RPA approximation and quantum entanglement in translational invariant spin systems

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

Buenos Aires

Congreso; XI Giambiagi Winter School. The Quantum Mechanics of XXI Century: Manipulation of Coherent Atomic Matter; 2009

Departamento de Física J.J. Giambiagi, UBA

In this contribution we discuss the application of the random phase approximation (RPA) to the evaluation of the pairwise entanglement in spin systems with translational invariance, both at zero and finite temperature. The RPA takes into account the small amplitude quantum fluctuations around the mean field. For spin systems with SU(2)-type interactions in a uniform field, the translational invariance allows us to solve the approximation exactly. It is shown that the approach provides an accurate description of the pairwise concurrence for strong fields, for any coupling range. It also correctly predicts the existence of a separability field together with an infinite entanglement range in its vicinity. Its accuracy improves for high connectivity.