Steady-state populations of a driven three-level atom in a broad-band squeezed vacuum

A theoretical study is made of the steady-state populations of a three-level atom in a ladder configuration, driven by a superposition of a monochromatic laser wave with a broad-band squeezed vacuum. The master equation for the system and the atomic Bloch equations are derived. The steady-state populations are calculated numerically and shown graphically as functions of two-photon detuning for various cases of the squeezed vacuum. It is shown that, the atomic populations depend strongly on the relative phase of the driving field and the squeezed vacuum. When the phase matching condition is fulfilled, there will be a strong two-photon resonant absorption from the squeezed vacuum, a characteristic different from absorption of photons from a classical field. Received: 28 May 1997 / Revised and Accepted: 10 December 1997     

Evolution equations of the expected phase space ion densities and correlation functions in a D+T plasma

Summary In this paper we formualte a master equation approach describing a D+T thermonuclear plasma in a lumped phase space. From the first moments of this master equation and performing the pass to the continuous limit the evolution equations for the expected phase space ion densities emerge. Also we have obtained the evolution equations of the equal time correlation and covariance functions. Finally we have deduced the hydrodynamic equations that arise from a master equation approach.     

非平衡系统的概率模型及Master方程的建立

针对非平衡态统计中出现的非线性及多元线性Master方程,明确提出了一般的概率假定;应用概率论的方法建立了一般的非线性及多元线性Master方程;讨论了它们与宏观动力学方程的一致性问题;最后应用多元线性Master方程讨论了Brusselator的涨落,并对其耗散结构的产生作了初步解释。 关键词：     

Feasibility study of pulse compression by two-photon self-induced transparency

The possibility of pulse compression by the process of two-photon self-induced transparency (TPSIT) is considered. Numerical solutions to the two-photon Bloch-Maxwell equations are presented, and limits established for the maximum amount of detuning from exact resonance for which the compression process will still occur.     

Non-Markovian and Markovian Dynamics of a V-type Three-Level Atom

The reduced dynamics of a V-type three-level atom in a structure reservoir is presented,which has the exact solution in certain special condition.The Markovian and non-Markovian master equations for this composite system are solved and compared with the exact solution.The solving approach can be directly generalized to the solution of a V-type multilevel system dynamics interacting with a reservoir.The results further testify that these two kinds of master equations are exploited in different coupling regime,providing guidance for further application of these variants master equations to solve multilevel system dynamics without the exact solution.     

Phenomenological approach to classical and quantum relaxation of the harmonic oscillator

A phenomenological approach for construction of the Markovian master equation describing the relaxation of the harmonic oscillator to the equilibrium at temperatureT is presented. A superoperator formalism built up by analogy with the second quantization method of quantum mechanics is proposed for the formulation of both the classical and quantum master equations. The quantum-field-theoretical methods are used for the calculation of the mean values of the physical quantities and for the solution of the master equations.     

Optical Two-Photon Surface Nonlinear Waves

A theory of the optical surface two-photon small-amplitude breather in a multilayer system of the isotropic and anisotropic left-hand metamaterials, when there are a graphene monolayer (graphene-like twodimensional material) and a transition layer with impurity optical atoms (semiconductor quantum dots), is constructed. It is shown that the system of constitutive equations for two-photon transitions and wave equation for a surface plasmon–polariton TM mode are reduced to the nonlinear Schrödinger equation with damping. Explicit analytical expressions for a surface two-photon small-amplitude self-induced transparency breather (0π-pulse) are obtained. It is shown that the optical conductivity of graphene leads to the exponential damping of intensity of a surface two-photon nonlinear wave during the propagation. One- and two-photon small-amplitude breathers in graphene are compared, and it is shown that differences between their parameters are substantial.     

双光子吸收过程中光场振幅平方压缩

本文由双光子过程主方程运用生成函数法,求得双光子吸收过程光场振幅平方压缩的表示式,讨论振幅平方压缩随无量纲时间τ,入射光场相位角θ及平均光子数|α|²的变化情况。双光子吸收过程是产生振幅平方压缩效应的有效途径。最后论证振幅平方压缩效应的独立性。 关键词：     

压缩真空库场中二能级原子的非简并双光子荧光谱

利用投影算符技巧从刘维方程出发导出了二能级原子约化密度算符主方程，研究了压缩真空库场中二能级原子的非简并双光子荧光谱特性.发现与真空库或热库中双光子荧光不同，在非简并双光子情况中存在一种新型振荡现象，它具有上下两个阈值，在上下阈值之间原子发生振荡，在两阈值之外原子将不发生振荡.在两阈值之间原子的非简并双光子荧光谱呈现正峰结构，在两阈值之外双光子荧光谱具有负的峰结构.光谱形状强烈地依赖于双光子自然线宽，但光谱是非相敏性的，这是未曾预料到的. 关键词：     

The low-energy compton scattering and polarizability of spin-0 Hadrons in a Gaugeinvariant approach

In this work, the amplitude of the interaction of an electromagnetic field with π-mesons has been determined in the context of a relativistic gauge-invariant approach by solving electrodynamic equations with the use of the covariant Green’s function method. Based on this approach, the effective Lagrangian of the two-photon interaction with spin-0 hadrons taking into account the electric and magnetic polarizabilities has been obtained.     

