中文摘要：

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。

英文摘要：

In this paper,we investigate the entanglement dynamics of two entangled two-level atoms with initial X state and dipole-dipole coupling intensity in Tavis-Cummings model.The interesting phenomena of entanglement sudden death as well as sudden birth appear during the evolution process.We analyze in detail the effect of purity of initially entangled state of two atoms,the dipole-dipole coupling intensity between two atoms,and the field in the Fock state on the apparition time of entanglement sudden death and entanglement sudden birth.Furthermore,the conditions for the conversion of entanglement sudden death and entanglement sudden birth can be generalized when the initial entangled state is not pure.The results show that the above system parameters affect the concurrence,entanglement sudden birth and sudden death remarkably,the dipole-dipole coupling intensity affects amplitudes of the concurrence oscillation and leads time interval of the ESD to decrease.With the increasing of the purity,the time of entanglement sudden death and entanglement sudden birth will decrease;it is also notable that invariant and stable entanglement,which can be controlled by different initial states of the atoms,occurs for particular initial X state.