与热库耦合的光学腔内三原子间的纠缠动力学

研究了与热库耦合的光学腔中三个相互作用的二能级原子间的纠缠动力学.采用拉普拉斯变换和下限共生等方法,通过数值计算,分析了原子间三体纠缠的演化以及腔场与热库间的两体纠缠演化,讨论了各耦合参数对系统纠缠演化的影响.研究结果表明:原子间纠缠在短时间内随着原子间耦合强度的增加而增加,随原子与腔场耦合强度的增加而减小,在长时极限下趋于一稳定值;体系的非马尔科夫性由原子与腔场的耦合强度以及热库的谱宽度共同决定,当热库与腔场为强耦合时,原子与腔场组成的系统遵循非马尔科夫动力学,此时随着热库谱宽的增加,原子系统由非马尔科夫性变为马尔科夫性,随着谱宽的继续增加,原子与腔场组成的系统遵循马尔科夫动力学,原子系统又表现出非马尔科夫性;调整腔场与热库的失谐可以有效抑制热库耗散对纠缠衰减的影响.     

耦合双Tavis-Cummings模型中的纠缠演化和转移特性

研究了由光纤模连接的两个Tavis-Cummings模型中纠缠演化和纠缠转移的特性。结果表明,初始两原子间的纠缠可转移为另两原子间的纠缠,在纠缠转移过程中,光纤模起到中间传递的作用。纠缠的转移与初始两原子间的纠缠、原子与腔场的耦合强度以及光纤模与腔场的耦合强度、原子与腔场的失谐量和腔场耗散有关。初始纠缠决定了另两原子间纠缠产生的大小;在原子与腔场的耦合强度一定的条件下,随着光纤模与腔场耦合强度的增强,纠缠转移的时间缩短,且产生的纠缠值增加;腔场耗散对纠缠演化的衰减影响是显著的,而失谐量的增加可以有效地抑制这一现象。在整个纠缠转移过程中,系统中其他任两子体系间的纠缠起到了桥梁的作用,实现了两量子纠缠态的远程传递和制备。     

耦合系数对Tavis-Cummings模型中三体纠缠态纠缠量的影响

研究了两个全同二能级原子与单模场相互作用的Tavis-Cummings模型中的量子纠缠.在两原子初始时处于基态,光场处于单光子状态下,得出体系状态演化为近似W纠缠态.结果表明:两原子耦合量越大,三体纠缠态中两两纠缠量和三体纠缠量越小,其中两原子间纠缠量和三体纠缠量减小的程度更大,并且三体纠缠态中两两纠缠量和三体纠缠量的振荡周期也相应减小.     

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.     

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.     

Entanglement in a system of two two-level atoms interacting with a single-mode field

We investigate the entanglement in a system of two coupling atoms interacting with a single-mode field by means of quantum information entropy theory. The quantum entanglement between the two atoms and the coherent field is discussed by using the quantum reduced entropy, and the entanglement between the two coupling atoms is also investigated by using the quantum relative entropy. In addition, the influences of the atomic dipole--dipole interaction intensity and the average photon number of the coherent field on the degree of the entanglement is examined. The results show that the evolution of the degree of entanglement between the two atoms and the field is just opposite to that of the degree of entanglement between the two atoms. And the properties of the quantum entanglement in the system rely on the atomic dipole--dipole interaction and the average photon number of the coherent field.     

原子与光纤耦合腔相互作用系统中的纠缠特性

研究了光纤耦合腔A和B中各囚禁一个和两个二能级原子的情况,给出了总激发数为1时系统态矢的演化。采用Negativity熵来描述两个子系统间的纠缠,利用数值计算方法研究了腔内原子与原子间和腔场与腔场间的纠缠特性,讨论了光纤模与腔场间的耦合强度变化对纠缠特性的影响。另一方面还研究了对腔A中原子选择性测量对纠缠特性的影响。研究结果表明:随光纤模与腔场间的耦合系数增大,腔场间纠缠减弱。原子间纠缠与光纤模与腔场间的耦合系数间存在非线性关系。另一方面,采用原子态选择性测量方法,可增强腔内原子间和腔场间的纠缠。     

驱动两能级原子和真空场相互作用系统中纠缠突然死亡的操控

利用并发度和线性熵作为纠缠度量研究了两个驱动两能级原子和真空场相互作用系统中的纠缠动力学特性,分析了经典驱动场频率、原子和经典场的耦合系数以及参数α对并发度和线性熵的影响。结果发现通过调控经典驱动场能够提高两原子之间和两原子与场之间的纠缠,实现两原子之间纠缠突然死亡现象的操控,理论上提供了一种调控纠缠的方式。     

Entanglement Dynamics of Two V-type Atoms with Dipole–Dipole Interaction in Dissipative Cavity

In this work, a coupled system of two V-type atoms with dipole–dipole interaction in a dissipative single-mode cavity, which couples with an external environment, is studied. The analytical solution of this model is obtained by solving the time dependent Schrodinger equation after Hamiltonian of dissipative cavity is diagonalized by introducing a set of new creation and annihilation operators according to Fano theorem. It is also discussed in detail how the entanglement dynamics of different initial states are influenced by the cavity-environment coupling, the spontaneously generated interference (SGI) parameter, and the dipole–dipole interaction between two atoms . The results show that the SGI parameter has different effects on entanglement dynamics under different initial states. Namely, the SGI parameter will increase the decay rate of the initially maximal entangled state and reduce that of the initially partial entangled state. For the initially product state, the larger SGI parameter corresponds to the more entanglement generated. The entanglement monotonically decreases under the weak cavity-environment coupling, while the oscillation of entanglement will occur under the strong cavity-environment coupling. The larger the dipole–dipole interaction is, the slower the entanglement decays and the more the entanglement will be generated. So the dipole–dipole interaction can not only protect and generate entanglement very effectively, but also enhance the regulation effect of the SGI parameter on entanglement.     

