Pairwise entanglement in fully connected spin systems and its RPA description

R. ROSSIGNOLI; N. CANOSA; J.M. MATERA

Camerino, Italia

Conferencia; ITALIAN QUANTUM INFORMATION SCIENCE CONFERENCE; 2008

The pairwise entanglement at zero and finite temperature in symmetric systems of n spins fully connected through XYZ  couplings and embedded in a transverse magnetic field is examined.  We consider both the exact evaluation together with that obtained with the static path + RPA and the ensuing mean field + RPA treatments. It is shown that the latter is able to provide an accurate analytic description of the concurrence in large systems for all field values and temperatures, while the SPA+RPA improves MF+RPA in finite systems and critical regions. The limit temperature for pairwise entanglement is also analyzed. Finite size effects and special properties of XXZ systems are as well discussed.