Separability conditions and limit temperatures for entanglement detection in two qubit Heisenberg XYZ models

N. CANOSA; R. ROSSIGNOLI

PHYSICAL REVIEW A - ATOMIC, MOLECULAR AND OPTICAL PHYSICS

APS

Lugar: New York; Año: 2004 vol. 69 p. 523061 - 523067

1050-2947

  We examine the entanglement of general mixed states of a two qubit Heisenberg   XYZ  chain in the presence of a magnetic field, and its detection by means of  different criteria. Both the exact separability conditions and the weaker  conditions implied by the disorder and the von Neumann entropic criteria are  analyzed. The ensuing limit temperatures for entanglement in thermal states of different            XYZ  models are then examined and compared with the limit  temperature of the symmetry-breaking solution in a mean field type  approximation. The latter, though generally lower, can also be higher than the  exact limit temperature for entanglement in certain cases, indicating that  symmetry-breaking does not necessarily entail entanglement. The reentry of  entanglement for increasing temperatures is also discussed.