Thermal entanglement in fully connected spin systems and its RPA description

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

PHYSICAL REVIEW A - ATOMIC, MOLECULAR AND OPTICAL PHYSICS

APS

Lugar: New York; Año: 2008 vol. 78 p. 123161 - 123168

1050-2947

We examine the thermal pairwise entanglement in a symmetric system of $n$ spins fully connected through anisotropic $XYZ$-type couplings embedded in a transverse magnetic field. We consider both the exact evaluation together with that obtained with the static path + random phase approximation (RPA) and the ensuing mean field + RPA. The latter is shown to provide an accurate analytic description of both the parallel and antiparallel thermal concurrence in large systems. We also analyze the limit temperature for pairwise entanglement, which is shown to increase for large fields and to decrease logarithmically with increasing $n$. Special finite size effects are as well discussed.