Kerr介质中耦合双原子的纠缠特性

研究了Kerr介质中两个耦合二能级原子的纠缠演化规律, 通过concurrence计算了系统的纠缠度, 讨论了系统初态、Kerr 介质和原子之间的偶极相互作用对腔中两个原子纠缠度的影响. 结果表明: 通过适当选取Kerr介质的耦合系数和偶极相互作用强度, 可以获得固定的两原子纠缠, 并且可以提高两原子之间的纠缠, 甚至彻底消除纠缠猝死现象. 关键词： 偶极相互作用 Kerr介质 concurrence     

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     

非旋波近似下两纠缠原子的纠缠特性

采用了相干态正交化法研究了耦合强度以及偶极相互作用对Tavis-Cummings模型中两原子的纠缠的影响.与旋波近似比较发现,在弱耦合强度下,非旋波近似下两原子间的纠缠与旋波近似下的结果符合得很好,在强耦合区,原子之间的纠缠出现了突然死亡现象.研究同时发现耦合强度越大,原子间处于可分离态的时间越长,表明了原子间处于退纠缠的时间的长短是依赖于原子-光场的耦合强度的.而考虑了偶极相互作用时,随着偶极-偶极相互作用的加强,原子间的纠缠也将被加强.     

Entanglement generation in trapped atoms

The two atoms in the ion trap are entangled by the interaction with an external excited atom. The evolution of the entanglement is analytically derived without the decoherence. Considering the spontaneous decay from the environment, the evolution of the entanglement is similar to the damping Rabi oscillation. The generation of entanglement is induced by the dipole-dipole type interaction of atoms. It is found that the entanglement of two trapped atoms is robust with the uniform interaction with the external atom. The collective spontaneous emission from the coupling between the atoms may enhance the entanglement.     

The Effect of Dipole-Dipole Interaction on Tripartite Entanglement in Different Cavities

The effect of dipole-dipole interaction, the initial relative phase and the coupling strength with the cavity on the dynamics of three two level atoms in the good and the bad cavity regime are investigated. It is found that the presence of strong dipole-dipole interaction not only ensures avoiding entanglement sudden death but also retains entanglement for long time. The choice of the phase in the initial state is crucial to the operational regime of the cavity. Under specific conditions, the entanglement can be frozen in time to its initial values through strong dipole-dipole interaction. This trait of tripartite entanglement may prove helpful in engineering multiparticle entanglement for the practical realization of quantum technology.     

双模纠缠相干光与Bell态原子系统的光子统计

运用全量子理论并结合数值计算方法,研究了处于Bell态的两个全同二能级纠缠原子与双模纠缠相干光场相互作用系统的光子统计性质.分析了双原子体系的初态、光场的平均光子数、双模纠缠相干光场的纠缠程度以及双原子体系的原子间耦合强度对双模光场的光子统计性质的影响.结果表明：双原子体系的初态为｜β00〉、｜β10〉时,光场在其演化过程中不出现光子的反聚束效应；而当原子初态为｜β01〉或｜β11〉时,在一定的条件下可出现光子的反聚束效应.并且在光场的演化过程中,光子的反聚束效应出现的次数、时间和深度极其敏感地依赖于初始光场的平均光子数,而受到双模纠缠光场的纠缠程度以及双原子间偶极作用强度的影响很微弱.     

Coherent control of quantum correlations in atomic systems

A new mechanism of development of quantum correlations due to the combined effects of a common heat bath and a resonant classical electromagnetic field is analyzed for a system of two two-level atoms coupled by dipole-dipole interaction. Conditions are found under which arbitrary steady-state entanglement can be created in the absence of measurement in an entangled basis. The analysis of dynamics of entanglement is focused on the effects of dipole-dipole interaction, mean number of thermal photons, degree of squeezing of thermal radiation, classical field strength, and presence of additional decay channels.     

