THERMAL AND NON-UNIFORM MAGNETIC QUANTUM DISCORD IN THE TWO-QUBIT HEISENBERG XXZ MODEL

摘要

The thermal quantum discord (QD) is investigated in the two-qubit anisotropic Heisen- berg XXZ model under an external non-uni form magnetic field along the Z-axis. We obtain the analytical expressions of the thermal QD and thermal entanglement measured by concurrence (C). It shows that for any temperature T, QD gradually decreases with the increase of non-uniform magnetic field |b|, in some regions where C increases while QD decreases. It is also found that thermal quantum discord does not vanish at finite temperatures, but concurrence vanishes completely at a critical temperature. It is shown that for a higher value of Jz，the system has a stronger QD. There is a critical magnetic field B_c, which increases with the increasing b. QD decay monotonically (for B < B_c) when temperature T increases, or initially increases to some peaks and then decrease (for B > B_c).