Global thermal entanglement in n-qubit systems

R. ROSSIGNOLI; N. CANOSA

PHYSICAL REVIEW A - ATOMIC, MOLECULAR AND OPTICAL PHYSICS

APS

Lugar: New York; Año: 2005 vol. 72 p. 123351 - 123357

1050-2947

We examine the entanglement of thermal states of n spins interacting through  different types of  XY couplings in the presence of a uniform magnetic field, by  evaluating the negativities of all possible bipartite partitions of the whole  system and of subsystems. We consider both the case where every qubit interacts  with all others and where just nearest neighbors interact in a one-dimensional  chain. Limit temperatures for non-zero negativities are also evaluated and  compared with the mean field critical temperature. It is shown that limit  temperatures of global negativities are strictly independent of the magnetic  field in all  XXZ  models, in spite of the quantum transitions that these  models may exhibit at zero temperature, while in anisotropic models they always  increase for sufficiently large fields. Results also show that these  temperatures are higher than those limiting pairwise entanglement.