非匀强磁场中双量子位Heisenberg XY链的基态纠缠和热纠缠

摘要

We study the entanglement of thermal and ground states in the Heisenberg XY spin chain with an inhomogeneous magnetic field. A general result is found that for two-qubit case, pairwise entanglement is independent of the sign of coupling constant J, magnetic field B, anisotropic parameter γ and inhomogeneous parameter b of the magnetic field. At zero absolute temperature, an analytical expression of concurrence C is given through which we show that the critical magnetic field Bc increases with the increase of inhomogeneity.At finite temperature, we show analytically for the isotropic case and numerically for the anisotropic case that the thermal entanglement can be apparently enhanced by introducing the inhomogeneity of the magnetic field.We also show that for isotropie case the critical temperature Tc is alone an increasing function of the inhomogeneous parameter b, while for anisotropic case, it is determined by both B and b.%研究了非匀强磁场中各向异性Heisenberg XY链的基态纠缠和热纠缠.结果表明对双量子位情形,纠缠与格点间耦合常数J、外部磁场B、各向异性参数γ和b的正负无关.对绝对零度情形,我们给出了纠缠C的解析表达式,并指出临界磁场Bc随磁场各向异性参数b的增大而增大.对有限温度情形,我们给出了γ=0时C的解析表达式和γ≠0时的数值模拟结果,结果发现引进非匀强磁场可以使纠缠在某些区域明显增大;同时我们还指出当γ=0时,纠缠存在的临界温度Tc仅是b的增函数,而当γ≠0时,它却由B和b共同决定.