Entanglement in the Spin-1 AFM Heisenberg Model

The Fisher information is an experimentally accesible mutipartite entanglement witness. It is unqiue from other entanglement witnesses as it allows for the detection of entanglement at finite temperatures. The spin 1 anit-ferromagnetic Heisenberg model exhibits a non-trivial phase with a gapped excitation spectrum. The addition of a uniaxial anisotropy term may drive two quantum phase transitions. Using the Fisher information we examine the bipartite and multipartite entanglement in a finite temperature region region around the isotropic point and as the quantum critical points are approached. We apply the single mode approximation to examine the entangelement properties of the groundstate in the Haldane gap.