Quantum Entanglement Dynamics of Two Atoms in Two Coupled Cavities

Quantum entanglement dynamics for two atoms trapped in two coupled cavities is investigated.Numerical results show that the present of the two atomic excitations is mainly accounted for the entanglement-sudden-death(ESD) effect with the two cavities initially in the vacuum.The entanglement can also be controlled by the hopping rate and the imbalances between the two atom-cavity coupling rates.     

Entanglement transfer between atoms in two distant cavities via an optical fibre

This paper presents a treatment of the entanglement transfer between atoms in two distant cavities coupled by an optical fibre. If the atoms resonantly and collectively interact with the local single-mode cavity fields and the dipole--dipole interaction between the atoms is neglected, then it shows that a complete transfer of entanglement from one pair of atoms to another can be deterministically realized. Furthermore, it also investigates the effects of dipole--dipole interaction on entanglement transfer on the condition that the interaction between the atoms and the cavity is much weaker than the coupling between the cavity and the fibre.     

The entanglement between two isolated atoms in double mode--mode competition model

Extending the double Jaynes--Cummings model to a more complicated case where the mode--mode competition is considered, we investigate the entanglement character of two isolated atoms by means of concurrence, and discuss the dependence of atom--atom entanglement on the different initial state and the relative coupling strength between the atom and the corresponding cavity field. The results show that the amplitude and the period of the atom--atom entanglement evolution can be controlled by the choice of initial state and relative coupling strength, respectively. We find that the phenomenon of entanglement sudden death (ESD) is sensitive to the initial conditions. The length of the time interval for zero entanglement depends not only on the initial degree of entanglement between two atoms but also on the relative coupling strength of atom--field interaction. The ESD effect can be weakened by enhancing the mode--mode competition between the three- and single-photon processes.     

Formation of three-body entanglement via a vacuum optical cavity induction in Tavis-Cummings model

After briefly introducing Akhtarshenas, concurrence vector and subvector for describing many-body entanglement, we investigate the entanglement formation for a system which contains three bodies, i.e. two identical atoms and a single- model cavity field, in the Tavis-Cummings model by calculating the concurrences. The results show that the coupling strength between two atoms, the decay cavity and the atomic spontaneous emission can change the entanglement of formation according to different modes： these factors destroy periodicity and symmetry of all concurrences, and that the coupling strength of two atoms does not change the peak value of concurrence （C）, but the strength of decay cavity and the atomic spontaneous emission decline in the peak value of concurrence （C） and the latter is more serious than the former under the same strengths. The concurrence vector and subvector are a useful measure of entanglement for a pure state of the many-body system, in that it can give novel pictures about the entanglements for the entire system and between its inner bodies.     

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     

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     

强度相关耦合双Jaynes-Cummings模型中的纠缠和量子失谐

研究强度相关耦合双Jaynes-Cummings模型中, 两运动原子初始处于最大纠缠态、光场初始处于单模热态时, 强度相关耦合、热光场平均光子数以及原子运动对两原子的纠缠和量子失谐的影响. 结果表明: 考虑强度相关耦合时, 纠缠和量子失谐均出现周期性地消失和回复现象, 并且, 回复以后的纠缠和量子失谐能达到初始值. 腔场温度的升高会加速纠缠和量子失谐的消失. 此外, 原子运动的场模结构参数对该模型中的纠缠和量子失谐影响很大, 其值选择合适时, 两个原子能够自始至终地保持纠缠或量子失谐状态. 关键词： 强度相关耦合 双Jaynes-Cummings模型 纠缠 量子失谐     

两原子与数态场相互作用系统中纠缠的调控

通过计算并发度研究了两个处于初始激发态的两能级原子与数态场相互作用系统的纠缠动力学特性,并讨论了场的光子数、原子和场的失谐量以及原子操作对并发度的影响。结果表明当不存在原子操作时,两原子之间的纠缠出现突然产生现象,并且可以通过调节光子数和原子与场的失谐量来控制产生纠缠的阈值时间和纠缠的最大值。当存在原子操作时,两原子之间的纠缠随着时间的演化可以立即产生,而且通过对经典场的操作和控制可以实现两原子之间纠缠的调控。     

Entanglement swapping between atom and cavity and generation of entangled state of cavity fields

This paper proposes a scheme where entanglement swapping between atom and cavity can be realized. \Lambda -type three-level atoms interacting resonantly with cavity field are considered. By detecting atom and cavity field, it realizes entanglement swapping between atom and cavity. It uses the technique of entanglement swapping to generate an entangled state of two cavity fields by measuring on atoms. It discusses the experimental feasibility of the proposed scheme and application of entangled state of cavity fields.     

Effect of the Time-Dependent Atom-Field Couplings on Entanglement

A model containing two two-level atoms and a single-mode cavity is considered, and the effect of the time-dependent atom-field couplings on entanglement between the two atoms is studied. The results indicate that both for one-photon processes and for two-photon processes, the disappearance of the initial entanglement is delayed due to the linear modulation of the atom-field coupling coefficients as compared to the constant coupling model. The delayed time of the disappearance of the initial entanglement for the two-photon processes is much longer than that for the one-photon processes in the case of adiabatic variation.     

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.