横磁场中各向同性XY链的基态纠缠研究

分析了横磁场中各向同性XY自旋链的基态能量和纠缠问题。研究发现，三量子比特系统中存在一个相变点，此点上，基态能量和纠缠可发生量子相变，基态从W态进入非纠缠；而四量子比特系统存在两个相变点，基态的能量和纠缠均可在相变点处发生量子相变，使纠缠性质发生改变。随着磁场强度的增大，基态纠缠逐渐减小，直到完全消失。四比特系统纠缠的减小要比三比特系统纠缠减小的速度缓慢。

Research of Ground - state Entanglement in an Isotropic Transverse XY Chain

In this article, the ground state energy and entangled state problem in an isotropic transverse XY chain are analyzed. The research results show that only one phase transition point can be seen in a three - qubit system. The quantum phase transition process can be occurred between the ground state energy and entanglement, and the ground state can turn into disentangled state from W state. But the researchs found out that there are two transition points in a four - qubit system, and all the energy and entanglement can generate quantum phase transition in the phase points. And the entanglement properties can be changed through the phase points. With the increasing of the transverse, the entanglement of the ground state is decerased until disappeared completely. The decreased velocity of the entanglement in a four - qubit system is more slow than that of the entanglement in a three - qubit system.