Influences of Detuning on Geometrical Quantum Discord Dynamics in Double Jaynes-Cummings System

We consider the case that the two-level atom off-resonantly interacts with cavity field via a one-photon hopping in double Jaynes-Cummings system. Geometrical quantum discord (GQD) is adopted to quantify the degree of correlation between two subsystems. GQD dynamics between two atoms, between cavity fields, as well as between atom and cavity fields are studied. The influences of detuning on GQD are discussed. The results obtained using the numerical method show that GQD between two atoms, between cavity fields, and between atom and cavity fields all display periodic oscillations. Furthermore, their periodic oscillations frequencies increase with the increase of detuning. On the other hand, GQD between two cavity fields and that between atom and cavity are weakened with increase of detuning.

     

原子与耦合腔相互作用系统中的量子失协

本文研究由两个全同的二能级原子和耦合腔构成的系统,利用Dakic等提出的几何量子失协的度量方法,采用数值计算方法计算了系统中两原子间和两腔场间量子失协的演化.讨论了原子间初始纠缠度和腔场间耦合系数变化对几何量子失协演化的影响.研究发现:随腔场间耦合系数的增大,量子失协周期性演化的频率增大;随原子间初始纠缠度的增大,两原子间的关联增强,两腔场间的关联减弱.     

The Entanglement Properties in the Coupled-Cavity System with the Detuning between an Atom and Cavity Field

We consider the situation that two atomic ensembles are separately trapped in coupled single-mode cavities, and each atom non-resonantly interacts with cavity field via a one-photon hopping. By employing the negativity measure of entanglement, we investigate the temporal evolution of entanglements between the cavities as well as between the cavity and atomic ensemble. By means of the numerical calculations, we discuss the influences of the number of atoms in an atomic ensemble and the detuning on the entanglement. The results show that as the number of atoms increases, the entanglement between the cavities is strengthened, contrary the entanglement between atomic ensemble and cavity is weakened. On the other hand, as the detuning increases, the entanglement between the cavities is weakened, contrary the entanglement between atomic ensemble and cavity is strengthened.

     

Generation of multipartite entangled states by cavity QED

We propose the methods of generating multipartite entanglement by considering the interaction of a system of N two-level atoms in M cavities of high quality factor with a strong classical driving field. It is shown that, with the cavity detuning, the applied driving field detuning and vacuum Rabi coupling, we can produce an entangled coherent state in two single-mode cavities and generate the entangled coherent cluster states in two bimodal vacuum cavities. Tuning these parameters also allows us to acquire the anti-Jaynes-Cummings （AJC） interaction, with which we can generate the maximally two-photon entangled states, and the two-atom and the two-photon entangled cluster states.     

阻尼Jaynes-Cummings模型中两原子的量子关联动力学

几何量子失协 (geometrical quantum discord, GQD)是目前度量量子体系中量子关联的一种行之有效的方法, 本文利用几何量子失协考察了有阻尼存在的Jaynes-Cumming (J-C)模型中两原子的量子关联动力学. 给出了几何量子失协在原子和光场发生共振和非共振耦合两种情况下的动力学演化行为, 尤其揭示了阻尼耗散对几何量子失协的影响. 关键词： 阻尼Jaynes-Cummings(J-C) 模型 量子关联 几何量子失协 (GQD)     

Control of sudden transition between classical and quantum correlations of two strongly driven atoms in dissipative cavities

We investigate analytically the dynamics of classical and quantum correlations between two strongly driven atoms, each of which is trapped inside a dissipative cavity. It is found that there exists a finite time interval during which the quantum discord initially prepared in the X-type states is not destroyed by the decay of the cavities. The sudden transition between classical correlation and quantum discord is sensitive to the initial-state parameter, the cavity decay rate, and the cavity mode-driving field detuning. Interestingly, we show that the transition time can be prolonged significantly by increasing the degree of the detuning.     

Generation of cluster states in thermal cavity

A scheme is reported for generating a multi-atom cluster state in thermal cavities, which is based on the simultaneous interaction of two two-level atoms with a single-mode cavity field driven by a classical field. The photon-number-dependent parts in the evolution operator are cancelled with the assistant of a strong classical field, so the scheme is insensitive to the thermal field. In the present scheme, the detuning between the atoms and the cavity is equal to the atom-cavity coupling strength, thus the operation speed is greatly improved, which is important in view of decoherence.     

Quantum correlations between two cavity QED systems coupled by a mechanical resonator

Achieving quantum correlations between two distant systems is a desirable feature for quantum networking. In this work, we study a system composed of two quantum emitter-cavity subsystems spatially separated. A mechanical resonator couples to either both quantum emitters or both cavities leading to quantum correlations between both subsystems such as non-local light-matter dressed states and cavity–cavity normal mode splitting. These indirect couplings can be explained by an effective Hamiltonian for large energy detuning between the mechanical resonator and the atoms/cavities. Moreover, it is found that the optimal conditions of the physical parameters maximize the entanglement of phonon-mediated couplings.     

Dynamical behavior of entanglement, purity and energy for two atoms in the presence of dissipation

Entanglement, purity and energy of two isolated two-level atoms which are initially prepared in Bell state and each interacts with a dissipative thermal cavity field are investigated with considering the atomic motion and the field-mode structure. We give the analytical solution of the atomic state by using the algebraic dynamics approach. The influences of the field-mode structure, the dissipation of the cavities, the strength of the thermal field and the detuning on the entanglement, purity and energy are discussed. We also study the evolution of the atomic state using the entanglement-purity-energy diagrams. Our results suggest that the disentanglement process of the atomic state accompanies with the excitations transferring from atoms to the cavity field modes and with the state converting from a pure one to the mixed ones. When the two atoms become separable, they must be in the mixed states, and their energy decreases with the increase of the purity.     

