Quantum discord and classical correlations in the bond-charge Hubbard model: quantum phase transitions, ODLRO and violation of the monogamy property for discord

摘要

We study the quantum discord (QD) and the classical correlations (CC) in areference model for strongly correlated electrons, the one-dimensionalbond-charge extended Hubbard model. We show that the comparison of QD and CCand of their derivatives in the direct and reciprocal lattice allows one toefficiently inspect the structure of two-point driven quantum phase transitions(QPTs), discriminating those at which off diagonal long range order (ODLRO) isinvolved. Moreover we observe that QD between pair of sites is a monotonicfunction of ODLRO, thus establishing a direct relation between the latter andtwo point quantum correlations different from the entanglement. The study ofthe ground state properties allows to show that for a whole class ofpermutation invariant (\eta-pair) states quantum discord can violate themonogamy property, both in presence and in absence of bipartite entanglement.In the thermodynamic limit, due to the presence of ODLRO, the violation for\eta-pair states is maximal, while for the purely fermionic ground state isfinite. From a general perspective, all our results validate the importance ofthe concepts of QD and CC for the study of critical condensed-matter systems.