、初场平均光子数n和压缩角ξ的依赖关系。     

频率变化场与原子相互作用系统中原子的信息熵压缩

利用J-C模型,考虑场频率随时间以正弦函数形式作小量变化,在旋波近似下,研究了二能级原子与单模辐射场相互作用系统中原子的信息熵压缩特性.利用数值计算方法给出原子的信息熵压缩因子随时间的演化曲线.研究结果表明:原子的信息熵仅在演化的初期呈现压缩效应,初始的原子分布角、光场强度和场频率随时间的变化对原子的信息熵压缩有明显影响.场频率随时间的变化对原子的信息熵压缩因子的演化具有调制作用,随场频率变化的幅值增大,调制作用增强,压缩效应减弱.     

三能级原子与奇偶纠缠相干光作用的光场压缩

采用求解薛定谔方程和数值计算方法,研究了V型三能级原子与双模奇偶纠缠相干光场相互作用过程中的光场压缩效应,讨论了压缩效应与双模奇偶纠缠相干光场的纠缠程度、系统失谐量、双模光场的平均光子数和原子基态概率幅的依赖关系。结果表明：光场压缩效应与双模奇偶纠缠相干光场的纠缠程度、失谐量、平均光子数和原子初态相关联：双模纠缠相干光场处于非纠缠状态时的光场压缩量比光场处于纠缠状态时要大;原子处在单纯的基态或激发态时光场都有明显的压缩现象出现;而原子初态中基态和激发态的概率幅较接近时无光场压缩现象;无论光场是否处于纠缠态,只有两模平均光子数接近时,光场才会出现压缩效应。     

奇偶q-变形相干态的高阶压缩效应

研究了奇偶q变形相干态中光场的高阶压缩效应.数值计算结果发现,奇偶q变形相干态中光场的高阶压缩效应与参数值q有关,当参数q取偏离1较大的值时,q变形奇偶相干态均可具有奇次方阶压缩效应却无偶次方阶压缩效应,这与通常奇偶相干态的压缩特性是不同的 关键词： 光场 q变形相干态 高阶压缩效应     

Exciton correlations and input–output relations in non-equilibrium exciton superfluids

The photoluminescence (PL) measurements on photons and the transport measurements on excitons are the two types of independent and complementary detection tools to search for possible exciton superfluids in electron–hole semi-conductor bilayer systems. In fact, it was believed that the transport measurements can provide more direct evidences on superfluids than the spectroscopic measurements. It is important to establish the relations between the two kinds of measurements. In this paper, using quantum Heisenberg–Langevin equations, we establish such a connection by calculating various exciton correlation functions in the putative exciton superfluids. These correlation functions include both normal and anomalous greater, lesser, advanced, retarded, and time-ordered exciton Green functions and also various two exciton correlation functions. We also evaluate the corresponding normal and anomalous spectral weights and the Keldysh distribution functions. We stress the violations of the fluctuation and dissipation theorem among these various exciton correlation functions in the non-equilibrium exciton superfluids. We also explore the input–output relations between various exciton correlation functions and those of emitted photons such as the angle resolved photon power spectrum, phase sensitive two mode squeezing spectrum and two photon correlations. Applications to possible superfluids in the exciton–polariton systems are also mentioned. For a comparison, using conventional imaginary time formalism, we also calculate all the exciton correlation functions in an equilibrium dissipative exciton superfluid in the electron–electron coupled semi-conductor bilayers at the quantum Hall regime at the total filling factor ν_T=1${\nu }_T=1$. We stress the analogies and also important differences between the correlations functions in the two exciton superfluid systems.     

光子湮没算符高次幂本征态的压缩性质

本文研究光子湮没算符高次幂α^k(k≥3)的k个正交归一本征态的压缩性质,发现当k为偶数时,这些本征态均可有振幅N次方(k=2N)压缩存在。 关键词：     

Higher-order squeezing and sub-poissonian photon statistics in CARS and CAHRS

The Squeezing and sub-poissonian photon statistics of an optical field are a purely quantum mechanical phenomenon and has been accepted as means of achieving noise below the quantum shot-noise limit. The effect of higher-order squeezing and sub-poissonian nature of an optical field in coherent anti-Stokes Raman scattering (CARS) and coherent anti-Stokes hyper Raman scattering (CAHRS) are investigated under short-time approximation. The coupled Heisenberg equations of motion involving real and imaginary parts of the quadrature operators are established and solved under short-time scale. The dependence of squeezing on the number of photons is also investigated. It is also shown that higher-order squeezing allows a much larger fractional noise reduction than lower-order squeezing. The occurrence of amplitude squeezing effects of the radiation field in the fundamental mode is investigated in both the processes. The present work shows that squeezing is greater in CAHRS than the corresponding squeezing in CARS. It is also shown that squeezing is greater in stimulated process than corresponding squeezing in spontaneous interaction. The conditions for obtaining maximum and minimum squeezing are obtained. The photon statistics of the pump mode in the processes has also been investigated and found to be sub-poissonian in nature.     

Entangled Finite Dimensional Pair Coherent States and Their Applications

Intermediate states of electromagnetic field are reviewed. It is a type of the correlated two-mode states (converter state). Based on the resonant ion-cavity interaction, we propose a scheme to generate these states revealing their connection with the converter state. The practical feasibility of this method is also discussed. We discuss nonclassicality of a finite dimensional pair coherent states in terms of sub-Poissonian photon statistics as well as the negativity of the Wigner function after deriving the analytic expression for the Wigner function. We explore a superposition of two finite dimensional pair coherent states. We show that such states possess inherent nonclassical properties such as sub-Poissonian distribution, anti-correlation between the two modes and violation of Cauchy-Schwarz inequalities. The s-parameterized characteristic function (CF) is considered. The phase distribution in the framework of Pegg and Barnett formalism, W-function and Q-function are discussed. Furthermore, a two-level atom in interaction with a two-mode quantized electromagnetic fields besides a frequency converter interaction initially prepared in an entangled two-mode coherent state is presented. Exact solution of the wave function in the Schrödinger picture is obtained. Some statistical aspects of this model are presented. The results are employed to perform a careful investigation of the temporal evolution of the atomic inversion, entropy squeezing and variance squeezing. General conclusions reached are illustrated by numerical results.     

Generalized Photon Added and Subtracted f-Deformed Displaced Fock States

In this paper, by making use of the nonlinear coherent states approach, the generalized photon added and subtracted f-deformed displaced Fock states are introduced. In other words, a natural link between photon added and subtracted displaced Fock states and nonlinear coherent states associated with nonlinear oscillator algebra is obtained. It is found that various kinds of nonclassical states can be generated by adopting appropriately controlling parameters in both linear and nonlinear regimes. Moreover, examining some of the most nonclassical properties such as Mandel's Q parameter, different types of squeezing, namely, quadrature, amplitude–squared and phase entropic squeezing, and Vogel's characteristic function, the nonclassicality features of the considered quantum states of interest are studied. Furthermore, to obtain the degree of quantum coherence, the relative entropy of coherence is investigated. Indeed, the nonclassicality aspects of the states obtained have been numerically studied to understand the roles of deformation functions, photons added and subtracted, and photon number occupied in the Fock state on physical properties. It is demonstrated that the depth and the domain of the nonclassicality features of the system can properly be controlled by selecting the suitable parameters.