Wolf equations for two-photon light

The spatiotemporal two-photon probability amplitude that describes light in a two-photon entangled state obeys equations identical to the Wolf equations, which are satisfied by the mutual coherence function for light in any quantum state. Both functions therefore propagate similarly through optical systems. A generalized van Cittert-Zernike theorem explains the predicted enhancement in resolution for entangled-photon microscopy and quantum lithography. The Wolf equations provide a particularly powerful analytical tool for studying three-dimensional imaging and lithography since they describe propagation in continuous inhomogeneous media.     

Decoherence of Two-qubits Coupled with Reservoirs Studied with New Ket-Bra Entangled State Method

For the first time we define a so-called Ket-Bra Entangled State (KBES) for two-qubits coupled with reservoirs by introduce an extra fictitious mode vector, and convert the corresponding master equation into Schrödinger-like equation by virtue of this state. Via this approach we concisely obtain the dynamic evolution of two uncoupled qubits each immersed in local thermal noise. Based on this, the decoherence evolution for the extended Werner-like states is derived and how purity and temperature influence the concurrence is analyzed. This KBES method may also be applied to tackling master equations of limited atomic level systems.     

耗散Jaynes-Cummings模型中微观与唯象学主方程方法的比较

在有耗散的Jaynes-Cummings模型中,对原子与腔复合系统初始处于贝尔态或是原子激发态而腔场为真空态时分别运用微观与唯象学主方程进行求解,并分析这两类主方程在不同耦合区域的区别．结果显示,在强耦合和大失谐情况下,微观主方程求解得到的原子基态的布居数呈线性增长,但唯象学主方程获得的结果却呈非线性增加．在弱耦合区域,这两类主方程求解得到的原子基态布居数都出现快速增加,但是用唯象学主方程要比用微观主方程得到的布居数增加得更快．通过分析与讨论,该结果可能对耗散的腔QED中更好的实现逻辑门提供理论参考．     

On a simple derivation of master equations for diffusion processes driven by white noise and dichotomic Markov noise

A very simple way is presented of deriving the partial differential equations (the master equations) satisfied by the probability density for certain kinds of diffusion processes in one dimension, in which the driving term is a Gaussian white noise, or a dichotomic noise, or a combination of the two. The method involves the use of certain ‘formulas of differentiation’ to derive the equations obeyed by the characteristic functions of the processes concerned, and thence the corresponding master equations. The examples presented cover a substantial number of diffusion processes that occur in physical modelling, including some master equations derived recently in the literature for generalizations of persistent diffusion.     

Isomeric orientation by two-photon excitation: a theoretical study

I develop the theory of molecular orientation induced by two-photon isomerization. Phenomenologically, two-photon isomeric orientational hole burning and reorientation induce molecular orientation while rotational diffusion tends to randomize it. Using the formalism of Legendre polynomials solves the general equations of the theory, and analytical solutions are derived for actual physical cases at the early time evolution and the steady state of two-photon excitation. The theory explains the observed results of two-photon molecular orientation, and predicts additional experiments in this direction. The isomerization parameters and the movement of the isomers during polarized two-photon excitation can be quantified by the analytical theory. A theoretical study on the creation of molecular orientation by competing orientational Kerr effect and two-photon orientation is also presented.     

Variational master equation approach to dynamics of magnetic moments

Non-equilibrium properties of a model system comprised of a subsystem of magnetic moments strongly coupled to a selected Bose field mode and weakly coupled to a heat bath made of a plurality of Bose field modes was studied on the basis of non-equilibrium master equation approach combined with the approximating Hamiltonian method. A variational master equation derived within this approach is tractable numerically and can be readily used to derive a set of ordinary differential equations for various relevant physical variables belonging to the subsystem of magnetic moments. Upon further analysis of the thus obtained variational master equation, an influence of the macroscopic filling of the selected Bose field mode at low enough temperatures on the relaxation dynamics of magnetic moments was revealed.     

Two-photon lasers based on intersubband transitions in semiconductor quantum wells

We propose to make a two-photon laser based on intersubband (sublevel) transitions in semiconductor nanostructures. The advantages and feasibility of such a two-photon laser are analyzed in detail using the density matrix approach. Both one-photon and two-photon gains in a three subband quantum well structure are studied on the same footing to show how the two-photon gain can be maximized, while the competing one-photon gain is minimized. The results show that a sufficient two-photon gain can be achieved to overcome one-photon competition and the loss of a conventional semiconductor cavity, making intersubband transitions one of the very few feasible approaches to two-photon lasing.     

Emission of phonons by vortex filaments and the decay of a turbulent state in the Bose condensate

A turbulence decay mechanism in the Bose condensate (superfluid liquid) that is associated with the emission of acoustic waves upon reconnection of vortex filaments is studied. An approach based on the master equation for the length distribution of vortex loops is developed. Evolution equations for the density of the vortex filaments in the quasistationary and non-quasistationary regimes are derived. The decay law is compared to the numerical simulation results.