双量子系统任意态的条件熵纠缠度

从量子纠缠的熵特征-负值量子条件熵出发,我们提出了双量子系统任意态的新的纠缠量度-条件熵纠缠度.我们证明了条件熵纠缠度具有纠缠的单调性,满足作为一个好纠缠量度的基本条件.作为一个应用,我们利用条件熵纠缠度研究了同时与真空腔场相互作用的两个全同二能级原子之间的纠缠.我们讨论了两原子初态对所考虑系统条件熵纠缠度的演化,并将其演化规律与concurrence作了比较.我们的结果表明:条件熵纠缠度能够作为一个双量子系统任意态的、容易解析计算的纠缠量度.     

非旋波近似下Jaynes-Cummings模型中的场熵演化

研究了非旋波近似下Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ（Ｊ－Ｃ）模型中的场熵演化规律，并与旋波近似下的相应结果进行比较，讨论了虚光子过程对场熵演化的影响。     

Entanglement Dynamics of Atoms in Double Jaynes-Cummings Models with Kerr Medium

Entanglement dynamics of the atoms in the double Jaynes-Cummings models with the Kerr medium is studied, and the effect of the Kerr medium on that is examined. The result shows that, the Kerr medium can control the entanglement dynamics of the atoms and repress entanglement sudden death. We can obtain the maximum entanglement between the atoms by strengthening the nonlinear interaction of the Kerr medium.     

Coherence-Enhanced Entanglement Induced by a Two-Mode Thermal Field

Considering two identical two-level atoms interacting with two mode thermal field through a nondegerate two-photon process, we study the entanglement dynamics between two atoms when the atomic coherence exists. It shows that the entanglement is dependent on the initial atomic states, and is greatly enhanced due to atomic coherence as compared with the case when the atomic coherence is ignored. The results also show that the entanglement can be controlled by changing the relative phases and the amplitudes of the polarized atoms.     

Quantum Entanglement in a System of Two Spatially Separated Atoms Coupled to the Thermal Reservoir

We study quantum entanglement between two spatially separated atoms coupled to the thermal reservoir. The influences of the initial state of the system, the atomic frequency difference and the mean number of the thermal field on the entanglement are examined. The results show that the maximum of the entanglement obtained with nonidentical atoms is greater than that obtained with identical atoms. The degree of entanglement is progressively decreased with the increase of the thermal noise. Interestingly, the two atoms can be easily entangled even when the two atoms are initially prepared in the most mixed states.     

The squeezing dynamics of two independent atoms by detuning in two non-Markovian environments

The squeezing dynamics of two independent two-level atoms off-resonantly coupled to two non-Markovian reservoirs is studied by the time-convolutionless master-equation approach. We find that the squeezing of two atoms is dependent on both detuning and the non-Markovian effect. Our results show that, in the non-Markovian regime, the bigger the detuning and the stronger the non-Markovian effect are, the larger the strength of the squeezing is. And the squeezing of two atoms can be effectively protected for a long time when both the non-Markovian effect and detuning are present simultaneously. The physical mechanism is that the detuning not only can promote the feedback of information from the environment into the atomic system but also can greatly suppress the atomic decay in the non-Markovian regime.     

Entanglement dynamics of two-qubit systems in different quantum noises

The entanglement dynamics of two-qubit systems in different quantum noises are investigated by means of the operator-sum representation method.We find that,except for the amplitude damping and phase damping quantum noise,the sudden death of entanglement is always observed in different two-qubit systems with generalized amplitude damping and depolarizing quantum noise.     

Conservation issue of pairwise quantum discord and entanglement of two coupled qubits in a two-mode vacuum cavity

The conservation issues of pairwise quantum discord and entanglement of two qubits coupled to a two-mode vacuum cavity are investigated by considering the dipole-dipole interaction between two qubits.It is found that the sum of the square of the pairwise quantum discords and the sum of the square of the pairwise concurrences are both conserved in the strong dipole-dipole interaction limit.However,in the middle dipole-dipole and weak dipole-dipole interaction limits,the sum of the square of the pairwise concurrences is still conserved while the sum of the square of the pairwise discords is not.The crucial reason for this is that the quantum discords are not equivalent if the measurements are performed on different subsystems in a general situation.So it is very important for quantum computation depending on the quantum discord to select the target performed by the measurements.     

Sudden birth of entanglement between two atoms in a double JC model

Sudden birth of entanglement between two initially separate atoms interacting with two entangled photons in a double JC model is investigated, and the influences of different atomic initial states on entanglement among atoms are discussed. The results show that sudden birth of entanglement can occur when the two atoms are initially in excited states.     

The entanglement of two moving atoms interacting with a single-mode field via a three-photon process

In this paper, the entanglement of two moving atoms induced by a single-mode field via a three-photon process is investigated. It is shown that the entanglement is dependent on the category of the field, the average photon number N, the number p of half-wave lengths of the field mode and the atomic initial state. Also, the sudden death and the sudden birth of the entanglement are detected in this model and the results show that the existence of the sudden death and the sudden birth depends on the parameter and the category of the mode field. In addition, the three-photon process is a higher order nonlinear process.