Magnetic impurity effect on the entanglement in the Ising model

We study the effect of magnetic impurity on the entanglement in the three-site Ising model with both periodic and open boundary conditions. We obtain the analytic expressions for entanglement and show that the ground state and excited states of the system possess remarkable entanglement properties. We find that the entanglement between two specific spins for a given state depends on the sites where the impurities are located. We also discuss a relation of our results with some aspects of quantum phase transitions in the transverse Ising model. PACS numbers: 03.67.Mn, 03.65.Ud, 75.10.Jm (Some figures in this article are in colour only in the electronic version) 1