Impurity entanglement in spin-1 Heisenberg XX chain

We investigate the impurity entanglement of the ground states and the thermal states at finite temperature for a three-qutrit system of the Heisenberg XX model in the presence of a uniform magnetic field. As a measure of the entanglement, negativity of the state is analyzed in detail as a function of the impurity parameter, temperature and magnetic fields. Magnetic fields are mainly to reduce entanglement. Impurity parameter plays an important role in enhancing the entanglement and improving the critical temperature. We can use them to control entanglement. (authors)