频率随时间变化的受迫谐振子的压缩态和压缩数态

研究了频率随时间变化的受迫谐振子系统的不变量和不变量的一般形式,并利用基本不变量构造了此含时系统的压缩态和压缩数态.     

Parametric oscillation with the cavity mode driven by coherent light and coupled to a squeezed vacuum reservoir

We seek to investigate, employing stochastic differential equations, the squeezing and statistical properties of the cavity mode of a degenerate parametric oscillator driven by coherent light and coupled to a squeezed vacuum reservoir. Contrary to the case of the squeezed vacuum reservoir, it is found that the driving coherent light has no effect on the squeezing properties of the cavity mode. However, both the squeezed vacuum reservoir and the driving coherent light increase the mean photon number of the cavity mode.     

Coherent states of a damped harmonic oscillator

We construct here the coherent states (annihilation operator eigenstates) of a damped harmonic oscillator. These coherent states, which are normalizable, have the desired behaviour in the classical limit (ℏ→0).     

动力学压缩真空中的Casimir力

利用Takahashi-Umea热场动力学方法研究了动力学压缩真空中的Casimir力,研究发现真空压缩与导体板间吸引力的存在互逆,随着时间演化(压缩度增大),原来的微弱吸引力将迅速转化为较强的排斥力.在板间温度以及压缩系数为零的特殊情形下,得到了与通常文献一致的结果.     

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.     

The geometric phase of a two-level atom in a narrow-bandwidth squeezed vacuum

In this paper, we derive the time dependent solution of the effective master equation for the reduced density matrix operator of a two level atom driven by a coherent laser field and damped by a finite bandwidth squeezed vacuum. The results show that the initial state setting, detuning parameter and Rabi frequency play important roles in the evolution of the system dynamics and geometric phase. We present a useful way for controlling the geometric phase variation for the system under consideration.     

Symmetries and conservation laws of the damped harmonic oscillator

We work with a formulation of Noether-symmetry analysis which uses the properties of infinitesimal point transformations in the space-time variables to establish the association between symmetries and conservation laws of a dynamical system. Here symmetries are expressed in the form of generators. We have studied the variational or Noether symmetries of the damped harmonic oscillator representing it by an explicitly time-dependent Lagrangian and found that a five-parameter group of transformations leaves the action integral invariant. Amongst the associated conserved quantities only two are found to be functionally independent. These two conserved quantities determine the solution of the problem and correspond to a two-parameter Abelian subgroup.      

Applications of the master equation of a two-level atom in a narrow-bandwidth squeezed vacuum

In this paper, we derive the time-dependent solution of the effective master equation for the reduced density matrix operator of a two-level atom driven by a coherent laser field and damped by a finite-bandwidth squeezed vacuum. The master equation has the standard form known from the broadband squeezing approaches but with new effective squeezing parameters and and new rate coefficients. There are also new terms, proportional to β, which are essentially narrow-bandwidth modifications determined by the parameters γ_n, δ_n and the shifts δ_N and δ_M. These parameters become zero when the squeezing bandwidth tends to infinity. The effects of the detuning parameter Δ of the driving laser field frequency ω_L from the atomic resonance ω_A and the squeezing parameters and on the atomic inversion, the von Neumann entropy and the resonance fluorescence spectrum are discussed.     

非旋波近似下压缩真空场与三能级原子依赖强度耦合系统的光场压缩

利用全量子理论,研究了非旋波近似下压缩真空场与V型三能级原子依赖强度耦合相互作用系统中光场的压缩效应.数值计算结果表明:光场呈现出周期性压缩现象,而虚光子过程则对光场的压缩具有抑制作用并产生量子噪声,量子噪声大小依赖于光场的初始压缩因子r和光场频率ω,且与原子-光场耦合强度g有关.随着r的增大,虚光子过程对光场压缩抑制作用程度由弱到强再由强到弱;随着ω和g的增大,量子噪声分别减小和增大.     

Quantum phases for a generalized harmonic oscillator

An effective Hamiltonian for the generalized harmonic oscillator is determined by using squeezed state wavefunctions. The equations of motion over an extended phase space are determined and then solved perturbatively for a specific choice of the oscillator parameters. These results are used to calculate the dynamic and geometric phases for the generalized oscillator with this choice of parameters.      

