Quantum Mechanics of Two-Field Parametric Frequency Converter Interacting with a Single Atom

In this communication we deal with a new model Hamiltonian representing the interaction between a two-level atom and two electromagnetic field modes in a cavity. The interaction between the modes has been taken into account and considered to be of a parametric frequency converter type. The model can be regarded as a generalization of two different systems: the Jaynes–Cummings model (atom–field interaction) and the two-mode frequency converter model (field–field interaction). Under a certain condition an exact solution for the equations of motion in the Heisenberg picture is given. The wavefunction in the Schrödinger picture is also constructed and used to discuss some statistical properties related to the model. We assume that the fields are initially in coherent states. We discuss atomic inversion, photon number distribution, squeezing and other phenomena. We show in all cases that the system is very sensitive to any variation in the mean photon numbers.     

Influence of the virtual photon field on the squeezing properties of atom laser

This paper investigates the squeezing properties of an atom laser without rotating-wave approximation in the system of a binomial states field interacting with a two-level atomic Bose--Einstein condensate. It discusses the influences of atomic eigenfrequency, the interaction intensity between the optical field and atoms,parameter of the binomial states field and virtual photon field on the squeezing properties. The results show that two quadrature components of an atom laser can be squeezed periodically. The duration and the degree of squeezing an atom laser have something to do with the atomic eigenfrequency and the parameter of the binomial states field, respectively. The collapse and revival frequency of atom laser fluctuation depends on the interaction intensity between the optical field and atoms. The effect of the virtual photon field deepens the depth of squeezing an atom laser.     

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.     

双参数形变谐振子奇偶相干态的高阶压缩特性

研究了双参数qs形变谐振子奇偶相干态中光场的高阶压缩特性,并用数值计算方法定量研究了形变参数q和s对这一特性的影响规律.结果表明,qs形变谐振子奇偶相干态均可能呈现奇次方阶压缩效应却无偶次方阶压缩效应,这与谐振子没有形变时的通常情况是不同的.当q和s取一定值时,在qs形变相干态中谐振子强度r²取值的一定范围内,这种反常特性的范围随着q偏离1越大s取值越小而变大.有关单参数q形变奇偶相干态的结论作为特例包含在本文的一般结论之中.     

Damping in the Interaction of a Field and Two Three-Level Atoms Through Quantized Caldirola–Kanai Hamiltonian

We investigate the damped interaction between two Λ-type three-level atoms and a quantized single-mode cavity field, for which the Hamiltonian of the field is rewritten in Caldirola–Kanai form. We obtain the wave functions for the case where the two atoms are initially prepared in arbitrary pure states and the field is initially prepared in the coherent state. We investigate numerically the influence of the damping parameter on the temporal behavior of the Mandel Q-parameter, linear entropy, and normal squeezing. We find the damping parameter and initial atomic states to play central roles in the nonclassical features and the degree of entanglement.     

双光子Jaynes-Cummings模型中初始原子相干性对辐射场压缩的影响

本文研究了任意初态的双光子Jaynes-Cummings模型的一般演化规律,着重于分析初始原子相干性对辐射场压缩行为的影响,作为例子,讨论了一个任意初态的二能级原子与真空态和相干态光场相互作用时辐射场的压缩.数值计算了各种条件下辐射场压缩的时间演化.     

双光子Jaynes—Cummings模型中初始原子相干性对辐射场...

本文研究了任意初态的双光子Jaynes-Cummings模型的一般演化规律,着重于分析初始原子相干性对辐射场压缩行为的影响,作为例子,讨论了一个任意初态的二能级原子与真空态和相干态光场相互作用时辐射场的压缩.数值计算了各种条件下辐射场压缩的时间演化.     

