Emaranhamento e Desigualdade de Bell no Modelo XXZ

Abstract

For many years it was believed that entanglement and violation of the Bell inequalities were the same peculiar aspect of Quantum Mechanics: non-locality. Nowadays, it is known that this equivalence is not complete, being true only for pure states; in other words, there are entangled mixed states that do not violate the Bell inequalities. Thus it is interesting to analyze properties of states which exhibit such difference, in order to better understand it. Here we present such a study of the connection between entanglement and violation of the Bell inequalities in Quantum Phase Transitions. More pecifically, we analyze this relation for two particles in an infinity one-dimensional spin-12 chain described by the XXZ model. We show that the two particles do not violate the Bell-CHSH inequality for any value of anisotropy, even in regions where they are entangled. Therefore, the entanglement that is relevant in Quantum Phase Transitions is not a trivial one , since it is not revealed by the Bell-CHSH inequality. We also demonstrate that the study of the Bell-CHSH inequality can indicate not only the first order phase transition as the infinity order one, while the fundamental energy per particle and the concurrence can only indicate the first order phase transition.