Quantum impurity entanglement

Entanglement in J1–J2, S = 1/2 quantum spin chains with an impurity is studied using analytic methods as well as large scale numerical density matrix renormalization group methods. The entanglement is investigated in terms of the von Neumann entropy, S = −TrρAlogρA, for a subsystem A of size r of the chain. The impurity contribution to the uniform part of the entanglement entropy, Simp, is defined and analysed in detail in both the gapless, …