虚光场对玻色-爱因斯坦凝聚体与二项式光场相互作用系统中光场压缩性质的影响

在二项式光场和二能级原子玻色-爱因斯坦凝聚体相互作用系统中, 应用全量子理论, 分别在旋波近似和非旋波近似下, 研究了光场的压缩特性以及原子本征频率、原子-光场的耦合系数、光场参数以及虚光场对系统光场压缩特性的影响. 研究表明, 光场的两个正交分量均被周期性压缩, 光场压缩持续时间与原子的本征频率有关, 压缩深度与二项式光场概率分布参数和虚光场有关, 光场与原子的耦合系数决定了光场涨落的崩塌-回复频率. 关键词： 量子光学 玻色-爱因斯坦凝聚 虚光场 光场压缩     

V型三能级原子与非经典光场作用中光场特性的变化

研究了V型三能级原子BEC与双模压缩光场相互作用系统中,忽略原子间相互作用和考虑原子间相互作用时光场的正交压缩和光子数压缩。结果表明,光场的正交压缩依赖于压缩参数,而光子数压缩与压缩参数、光场信号强度有关,在一定条件下,两种压缩可同时存在。原子间相互作用影响两种压缩的涨落随时间变化的周期,以及正交分量涨落随时间变化的幅度,而对光子数压缩涨落随时间变化的幅度几乎无影响。     

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     

Spin Squeezing and Quantum Fisher Information in Generalized Two-Axis Twisting Model

We investigated spin squeezing and quantum Fisher information in generalized two-axis twisting model; which generalizes the two-axis twisting model including a linear interaction controlled by an external field. In particular, we are interested in the dependence of spin squeezing and quantum Fisher information on the external field. By adopting frozen-spin approximation, we derive the theoretical and numerical results for spin squeezing and quantum Fisher information. Except certain special conditions, the stronger external field induces to stronger squeezing. Spin squeezing parameter and the reciprocal of the mean quantum Fisher information per particle are periodic function; but the external field has not important effect on the period.     

Kerr介质中耦合V型三能级原子与相干态光场作用场的量子性质

研究了Kerr介质中相干态光场与耦合V型三能级原子相互作用过程中场的量子性质.利用量子光学中光场与原子相互作用的耦合Tavis-Cummings模型,对系统的动力学过程进行了求解.讨论了系统初始状态、失谐量、原子间偶极相互作用强度及Kerr系数对光场量子性质随时间演化的影响.数值计算结果表明:初态中场的平均光子数比较小时,光场能够展现出明显的量子效应|初始时刻原子激发态概率幅从小变大时,光场的反聚束效应变得越明显,而光场的压缩深度会先增大后减小|失谐量的变化对场的量子性质的影响不大,只是改变光场二阶相关函数和压缩参量振荡的周期|原子间耦合强度的增大使光场的反聚束效应减弱和光场的压缩深度变浅|Kerr系数的增大会增强光场的反聚束效应,而使光场的压缩深度变浅.     

V型三能级原子双模光场系统中光场压缩性质

本文利用格子液体方法对文献中给出的V型三能级原子玻色-爱因斯坦凝聚体与双模压缩相干态光场相互作用系统的哈密顿量进行分析,发现文献中对原子间相互作用部分的处理有不合理之处,从而对该哈密顿量作出了改进并研究了V型三能级原子双模光场系统中光场压缩性质.结果表明:光场两正交分量交替呈现周期性压缩现象,其压缩深度与光场初始压缩因子密切相关,而压缩时间与双模光场的频率有关. 关键词： 玻色-爱因斯坦凝聚 V型三能级原子 压缩相干态 双模压缩态光场     

Quantum entanglement and nonlocality properties of two-mode Gaussian squeezed states

Quantum entanglement and nonlocality properties of a family of two-mode Gaussian pure states have been investigated. The results show that the entanglement of these states is determined by both the two-mode squeezing parameter and the difference of the two single-mode squeezing parameters. For the same two-mode squeezing parameter, these states show larger entanglement than the usual two-mode squeezed vacuum state. The violation of Bell inequality depends strongly on all the squeezing parameters of these states and disappears completely in the limit of large squeezing. In particular, these states can exhibit much stronger violation of local realism than two-mode squeezed vacuum state in the range of experimentally available squeezing values.     

