Entanglement Between Two Dipole-Coupled Qubits Interacting with Two Independent Slightly Detuned Cavity Modes

Considering the generalized double Jaynes-Cummings model, we examine the entanglement between two non-identical dipole-dipole coupled qubits interacting with two independent detuned vacuum cavity modes. We calculate the negativity as a measure of qubits entanglement. We find that entanglement parameter evolve periodically with time and the period are affected by the model parameters and initial states of qubits. For unentangled initial states the detuning and dipole-dipole interaction affect only the period of entanglement oscillations, not the maximum value of entanglement. For entangled states the detuning stabilizes the entanglement parameter oscillations. According to choice of initial entangled state the dipole-dipole strength is greatly enhances or weakens the oscillations of the entanglement parameter.

     

Preparation and control of entangled states in the two-mode coherent fields interacting with a moving atom via two-photon process

We investigate the preparation and the control of entangled states in a system with the two-mode coherent fields interacting with a moving two-level atom via the two-photon transition. We discuss entanglement properties between the two-mode coherent fields and a moving two-level atom by using the quantum reduced entropy, and those between the two-mode coherent fields by using the quantum relative entropy. In addition, we examine the influences of the atomic motion and field-mode structure parameter $p$ on the quantum entanglement of the system. Our results show that the period and the duration of the prepared maximal atom-field entangled states and the frequency of maximal two-mode field entangled states can be controlled, and that a sustained entangled state of the two-mode field, which is independent of atomic motion and the evolution time, can be obtained, by choosing appropriately the parameters of atomic motion, field-mode structure, initial state and interaction time of the system.     

Entanglement Dynamics in a Model Tripartite Quantum System

A Λ-type atom interacting with two radiation fields exhibits electromagnetically induced transparency and other nonclassical effects that appear in the entanglement dynamics of the atomic subsystem and in appropriate field observables. Both EIT and field-atom entanglement are important for quantum information processing. We investigate the roles played by specific initial field states, detuning parameters, field nonlinearities and intensity-dependent field-atom couplings on EIT and the entanglement between subsystems. Departure from coherence of the initial field states produces significant effects. We investigate these aspects in a model that exhibits the salient features of entangled tripartite systems. For initial photon-added coherent states, collapses and revivals of the atomic subsystem von Neumann entropy appear as the intensity parameter varies over a narrow range of values. These features could be useful in enabling entanglement.     

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。     

Control and Transfer of Entanglement between Two Atoms Driven by Classical Fields under Dressed-State Representation

We have studied the dynamics and transfer of the entanglement of the two identical atoms simultaneously interacting with vacuum field by employing the dressed-state representation. The two atoms are driven by classical fields. The influence of the initial entanglement degree of two atoms, the coupling strength between the atom and the classical field and the detuning between the atomic transition frequency and the frequency of classical field on the entanglement and atomic linear entropy is discussed. The initial entanglement of the two atoms can be transferred into the entanglement between the atom and cavity field when the dissipation is neglected. The maximally entangled state between the atoms and cavity field can be obtained under some certain conditions. The time of disentanglement of two atoms can be controlled and manipulated by adjusting the detuning and classical driving fields. Moreover, the larger the cavity decay rate is, the more quickly the entanglement of the two atoms decays.     

A novel scheme of hybrid entanglement swapping and teleportation using cavity QED in the small and large detuning regimes and quasi-Bell state measurement method

We outline a scheme for entanglement swapping based on cavity QED as well as quasi-Bell state measurement(quasiBSM) methods. The atom–field interaction in the cavity QED method is performed in small and large detuning regimes.We assume two atoms are initially entangled together and, distinctly two cavities are prepared in an entangled coherent–coherent state. In this scheme, we want to transform entanglement to the atom-field system. It is observed that, the fidelities of the swapped entangled state in the quasi-BSM method can be compatible with those obtained in the small and large detuning regimes in the cavity QED method(the condition of this compatibility will be discussed). In addition, in the large detuning regime, the swapped entangled state is obtained by detecting and quasi-BSM approaches. In the continuation,by making use of the atom–field entangled state obtained in both approaches in a large detuning regime, we show that the atomic as well as field states teleportation with complete fidelity can be achieved.     

