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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-points driven quantum phase transitions, 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 that differ from the entanglement. The study of the ground-state properties allows us to show that for a whole class of permutation invariant (η-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 η-pair states is maximal, while, for the purely fermionic ground state, it 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. [ABSTRACT FROM AUTHOR]

We consider photon-number entangled states (PNES) and study the degradation of their entanglement in a noisy channel, using different separability criteria and a recently proposed measure of nonGaussianity as key tools. Upon comparing Gaussian and nonGaussian states within the class, we collect some evidence that Gaussian states are maximally robust against noise, i.e. the complete loss of entanglement occurs in maximal time. However, the gap with respect to nonGaussian states is negligible for sufficiently high energy of the states. [ABSTRACT FROM AUTHOR]