Entanglement in the XZ spin chain model in the external magnetic field

Abstract

The entanglement at zero-temperature is studied in a two-qubit XZ spin-1/2 chain model in an<br />external magnetic field which is applied in the z direction. We have obtained an analytical relation for<br />the effect of the external magnetic field on the concurrence. It is shown that the ground state of the<br />system depends on the strength of exchange coupling. We have shown that the analytical relation of<br />the concurrence is independent of Jz. It is shown that for Jz >0 the concurrence is depended on the<br />critical value of the external magnetic field and it is changed at the critical external magnetic field.<br />Also we have shown that for h <hc the concurrence is maximum (C=1) or states of the system are<br />maximally entangled. For values of the field h>hc, the concurrence decreases by increasing the<br />external magnetic field. For Jz <0, the concurrence decreases by increasing the external magnetic<br />field.