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     

Creation of quantum correlations via the initial classical-mixed states

Using the pseudomode method, we theoretically analyze the creation of quantum correlations between two two-level dipole-dipole interacting atoms coupled with a common structured reservoir with different coupling strengths. Considering certain classes of initial separable-mixed states, we demonstrate that the sudden birth of atomic entanglement as well as the generation of stationary quantum correlations occur. Our results also suggest a possible way to control the occurrence time of entanglement sudden birth and the stationary value of quantum correlations by modifying the initial conditions of states, the dipole-dipole interaction, and the relative coupling strength. These results are helpful for the experimental engineering of entanglement and quantum correlations.     

控制Tavis-Cummings模型中两原子X态的纠缠突然死亡与突然产生

研究了初态为X态时Tavis-Cummings模型中具有偶极相互作用两原子的纠缠演化特性,在演化过程中,同时号码出现了两原子的纠缠突然死亡(ESD)与突然产生(ESB)两种有趣的现象.详细分析了两原子初始态的纯度、偶极相互作用、光场粒子数对这两种现象出现时间的影响,进一步给出了初始为混态时ESB与ESD的转换条件.计算结果表明,上述系统参量对两原子的纠缠演化、ESB与ESD有重要的影响,偶极相互作用会改变纠缠度的振荡周期,使出现ESD的时间间隔减少;随着初始两原子纠缠纯度的增大,纠缠突然产生以及纠缠突然死亡存在的时间缩短,并且可以提高两原子之间的纠缠;对于特殊的初态,产生了纠缠不变性以及固定的两原子纠缠,该定值受两原子初始状态的纯度控制。     

Tunable entanglement sudden death and three-partite entanglement in Tavis-Cummings model with an added nonlinear kerr-like medium

We investigate the entanglement dynamics and the phenomenon of entanglement sudden death in the two-photon Tavis-Cummings model with an added nonlinear kerr-like medium. It is shown that the phenomenon of entanglement sudden death can be controlled by the nonlinear kerr-like medium. Furthermore, the influence of dipole-dipole interaction on entanglement between atoms is also discussed. It is found that the phenomenon of entanglement sudden death can be weakened by the dipole-dipole interaction. Finally, we investigate the influence of kerr medium and dipole-dipole interaction on the three-partite entanglement of the system by making use of the state preparation fidelity.     

推广的Jaynes-Cummings模型中原子纠缠的时间演化和热纠缠态

利用共生纠缠度研究了一个推广Jaynes Cummings模型中两原子纠缠的时间演化和有限温度下系统热纠缠态. 结果表明，腔场中两原子展现出周期性的纠缠演化过程，演化周期随原子偶极 偶极相互作用强度的增大而减小；在有限温度下，系统的共生纠缠度随温度的升高而降低，当趋近临界温度时，系统纠缠现象消失，这一临界温度值与原子偶极-偶极相互作用强度成正比. 对于典型的实验数据，临界温度约在10-5K数量级. 此外，在这种Jaynes Cummings模型中存在量子相位转变. 关键词： Jaynes Cummings模型 原子纠缠态 热纠缠态 共生纠缠度 偶极 偶极相互作用     

压缩真空场与耦合双原子Raman相互作用系统场熵的演化特性

利用全量子理论,研究了压缩真空场与耦合双原子Raman相互作用系统的场熵演化特性,讨论了系统耦合常数和光场初始压缩因子对场熵演化特性的影响.结果表明,场熵的时间演化规律与原子布居差的时间演化规律非常相似.当原子间的偶极-偶极相互作用较弱时,场熵演化呈现周期性的崩塌与回复现象;当原子间的偶极-偶极相互作用较强时,场熵演化呈现不规则振荡,崩塌与回复周期现象消失.     

Entropy evolution properties in a system of two entangled atoms interacting with light field

In this paper, we use the field entropy as a measurement of the degree of entanglement between the light field and the atoms of the system which is composed of two dipole—dipole interacting two-level atoms initially in an entangled state interacting with the single mode coherent field in a Kerr medium. The influence of the coupling constant of dipole—dipole interaction between atoms and the coupling strength of the Kerr medium with the light field and the intensity of the light field on the field entropy are discussed by numerical calculations. It is shown that when the coupling strength of the Kerr medium with the light field is large enough, and the light field is strong, the degree of entanglement between the atoms with the light field becomes weaker. The degree of entanglement only changes slightly with the change of the coupling constant of dipole—dipole interaction between atoms.     

