Quantum discord in the ground state of spin chains

TL;DR

This paper reviews how quantum discord, a measure of quantum correlations, behaves in the ground states of one-dimensional spin chains, especially near quantum phase transitions and factorization points.

Contribution

It provides a comprehensive overview of recent advances in quantifying quantum correlations using discord in spin chains, highlighting its long-range nature and relation to phase transitions.

Findings

Quantum discord is long-ranged near critical points.

Discord reveals nontrivial classical states at factorization points.

Quantum discord can identify quantum critical points.

Abstract

The ground state of a quantum spin chain is a natural playground for investigating correlations. Nevertheless, not all correlations are genuinely of quantum nature. Here we review the recent progress to quantify the 'quantumness' of the correlations throughout the phase diagram of quantum spin systems. Focusing to one spatial dimension, we discuss the behavior of quantum discord close to quantum phase transitions. In contrast to the two-spin entanglement, pairwise discord is effectively long-ranged in critical regimes. Besides the features of quantum phase transitions, quantum discord is especially feasible to explore the factorization phenomenon, giving rise to nontrivial ground classical states in quantum systems. The effects of spontaneous symmetry breaking are also discussed as well as the identification of quantum critical points through correlation witnesses.