Enhancement of nearest-neighbor entanglement in one-dimensional disordered systems

The pairwise quantum entanglement between sites in disordered electronic one-dimensional systems (rings) is studied. We focus on the effect of diagonal and off-diagonal disorder on the ground-state concurrence C-ij between neighboring and not neighboring sites i,j as a function of electron band filling. In the case of diagonal disorder, increasing the degree of disorder leads to a decrease of the concurrence with respect to the ordered case. However, off-diagonal disorder causes a surprisingly strong enhancement of nearest-neighbor entanglement. This remarkable effect occurs near half filling, where the concurrence becomes up to 15% larger than in the periodic system.