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

TL;DR

This paper investigates quantum discord and classical correlations in the bond-charge Hubbard model, revealing their roles in quantum phase transitions, off-diagonal long-range order, and monogamy violations, thus highlighting their importance in condensed matter physics.

Contribution

It demonstrates how quantum discord and classical correlations can detect quantum phase transitions and relate to off-diagonal long-range order, introducing new insights into quantum correlations beyond entanglement.

Findings

Quantum discord signals quantum phase transitions effectively.

Quantum discord correlates monotonically with off-diagonal long-range order.

Violation of monogamy property of discord observed in certain states.

Abstract

We study the quantum discord (QD) and the classical correlations (CC) in a reference model for strongly correlated electrons, the one-dimensional bond-charge extended Hubbard model. We show that the comparison of QD and CC and of their derivatives in the direct and reciprocal lattice allows one to efficiently inspect the structure of two-point driven quantum phase transitions (QPTs), discriminating those at which off diagonal long range order (ODLRO) is involved. Moreover we observe that QD between pair of sites is a monotonic function of ODLRO, thus establishing a direct relation between the latter and two point quantum correlations different from the entanglement. The study of the ground state properties allows to show that for a whole class of permutation invariant (\eta-pair) states quantum discord can violate the monogamy 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 is finite. From a general perspective, all our results validate the importance of the concepts of QD and CC for the study of critical condensed-matter systems.