Impurity entanglement in the J–J2–δ quantum spin chain

The contribution to the entanglement of an impurity attached to one end of a J–J2–δ quantum spin chain (S = 1/2) is studied. Two different measures of the impurity contribution to the entanglement have been proposed: the impurity entanglement entropy Simp and the negativity . The first, Simp, is based on a subtractive procedure where the entanglement entropy in the absence of the impurity is subtracted from results with the impurity present. …