The singularity of quantum correlations, such as quantum entanglement(QE) and quantum discord(QD), has been widely regarded as a valuable indicator for quantum phase transition(QPT) in low-dimensional quantum systems. In this paper, for a spin ladder system with ring exchange, we find that the singularity of QD (or QE) could not indicate the critical points of the system. Instead, the QD shows a novel odd-even effect in some phases, which can be used to detect the phase boundary points. The size effect is related to the symmetry breaking of the ladder.
@article{arxiv.1304.7362,
title = {Odd-even effect of quantum discord and quantum phase transitions in the S=1/2 spin ladder with ring exchange},
author = {H. L. Huang and Z. Y. Sun and B. Wang},
journal= {arXiv preprint arXiv:1304.7362},
year = {2013}
}