Preparation and control of atomic optimal entropy squeezing states for a moving two-level atom under control of the two-mode squeezing vacuum fields

From the viewpoint of quantum information,this paper studies preparation and control of atomic optimal entropy squeezing states(AOESS) for a moving two-level atom under control of the two-mode squeezing vacuum fields.Necessary conditions of preparation of the AOESS are analysed,and numerical verification of the AOESS is finished.It shows that the AOESS can be prepared by controlling the time of the atom interaction with the field,cutting the entanglement between the atom and field,and adjusting squeezing factor of the field.An atomic optimal entropy squeezing sudden generation in different components can alternately be realized by controlling the field-mode structure parameter.     

Atom–field interaction under the influence of two external classical and quantum fields

In this paper we introduce a new version of the interaction between a two-level atom and an external electric field in the presence of the classical field. Under a certain condition the system is transformed to the usual Jaynes–Cummings model. The atomic inversion is investigated where the phenomenon of super-structure is reported for a large value of the classical field coupling parameter. Assuming that the field is initially in the displaced thermal state the variance and the entropy squeezing as well as the degree of entanglement are discussed. Our results show that the information of variance and entropy squeezing beside the purity can be controlled by both of the coupling parameter of the classical field and the mean photon number. In this context the variance and the entropy squeezing become more pronounced for large values of the classical field coupling, while the system shows period of disentanglement during the considered time.     

量子混沌系统中的自旋压缩性质

量子信息是21世纪的一门新兴交叉学科,现已经成为世界关注的热门研究领域.近年来,量子计算机的研究正成为大家十分感兴趣的课题.在寻找量子计算的实现方案过程中,量子混沌引起了研究人员的极大关注,因为在量子计算机执行一些量子运算法则的过程中可能产生量子混沌,并可能破坏量子计算机的运算操作条件.近期有关量子纠缠与量子混沌之间的关系已经有所报道,而自旋压缩作为另外一种典型的纯量子效应,是否也与量子混沌之间存在一定关系呢?讨论了量子混沌研究中一个非常典型的QKT模型,研究了量子混沌系统中自旋压缩的性质.通过数值模拟计算,给出了两种不同定义的自旋压缩系数与混沌系数κ之间的变化关系,结果发现在经典相空间中,如果在规则区域占优势的情况下,当初始自旋相干态波包位于椭圆形中心时,随着时间的演化,系统压缩行为表现得非常强;而对于经典相空间中混沌区域占优势的情况下,初始自旋相干态波包同样位于椭圆形中心,则系统的压缩行为表现得非常弱,说明自旋压缩对相应的经典混沌非常敏感.通过比较还发现,采用Wineland等定义的自旋压缩系数比采用Kitagawa和Ueda等定义的自旋压缩系数对经典混沌更敏感一些,从而得出用自旋压缩可以刻画量子混沌的结论.     

Creating unconventional geometric phase gate using squeeze-like operator assisted by strong driving field

Based on the idea that a squeezing process can be thought of as a total cumulative effect of a large number of tiny squeezing processes, we define a squeeze-like operator with a time-dependent squeeze parameter. Applying this operator to and combining with a system which includes a two-photon interaction between two atoms and an initial vacuum cavity field, and resorting to a resonant strong driving classical field, we obtain an unconventional geometric phase gate with a shorter gating time.     

Spin Squeezing of a General 3-Qubit State

We investigate the spin squeezing of a general 3-qubit state, which is superposed by a GHZ state and two W states. Numerical solutions for the length of mean spin, mean spin direction and spin squeezing were given. It is shown that the mean spin direction, the length of mean spin and the spin squeezing parameter are determined by the superposition coefficients and the relative phases between the GHZ state and the two W states.     

Spin Squeezing of 4-Qubit State

We investigate the spin squeezing of a 4-qubit state, which is superposed by a 4-qubit GHZ state and two W states with a relative phase. Numerically solution for spin squeezing parameter is given. It is shown that the parameter depends on the superposition coefficients and the relative phase. It is shown that spin squeezing exists over a relatively long time with increasing superposition coefficient γ and the smaller the value of relative phase is, the longer the time of existing spin squeezing.