腔量子电动力学系统中耦合三原子的纠缠特性

研究了三个全同二能级原子与单模腔相互作用系统中原子间的三体纠缠特性.考虑原子间存在相互耦合,并且腔场处于弱相干态的情况,通过数值计算给出了纠缠量的演化曲线,讨论了原子间耦合强度和弱相干场强度对三体纠缠的影响.研究结果表明:随弱相干场强度增强,原子间的三体纠缠增强;相反,随原子间耦合系数增大,原子间三体纠缠减弱.     

Dynamical creation of entanglement versus disentanglement in a system of three-level atoms with vacuum-induced coherences

The dynamics of entanglement between three-level atoms coupled to the common vacuum is investigated. We show that the collective effects such as collective damping, dipole-dipole interaction and the cross coupling between orthogonal dipoles, play a crucial role in the process of creation of entanglement. In particular, the additional cross coupling enhances the production of entanglement. For the specific initial states we find that the effect of delayed sudden birth of entanglement, recently invented by Ficek and Tana? [Ficek, R. Tana?, Phys. Rev. A 77 (2008) 054301] in the case of two-level atoms, can also be observed in the system. When the initial state is entangled, the process of spontaneous emission causes destruction of correlations and its disentanglement. We show that the robustness of initial entanglement against the noise can be changed by local operations performed on the state.     

双模腔场中纠缠转移时纠缠与能量关系的研究

在初态为Bell态的两个二能级原子与双模腔场的耦合系统中,我们研究了其子系统纠缠转移时两原子的能量与其纠缠演化之间的关系。结果表明：两者的关系是密不可分的。而且,我们还讨论了原子间的偶极-偶极相互作用和腔场中的光子数对这种关系的影响。     

Critical properties of entanglement in the Dicke model with the dipole-dipole interactions

In this paper, we investigate two aspects of entanglement properties of the ground state for the Dicke model with the dipole-dipole interaction between the atoms in the thermodynamic limit, and observe how they are affected by the quantum phase transition. The appearance of dipole-dipole interactions between the atoms does not change the maximum atom-field entanglement at the critical point, while it changes the maximum atom-atom entanglement at the critical point, and has an important influence on the atom-atom entanglement behavior.     

Entanglement Dynamics and Bell Violations of Two Atoms in Tavis-Cummings Model with Phase Decoherence

Considering the dipole-dipole coupling intensity between two atoms and the field in the Fock state, the entanglement dynamics between two atoms that are initially entangled in the system of two two-level atoms coupled to a single mode cavity in the presence of phase decoherence has been investigated. The two-atom entanglement appears with periodicity without considering phase decoherence, however, the phase decoherence causes the decay of entanglement between two atoms, with the increasing of the phase decoherence coefficient, the entanglement will quickly become a constant value, which is affected by the two-atom initial state. Meanwhile the two-atom quantum state will forever stay in the maximal entangled state when the initial state is proper even in the presence of phase decoherence. On the other hand, the Bell violation and the entanglement do not satisfy the monotonous relation, a large Bell violation implies the presence of a large amount of entanglement under certain conditions, while a large Bell violation corresponds to a little amount of entanglement in certain situations. However, the violation of Bell-CHSH inequality can reach the maximal value if two atoms are in the maximal entangled state, or vice versa.     

Tavis-Cummings模型中两纠缠原子纠缠的演化特性

研究了两个纠缠的两能级原子与单模粒子数场进行相互作用系统中两原子的纠缠演化.结果表明：两个原子之间的纠缠呈现出周期性的演化特性，初始两原子的状态、原子之间的偶极相互作用和粒子数场对腔中两个原子的纠缠有着显著的影响.发现适当选择原子的初态，两原子会永远处于最大纠缠态. 关键词： 量子纠缠 偶极-偶极相互作用 部分转置矩阵负本征值 纠缠原子