耦合系数的线性变化对量子纠缠的调控

考虑原子－光场耦合系数随时间变化的双Jaynes－Cummings模型组成的系统,研究两原子初始处于最大纠缠态时,耦合系数的线性调制对原子纠缠的影响。结果表明：初始纠缠保持时间的长短与耦合系数的线性调制密切相关。无论是单光子过程还是双光子过程,较耦合系数为常数的情形而言,耦合系数线性调制下的初始纠缠消失的时间被大大延迟,延迟时间的长短与耦合系数线性调制的参数选择密切相关,并且在双光子过程中延迟的时间更长。     

运动原子与双光子相互作用模型中的纠缠与热纠缠

利用共生纠缠度,研究了运动原子与单模腔场发生双光子相互作用模型的纠缠与热纠缠现象.结果表明:初始光子数和腔模半波数对纠缠度和热纠缠度的演化周期有一定影响,而原子与腔场的耦合系数不会改变纠缠度的演化周期,但耦合系数减小时,系统处于最大纠缠态的时间减少;在临界温度之下,环境温度增加会使系统纠缠度变小.     

压缩态光场变耦合系数双光子J-C模型性质

讨论了初始光场为压缩态、原子-光场耦合系数随时间变化情形下双光子过程J-C模型的量子统计性质。具体研究了双光子过程中原子布居数反转、光场的压缩等随时间的演化性质,讨论了初始光场的压缩系数、压缩相位及耦合系数变化快慢对这些性质的影响。研究结果表明,初始光场的压缩系数增大,崩塌和回复的频率增大,回复值减小。当原子-光场耦合系数变化缓慢时,崩塌和回复现象被延迟。而光场逐渐失去压缩性质;而当耦合系数变化较快时,崩塌和回复现象被加速,而光场压缩量将产生振荡,压缩效应将反复出现。     

三耦合腔系统双光子过程中的纠缠特性

研究腔与腔之间通过双光子过程耦合的三耦合腔系统,考虑每个腔囚禁一个二能级原子,并且原子通过双光子跃迁过程与腔场共振相互作用的情况。采用负本征值来度量两个子系统间的纠缠,利用数值计算方法研究了系统中两个子系统间的纠缠动力学特性。讨论了腔场间耦合系数变化对两个子系统间纠缠特性的影响。研究发现,随腔场间耦合系数的增大,两原子间的纠缠增强,两腔场间的纠缠减弱。     

双光子Tavis-Cummings模型中的量子纠缠

我们对两个全同二能级原子通过双光子跃迁与单模辐射场发生相互作用的Tavis-Cummings(T-C)模型中的量子纠缠特性进行了研究.通过数值计算与分析,结果表明:双光子T-C模型的量子纠缠比单光子T-C模型的量子纠缠要保持得好一些;另外分析了双光子T-C模型中原子间偶极-偶极相互作用强度系数、原子与场的耦合系数、光子数对两原子间纠缠特性与场熵的影响.     

原子与双模相干强场依赖强度耦合多光子过程中纠缠量度与制备

给出了依赖强度耦合双模多光子过程Jaynes-Cummings模型的有效哈密顿量.在强场条件下,分别用量子约化熵和量子相对熵研究了上述模型中原子与场之间的纠缠以及双模相干场的模间纠缠演化.研究表明,这两类纠缠演化均与原子跃迁时吸收(或发射)的光子数k密切相关.同时,还揭示了双光子过程(k=1)和多光子过程(k≥2)中不同的纠缠特性.讨论了纠缠态的制备,制备了与时间无关的原子-场的Einstein-Podolsky-Rosen态和双模相干场的模间纠缠态.     

耗散腔中多光子J-C模型中的密度算符间距

研究了腔场存在相位耗散时多光子J-C模型中光场、原子和系统的密度算符间距;讨论了原子初始态、光场强度以及腔场耗散系数对密度算符间距的影响;且比较了不同跃迁光子数下体系的密度算符间距。结果发现：①密度算符间距与原子的初始态密切相关。②光场和系统的密度算符间距在耗散腔中作减幅周期振荡最终达到稳定,达到稳定所需时间随腔的耗散系数增大而缩短;而原子的密度算符间距与腔的耗散无关。③随着光场初始强度的增加,光场和系统与各自初始态的偏离程度增大。④对于双光子跃迁,当腔场存在相位损耗时光场和系统的密度算符间距仍作减幅周期振荡,原子仍周期性的回到纯态。但由于光场与原子的纠缠和退纠缠速率加快,密度算符间距在每个周期内振荡加剧。     

耗散腔中多光子J-C模型中的密度算符间距

研究了腔场存在相位耗散时多光子J-C模型中光场、原子和系统的密度算符间距;讨论了原子初始态、光场强度以及腔场耗散系数对密度算符间距的影响;且比较了不同跃迁光子数下体系的密度算符间距.结果发现:①密度算符间距与原子的初始态密切相关.②光场和系统的密度算符间距在耗散腔中作减幅周期振荡最终达到稳定,达到稳定所需时间随腔的耗散系数增大而缩短;而原子的密度算符间距与腔的耗散无关.③随着光场初始强度的增加,光场和系统与各自初始态的偏离程度增大.④对于双光子跃迁,当腔场存在相位损耗时光场和系统的密度算符间距仍作减幅周期振荡,原子仍周期性的回到纯态.但由于光场与原子的纠缠和退纠缠速率加快,密度算符间距在每个周期内振荡加剧.     

