Spotlighting quantum critical points via quantum correlations at finite temperatures

TL;DR

This paper investigates how quantum correlations like entanglement and discord can detect quantum critical points at finite temperatures across various spin models, providing insights for experimental detection of quantum phase transitions.

Contribution

It extends previous work by analyzing multiple models and correlations at finite temperatures, including beyond nearest neighbors, to assess their effectiveness in identifying critical points.

Findings

Quantum discord and entanglement can signal critical points at finite T.

Quantum correlations outperform thermodynamic quantities in some cases.

Second nearest-neighbor correlations provide additional critical point information.

Abstract

We extend the program initiated in [T. Werlang et al., Phys. Rev. Lett. 105, 095702 (2010)] in several directions. Firstly, we investigate how useful quantum correlations, such as entanglement and quantum discord, are in the detection of critical points of quantum phase transitions when the system is at finite temperatures. For that purpose we study several thermalized spin models in the thermodynamic limit, namely, the XXZ model, the XY model, and the Ising model, all of which with an external magnetic field. We compare the ability of quantum discord, entanglement, and some thermodynamic quantities to spotlight the quantum critical points for several different temperatures. Secondly, for some models we go beyond nearest-neighbors and also study the behavior of entanglement and quantum discord for second nearest-neighbors around the critical point at finite temperature. Finally, we furnish a more quantitative description of how good all these quantities are in spotlighting critical points of quantum phase transitions at finite T, bridging the gap between experimental data and those theoretical descriptions solely based on the unattainable absolute zero assumption.