1207.2967 (Tomotaka Kuwahara)

General conditions for the generation of long-distance entanglement    [PDF]

Tomotaka Kuwahara

We generally investigate necessary conditions for the generation of the long-distance entanglement of two spins indirectly interacting through a media system. First, we infinitesimally weaken the coupling between each focused spin and the media system in order to generate the long-distance entanglement. We give two necessary conditions for the media system to generate the long-distance entanglement in the weak coupling limit. We prove that the indirect interaction cannot generate the entanglement if it is 'classical.' We also give a necessary condition for the effective fields to satisfy for the generation of the long-distance entanglement. Second, we generate the long-distance entanglement by the use of only external fields. We show that external fields on adjacent spins are necessary in addition to external fields on the focused spins. A specific combination of the external fields creates the situation where the effective coupling between each focused spin and the media system is infinitesimal. Finally, we consider the cases where the coupling strength between each focused spin and the media system is finite. In particular, we show two examples where the external fields on the media system highly enhance the long-distance entanglement.

View original: http://arxiv.org/abs/1207.2967