双模纠缠相干光场与V型三能级原子相互作用系统的光子统计性质

本文采用求解Schrodinger方程和数值计算方法,研究了双模纠缠相干光场与三能级原子相互作用系统的光子统计性质,结果表明:此性质与双模纠缠相干光场的纠缠程度、失谐量、双模光的平均光子数和原子的初态相关联.     

Generating controllable atom-light entanglement with a Raman atom laser system

We introduce a scheme for creating continuous variable entanglement between an atomic beam and an optical field, by using squeezed light to outcouple atoms from a Bose-Einstein condensate via a Raman transition. We model the full multimode dynamics of the atom laser beam and the squeezed optical field and show that, with appropriate two-photon detuning and two-photon Rabi frequency, the transmitted light is entangled in amplitude and phase with the outcoupled atom laser beam. The degree of entanglement is controllable via changes in the two-photon Rabi frequency of the outcoupling process.     

Different entanglement dynamics and transfer behaviors due to dipole-dipole interaction

We analyze entanglement dynamics and transfer in a system composed of two initially correlated two-level atoms, in which each atom is coupled with another atom interacting with its own reservoir. Considering atomic dipole-dipole interactions, the results show that dipole-dipole interactions restrain the entanglement birth of the reservoirs, and a parametric region of dipole-dipole interaction strength exists in which the maximal entanglement of two initially uncorrelated atoms is reduced. The transfer of entanglement shows obvious different behaviors in two initial Bell-like states.     

Entanglement and Pancharatnam Phase for Two Two-Level Atoms Interacting with a Single Mode Field

A model of two 2-level atoms interacts with a single quantized electromagnetic field is considered. We study the effect of the mean photon number and the structure of the initial states of the two atoms on the dynamics of the atomic system from the separability point of view. It is found that, if we start from a product mixed atomic state, the probability of generating long living entangled states is increased as the mean photon number increases. Starting from excited atomic system in product state, one generates a more stable entangled states with high degree of entanglement. Also, the effect of the mean photon number on atomic system prepared initially in entangled states is investigated. It is found that the entangled state generated from the initially partial entangled states are more robust than those obtained from a maximum entangled state. The Pancharatnam phase for the separable and entangled states is studied under the effect of the mean photon number and the structure of the initial state. We find that for the separable states, the collapses decrease and the amplitude of the revivals is smaller than that for the entangled state, so there are long-living entangled phases. This property give us a great chances to store safely information in entangled state.     

Dynamics of Entanglement between Moving Four-Level Atom and Single Mode Cavity Field

In this paper we are interested in studying the entanglement between a single four-level ladder-type atom interacting with one-mode cavity field when the atomic motion is taken into account. The exact solution of the model is obtained by using Schrodinger equation for a specific initial conditions. The field entropy of this system is investigated in the non-resonant case. The effects of the detuning parameter and the atomic motion on the entanglement degree are examined. These investigations show that both of the detuning and the atomic motion play important roles in the evolution of the von Neumann entropy and atomic populations. Finally, conclusions and some features are given.     

双模纠缠相干光场与V型三能级原子相互作用系统的原子偶极压缩效应

采用求解Schroedinger方程和数值计算方法，研究了双模纠缠相干光场与V型三能级原子相互作用过程中原子偶极算符的压缩效应，结果表明：此压缩效应与双模纠缠光场的纠缠程度、失谐量相关联。     

The influences of dipole--dipole interaction and detuning on the sudden death of entanglement between two atoms in the Tavis--Cummings model

The influences of dipole--dipole interaction and detuning on the entanglement between two atoms with different initial tripartite entangled W-like states in the Tavis--Cummings model have been investigated by means of Wootters' concurrence, respectively. The results show that the entanglement between the two atoms can be enhanced via appropriately tuning the strength of dipole--dipole interaction of two atoms or the detunings between atom and cavity, and the so-called sudden death effect can be weakened simultaneously.     

Entanglement swapping in two independent Jaynes-Cummings models

We consider two independent Jaynes-Cummings models which consist of an atom interacts with electromagnetic field modes. The generation of atom-atom entanglement is investigated. No direct interaction between the two atoms exists. Entanglement can be created using entanglement swapping method by an interference measurement performed on photons. We discuss the influence of off-resonance and the initial state of the atom on the atom-atom entanglement. It is shown that the maximal atom-atom entanglement can be obtained and the atom-atom entanglement is sensitive to the off-resonance and the initial state of the atom.     

