Odd-even effect of quantum discord and quantum phase transitions in the S=1/2 spin ladder with ring exchange

TL;DR

This paper investigates quantum correlations in a spin ladder with ring exchange, revealing an odd-even effect in quantum discord that signals phase boundaries, challenging traditional indicators of quantum phase transitions.

Contribution

It uncovers a novel odd-even effect of quantum discord in a spin ladder system, providing a new method to detect phase boundaries beyond quantum entanglement.

Findings

Quantum discord shows an odd-even effect in certain phases.

Quantum discord can indicate phase boundaries.

Quantum entanglement does not signal critical points.

Abstract

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.