1204.2337 (Tomotaka Kuwahara)

General properties of the maximized entanglement of indirectly
interacting two spins    [PDF]

Tomotaka Kuwahara

We investigate the thermal entanglement of indirectly interacting two spins through other spins, that is, two spins at the ends of a spin chain. We maximize it by tuning the local fields on the two spins to obtain the maximized entanglement. We prove that if the two spins are separated by two sites or more, there is a critical temperature above which the maximized entanglement vanishes. We numerically calculate the maximized entanglement in three-spin chains and four-spin chains. We discover that the maximizing local fields on the spins 1 and 2 have asymmetric forms, which implies that the asymmetry of the two spins essentially contributes to the entanglement enhancement. In the three-spin chains, we explain this enhancement due to the asymmetry qualitatively and quantitatively in terms of the magnons. In \textit{XX} and \textit{XY} four-spin chains, we find that the critical temperature shows qualitatively different behavior depending on the conservation of the angular momentum in the \textit{z} direction.

View original: http://arxiv.org/abs/1204.2337