共振和非共振情况下非简并双光子Tavis-Cummings模型中原子与原子之间的纠缠演化

针对共振和非共振情况讨论了非简并双光子Tavis-Cummings(T-C)模型中原子与原子之间的纠缠演化,得到纠缠度的解析表达式.基于两类型不同的初态,详细分析了光场本征频率、原子跃迁频率以及原子与原子间偶极相互作用对纠缠的影响,并比较了共振和非共振情况下的纠缠演化行为.     

双模纠缠相干光场与Ⅴ型三能级原子相互作用系统的原子偶极压缩效应

采用求解Schrodinger方程和数值计算方法,研究了双模纠缠相干光场与Ⅴ型三能级原子相互作用过程中原子偶极算符的压缩效应,结果表明:此压缩效应与双模纠缠光场的纠缠程度、失谐量相关联.     

Entanglement dynamics of qubits in a common environment

We use the quantum jump approach to study the entanglement dynamics of a quantum register, which is composed of two or three dipole-dipole coupled two-level atoms, interacting with a common environment. Our investigation of entanglement dynamics reflects that the environment has dual actions on the entanglement of the qubits in the model. While the environment destroys the entanglement induced by the coherent dipole-dipole interactions, it can produce stable entanglement between the qubits prepared initially in a separable state. The analysis shows that it is the entangled decoherence-free states contained as components in the initial state that contribute to the stable entanglement. Our study indicates how the environmental noise produces the entanglement and exposes the interplay of environmental noise and coherent interactions of qubits on the entanglement.     

Entanglement for a Bimodal Cavity Field Interacting with a Two-Level Atom

Negativity has been adopted to investigate the entanglement in a system composed of a two-level atom and a two-mode cavity field. Effects of Kerr-like medium and the number of photon inside the cavity on the entanglement are studied. Our results show that atomic initial state must be superposed, so that the two cavityfield modes can be entangled. Moreover, we also conclude that the number of photon in the two cavity mode should be equal. The interaction between modes, namely, the Kerr effect, has a significant negative contribution. Note that the atom frequency and the cavity frequency have an indistinguishable effect, so a corresponding approximation has been made in this article. These results may be useful for quantum information in optics systems.     

两二能级原子在共同环境下的量子关联动力学

通过精确求解带有偶极-偶极相互作用的两个二能级原子与一个共同热库相互作用模型, 得到了两原子间量子纠缠和量子失谐(quantum discord)的解析表达式. 综合考虑了环境的非马尔可夫效应、原子间的偶极-偶极相互作用以及原子的本征频率同腔模中心频率之间的失谐量对两原子间量子纠缠和quantum discord的影响. 研究显示: 在非马尔可夫机制下, 且原子的本征频率与腔模中心频率是共振时, 当两原子初态处于纠缠态时, 原子间偶极-偶极相互作用可以显著抑制包括量子纠缠和quantum discord等量子关联的衰减, 更特别的是, 如果原子的本征频率同腔模中心频率有一定的失谐时, 利用原子间偶极-偶极相互作用可大大地延长两原子退纠缠的时间; 当两原子初态处于可分离态时, 从短时间来看, 原子间偶极-偶极相互作用可以提高量子纠缠和quantum discord振荡的振幅,而在长时间极限下, 原子间偶极-偶极相互作用不会改变量子纠缠和quantum discord达到的稳定值. 最后, 讨论了原子间偶极-偶极相互作用对量子纠缠和quantum discord动力学不同的影响. 关键词： 量子纠缠 量子失谐 共同环境 偶极-偶极相互作用     

内禀退相干下Tavis-Cummings模型中原子的纠缠演化与贝尔不等式破坏

通过求解系统的Milburn方程，研究了两个二能级原子和单模场相互作用系统中原子间纠缠和贝尔不等式破坏随时间的演化特性，讨论了偶极相互作用、场与原子的失谐量对纠缠度以及贝尔不等式破坏的影响.结果表明：原子间偶极-偶极相互作用对纠缠度和贝尔不等式破坏有显著影响，失谐量增大会使两原子的纠缠度和贝尔不等式破坏变大，并且两原子所能达到稳定的纠缠受偶极相互作用系数与失谐量两者之差的影响.同时还发现两原子的纠缠与贝尔不等式破坏并不是单调的函数关系，很小的纠缠也可以产生贝尔不等式破坏. 关键词： Milburn理论 偶极-偶极相互作用 失谐量 贝尔不等式破坏