Bell inequality and nonlocality in a two-dimensional mixed spin systems

TL;DR

This study investigates how Bell inequality and nonlocality reveal phase transitions and quantum correlations in a two-dimensional mixed spin system, showing unique thermal effects and phases beyond entanglement.

Contribution

It demonstrates Bell inequality as a detector for both quantum and thermal phase transitions in an exactly solvable 2D spin model, revealing novel thermal enhancement of nonlocality.

Findings

Bell inequality detects quantum and thermal phase transitions.

Nonlocality is enhanced by thermal fluctuations in the antiferromagnetic phase.

Quantum correlations in the ferromagnetic phase are distinct from entanglement and nonlocality.

Abstract

In this paper, we use Bell inequality and nonlocality to study the bipartite correlation in an exactly soluble two-dimensional mixed spin system. Bell inequality turns out to be a valuable detector for phase transitions in this model. It can detect not only the quantum phase transition, but also the thermal phase transitions, of the system. The property of bipartite correlation in the system is also analyzed. In the quantum anti-ferromagnetic phase, the Bell inequality is violated thus nonlocality is present. It is interesting that the nonlocality is enhanced by thermal fluctuation, and similar results have not been observed in anti-ferromagnetic phase. In the ferromagnetic phase, the quantum correlation turns out to be very novel, which cannot be captured by entanglement or nonlocality.