非旋波近似下双光子Jaynes—Cummings模型的量子特性

在非旋波近似下对双光子Jaynes-Cummings(J-C)模型与单模相干态光场相互作用的量子特性进行了精确求解。对双光子J-C模型与单光子J-C模型量子纠缠和原子布居数反转的演化特点进行了对比,讨论了平均光子数、光场与原子之间的耦合强度以及失谐对量子纠缠以及原子布居数反转的影响,数值计算的结果表明,随着光场与原子之间耦合强度的增大,量子纠缠的周期性逐渐消失,随着平均光子数的增加,纠缠达到较稳定的最大值所需时间逐渐增大。无论耦合强度、平均光子数还是失谐的增大,由非旋波项产生的虚光子效应逐渐增强,量子纠缠演化曲线和原子布居数反转的塌缩区出现小锯齿状振荡。     

Stark位移对热环境下双Jaynes-Cummings模型中原子纠缠的影响

研究双光子跃迁的双Jaynes-Cummings模型中, 两原子初始处于最大纠缠态、光场初始处于单模热态时的原子纠缠动力学, 考虑双光子过程中的Stark位移、热光场的平均光子数对原子纠缠的影响. 结果表明: 不考虑Stark位移时, 两原子在系统演化过程中周期性地出现退纠缠现象, 而考虑Stark位移时, 两原子长时间地纠缠. 特别是当Stark位移参数取值较大且热光场的平均光子数值比较小时, 两原子能保持 稳定地纠缠. 这些结果表明, 可以利用Stark位移对热环境下双Jaynes-Cummings模型中的原子纠缠进行调控.     

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.     

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.     

Complete entanglement transfer between light and qubits

Using the two-mode two-photon Jaynes-Cummings model, entanglement transfer between atoms and field is studied. It is found that when the field is in state constructed from the two-mode photon number states |00〉,|11〉 or the two-mode squeezed vacuum states, full entanglement exchange can be attained no matter the atoms are initially in pure or mixed states. These investigations show that CV entangled states can act as perfectly as the entangled number states in entangling initially separable atoms. The two-mode two-photon atom-field interaction also provides a simple way for the quantum teleportation of atomic or field states.     

Entanglement Dynamics of the Double Intensity-Dependent Coupling Jaynes-Cummings Models

We consider entanglement dynamics of double intensity-dependent coupling Jaynes-Cummings models with two different initial light fields, which one is in the squeezed vacuum state and another is in the coherent state. The results show that, when the compressibility factor and the mean photon number are smaller, the concurrence of atoms exhibits phenomenon of dead and revival periodically, and the entanglement perfectly transferres between the atoms and the fields. As the value of them grow larger, the entanglement sudden death and sudden revival come out. Comparing with the normal double Jaynes-Cummings model, we notice that the concurrence of the atoms which in the normal double Jaynes-Cummings models evolves irregularly. And it is find that periodical entanglement pulse can be generated by using double intensity-dependent coupling Jaynes-Cummings models. This result might be useful in quantum information processes.     

Control of Sudden Death of Entanglement by Transient Effects

We investigate the properties of entanglement between an isolated atom and a Jaynes-Cummings atom in the presence of transient effects. These effects are due to the modulation of the atom-field coupling whose explicit time-dependence is considered for the case of the linear sweep. We show that the sudden death of entanglement can be controlled by the transient effects. These effects can suppress the sudden death of entanglement in time.     

The entanglement of two dipole--dipole coupled atoms interacting with a thermal field via a two-photon process

This paper studies entanglement between two dipole-dipole coupled atoms interacting with a thermal field via a two-photon process. It shows that the entanglement is dependent on the mean photon number of the thermal field and the dipole-dipole interaction. The results also show that the atom-atom entanglement through the two-photon process is larger than that through the one-photon process and a remarkable amount of entanglement between the atoms still remains at certain times even for a very highly noisy thermal field.     

The entropy of entangled three-level atoms interacting with entangled cavity fields: Entanglement swapping

The dynamics of an entangled atomic system, partially interacting with entangled cavity fields and characterizing an entanglement swapping, has been studied through their von Neumann entropies. The aforementioned interaction is implemented via a two-photon process, given by either the full microscopical Hamiltonian approach or the two-photon Jaynes-Cummings model. Numerical simulations furnish the explicit expressions for each sub-system entropy, which allow us to estimate the multiperiodicity in the evolution of the entangled atom-field system. The effects of the detuning parameter upon the period and the amplitude of the entropies are also discussed as well as the power spectrum of the entropy.