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.     

Λ型和V型三能级原子与耦合腔相互作用系统中的纠缠特性

研究了由一个Λ型三能级原子、一个V型三能级原子和光纤连接的双模腔构成的系统,给出了系统态矢的演化. 采用部分转置密度矩阵的负本征值来描述两个子系统间的纠缠,利用数值计算方法研究了原子与原子之间和腔场与腔场之间的纠缠特性. 讨论了光纤模与腔场间的耦合强度对纠缠特性的影响. 研究结果表明:随光纤模与腔场间的耦合强度增强,原子间的纠缠和腔场间的纠缠均增强. 关键词： 量子光学 原子-腔-光纤复合系统 三能级原子 量子纠缠     

Entanglement and Bell violation with phase decoherence or dissipation

The system of an atom couples to two distinct optical cavities with decoherence is studied by making use of a dynamical algebraic method. We adopt the concurrence to characterize the entanglement between atom and cavities or between two optical cavities in the presence of the phase decoherence or dissipation. It is found that the entanglement between atom and cavities can be controlled by adjusting the detuning parameter. We show that even if the atom is initially prepared in a maximally mixed state, it can also entangle the two mode cavity fields. Finally, the Bell violation of the cavity fields is discussed, and it is shown that both the detuning and decoherence can deteriorate the maximal amount of violation of Bell inequality for two mode cavity fields during the evolution.     

Continuous variable entanglement generation in coupled cavities

We investigate continuous variable entanglement produced in two distant coupled cavities, in which two four-level atoms are driven by classical fields respectively. Under the large detuning condition, an effective Hamiltonian containing the square of the creation (annihilation) operator of the cavity field is derived. Due to the nonlinearity, entanglement formally created by the beam splitter type interaction is transformed into the nondegenerate parametric down conversion type. Employing the operator algebraic method, we study the time evolution of the entanglement condition, and show that the system provides us an advantage in achieving a larger photon number with better entanglement. We also discuss the dissipation of the cavities affecting the entanglement.     

有心结构耦合腔系统中的几何量子失谐（英文）

引入了由N+1个单模腔构成的有心结构耦合腔物理模型.其中,中心腔起耦合器作用,其余N个腔通过N条光纤与中心腔耦合,并且每个腔囚禁1个二能级原子.在系统激发数等于1的情况下,给出了系统态矢的演化规律,研究了两原子间和两腔场间的几何量子失谐.通过数值计算,讨论了耦合腔数目和原子与腔场间耦合强度对几何量子失谐的影响.研究结果表明:随着腔数目的增加两原子间和两腔场间的几何量子失谐都减弱;随着原子与腔场间耦合系数增大,两原子间几何量子失谐减弱,但两腔场间几何量子失谐却加强.     

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     

Entanglement Properties in a Star Structure Coupled Cavities System

In this paper, the star structure coupled cavities system is composed of six single-mode cavities. One of them is at the center of the star structure, and other five cavities are at the five vertices of the star structure, respectively. The center cavity is connected with other five cavities by optical fibers. The situation is considered that six identical two-level atoms are separately trapped in six single-mode optical cavities, each atom resonantly interacts with cavity via a one-photon hopping, and the total excitation number of the system equals one. Negativity is adopted to quantify the degree of entanglement between two subsystems. The entanglement properties between atoms and that between cavities are investigated. The influences of atom-cavity coupling coefficient on the entanglement properties between two subsystems are studied. The results obtained using the numerical method show that the atom-atom entanglement is weakened, and the cavity-cavity entanglement is strengthened with the increase of atom-cavity coupling coefficient.

     

三个耦合腔系统中的纠缠特性

本文研究将三个二能级原子分别囚禁在耦合腔A, B和C中, 腔中原子与腔场发生共振相互作用的情况. 采用Negativity熵度量两子系统间的纠缠, 通过数值计算给出了两个原子之间和两个腔场之间的纠缠演化. 讨论了腔场间的耦合强度对纠缠特性的影响. 研究结果表明: 原子间的纠缠与腔场间的耦合系数间存在非线性关系. 另一方面, 相邻腔场腔A和腔B间, 以及腔B和腔C间的纠缠随腔场间的耦合系数增大而减弱, 但非相邻腔场腔A和腔C间的纠缠却随腔场间的耦合系数增大而增强.     

Entanglement between two qubits interacting with a slightly detuned thermal field

In this paper, we investigate entanglement between two two-level atoms when they simultaneously interact with a single-mode thermal field in the strong-coupling regime. We show that a slight detuning between the atomic transition frequency and the field frequency might cause high entanglement between the atoms. More interestingly, if we choose the detuning appropriately, both atoms would somehow get entangled even when both atoms are initially in the excited state.     

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.     

非共振耗散腔耦合系统的发射光谱

研究了非共振耗散二能级双原子与双单模腔耦合系统发射光谱的性质。探讨了原子和腔场之间的失谐、腔场衰减率及原子失相对该系统发射光谱的影响。结果表明,体系的腔场谱呈现出三重峰结构,原子发射谱呈现出二重峰结构。非共振情况时,腔场谱和原子发射谱的图像皆为非对称图像。在原子与腔场失谐时,与共振情况相比,峰位发生了明显的漂移,且中峰明显增大。增大腔场与原子的失谐,会引起边峰向低频段漂移,并改变其光谱强度;增大原子与腔场的失谐,可以使光谱整体向低频段漂移,并改变其所有峰的光谱强度。随着腔场衰减率的增大,共振情况下,会导致边峰的强度减小;失谐情况下,会导致所有峰的强度均减小。随着原子失相的增大,共振或失谐情况下,会使光谱所有峰的强度均减小。