弱抽运下光学参量过程中压缩真空场的光子统计性质

在理论和实验上研究了光学参量振荡中产生的弱压缩真空场的光子统计行为. 弱压缩真空具有强烈的光子聚束效应,这种比热光场更强的聚束效应在量子光学和量子测量中具有重要的应用. 利用远离阈值的光学参量振荡(optical parametric oscillator, OPO )过程,在实验上产生了该弱压缩真空输出,运转波长在铯原子线附近. 通过Hanbury-Brown-Twiss(HBT)测量了OPO输出光场的二阶关联函数,实验结果与理论分析基本一致. 关键词： 压缩真空态 二阶相干度 光学参量振荡     

Quantum harmonic oscillator presented in a nonorthodox approach

An example of nonequivalent but s-equivalent Lagrange function for a one-dimensional harmonic oscillator are presented and discussed. The quantum approach displays a quite different structure from the usual standard one.     

Optical bistability of a composite system induced by a broadband squeezed vacuum

A composite system consisting of a degenerate optical parametric oscillator （DOPO） and N two-level atoms interacting with a broadband squeezed vacuum （SV） centred at frequency cas and an input monochromatic pumping field with a frequency ωp is analysed. The corresponding explicit analytical steady-state solutions in the central mode ωp = ωs are derived, and the result displays optical bistability （OB）. In addition, the influence of the broadband SV on the bistable behaviour is analysed in detail.     

压缩真空态中原子与场的量子纠缠和量子discord

在压缩真空库中,研究了原子与场的相互作用下二比特体系的量子discord和量子纠缠的动力学行为.重点分析了原子的初始态系数和压缩真空库的压缩系数对量子纠缠和量子discord的影响.通过数值分析我们得到,随着原子的初始态系数和压缩真空库的压缩系数值的增加,量子纠缠和量子discord都会减小,但量子纠缠比量子discord减小的更快一些.最后研究了在原子的初始态系数和压缩真空库的压缩系数的值相同的情况下,量子discord比量子纠缠存在的时间更长些.     

Preservation of coherence for a two-level atom tunneling through a squeezed vacuum with finite bandwidth

Tunneling of a two-state particle through a squeezed vacuum is considered. It has been shown that repetitive measurement or interaction with the external field can preserve the coherence. Moreover, the coherence time in terms of the squeezing parameters has been calculated. A specific condition is derived, under which the coherence is sustainable.     

受与速度平方成正比的力的变频率谐振子

受与速度平方成正比的力的变频率谐振子(THOFQV)可以用一个适当的Lagrangian量来描述，可以求出THOFQV的普遍解.再利用不变量算子求解该系统的Schrdinger方程，得到本征函数和本征值. 关键词： 谐振子 不变量 本征函数 本征值     

Kerr介质中压缩真空场与耦合双原子依赖强度耦合系统原子布居数的时间演化

研究了存在Kerr介质时,单模压缩真空场与耦合双原子依赖强度耦合相互作用系统原子布居数的时间演化规律,讨论了Kerr介质、原子间相互作用和光场的初始压缩因子对原子布居数时间演化的影响.     

过阻尼谐振子的随机共振

研究了由交叉相关高斯白噪声驱动的过阻尼谐振子的随机共振,其中加法噪声被周期信号所调制,运用平稳关联函数的傅里叶变换,导出了过阻尼谐振子随机模型信噪比的精确表达式.结果揭示:在过阻尼谐振子的随机模型中存在二类随机共振.一类随机共振表现为信噪比随乘法噪声强度Q变化的曲线存在共振峰,另一类随机共振表现为信噪比随振子频率ω变化的曲线存在共振峰.大幅度改变信号频率Ω值的大小,信噪比随乘法噪声强度Q变化的曲线有单峰,一峰一谷和单调变化三种不同的形式.     

受到与速度平方成正比的力的谐振子的普遍解

将Ermakov系统加以推广，得出受到与速度平方成正比的力的变频率谐振子的不变量，求出其普遍解．     

Coherent states of general time-dependent harmonic oscillator

By introducing an invariant operator, we obtain exact wave functions for a general time-dependent quadratic harmonic oscillator. The coherent states, both inx- andp-spaces, are calculated. We confirm that the uncertainty product in coherent state is always larger thankh/2 and is equal to the minimum of the uncertainty product of the number states. The displaced wave packet for Caldirola-Kanai oscillator in coherent state oscillates back and forth with time about the center as for a classical oscillator. The amplitude of oscillation with no driving force decreases due to the dissipation in the system. However, the oscillation with resonant frequency oscillates with a large amplitude, even after a sufficient time elapse.