非均匀海森堡XY周期性链的纠缠

研究了各向同性海森堡XY链在非均匀磁场中纠缠的含时演化以及热纠缠的问题。纠缠在量子信息领域是个十分重要的资源，关于纠缠的度量和含时演化的研究就非常必要。我们主要对共生纠缠度进行了理论计算，通过数值模拟进行了分析。如果外磁场很小，最近邻耦合系数很大，共生纠缠度就在0和1之间振荡。如果外磁场很大，最近邻耦合系数很小，共生纠缠度的最大值会变小，甚至会消失。同时，随着海森堡自旋链中自旋数目的增加，纠缠会减小。随着温度的升高，热纠缠会快速的下降。随着外磁场的增加，热纠缠也会下降。只有在系统的非均匀度增加的时候，热纠缠才会增加。

Entanglement of Heisenberg XY model on inhomogeneous periodic chain

The time evolution of entanglement and thermal entanglement of an isotropic XY model on the inhomogeneous chain is investigated when there is anisotropic magnetic field. Since entanglement is a very important resource in the field of quantum information, the study of measure and time evolution of entanglement is necessary. The quantity of concurrence was theoretically calculated and it was analyzed by numerical simulations. If the external magnetic field is small and the nearest neighbor coupling is large, the concurrence oscillates between zero and one. If the external magnetic field is large and the nearest neighbor coupling is small, the maximum concurrence can be reduced and even disappears. Meanwhile, the entanglement decreases when the number of spins in the Heisenberg chain increases. The thermal entanglement drops quickly when the temperature increases. It decreases also as the external magnetic field increases. It increases if the inhomogeneity of the system increases.