Quantum entanglement investigation on impurity effects in the transverse Ising chain

The impurity effects of the transverse Ising spin model with a magnetic impurity are investigated via the correlation function and entanglement on the basis of an exact solution. The non-analytical transition point from an ordered phase to a disorder phase is significantly shifted by the impurity coupling with local host spins. The maximal entanglement point which usually appears around the critical point shows strong dependence on the impurity coupling strength with local host spin and the independent transverse field upon the impurity itself. Quantum entanglement in disordered spin phase is much stronger than that in ordered spin phase. The exact concurrence of impurity spin with local host spin suddenly increases to a large value from zero at a threshold value. The maximal entanglement point between impurity and local host spin increases as the impurity coupling strength increases. So the impurity coupling strength and local transverse field on the impurity can control position of critical point and maximal entanglement point.