Interplay between quantum phase transitions and the behavior of quantum correlations at finite temperatures

TL;DR

This paper reviews how quantum correlations, especially quantum discord at finite temperatures, can effectively characterize quantum phase transitions in spin chains, providing insights into critical points without reaching absolute zero.

Contribution

It demonstrates the utility of thermal quantum discord in identifying quantum phase transitions in infinite spin chains, extending previous small system results.

Findings

Thermal quantum discord signals quantum critical points effectively.

Behavior of quantum discord at finite T reflects phase transition features.

Results apply to infinite spin chain models like XXZ and XY.

Abstract

We review the main results and ideas showing that quantum correlations at finite temperatures (T), in particular quantum discord, are useful tools in characterizing quantum phase transitions that only occur, in principle, at the unattainable absolute zero temperature. We first review some interesting results about the behavior of thermal quantum discord for small spin-1/2 chains and show that they already give us important hints of the infinite chain behavior. We then study in detail and in the thermodynamic limit (infinite chains) the thermal quantum correlations for the XXZ and XY models, where one can clearly appreciate that the behavior of thermal quantum discord at finite T is a useful tool to spotlight the critical point of a quantum phase transition.