Quantum correlations in spin chains at finite temperatures and quantum phase transitions

TL;DR

This paper investigates quantum correlations in an infinite Heisenberg spin chain at finite temperatures, revealing that quantum discord uniquely signals quantum phase transitions even when thermal effects are present.

Contribution

It demonstrates that quantum discord can detect quantum phase transitions at finite temperatures in the Heisenberg model, unlike entanglement and other thermodynamic measures.

Findings

Quantum discord signals QPTs at finite T

Entanglement does not reliably indicate QPTs at finite T

Quantum correlations persist and reveal critical points

Abstract

We compute the quantum correlation (quantum discord (QD)) and the entanglement (EoF) between nearest neighbor qubits (spin-1/2) in an infinite chain described by the Heisenberg model (XXZ Hamiltonian) at finite temperatures. The chain is in the thermodynamic limit and thermalized with a reservoir at temperature T (canonical ensemble). We show that QD, in contrast to EoF and other thermodynamic quantities, spotlight the critical points associated to quantum phase transitions (QPT) for this model even at finite T. This remarkable property of QD may have important implications for experimental characterization of QPTs when one is unable to reach temperatures below which a QPT can be seen.