Quantum discord in a spin system with symmetry breaking

TL;DR

This paper investigates quantum discord in the quantum XY model, revealing universal features of quantum correlations across phase transitions, symmetry breaking, and finite temperatures, with implications for understanding collective quantum phenomena.

Contribution

It provides a detailed analysis of quantum discord behavior in the XY model, highlighting anomalies at phase transitions and factorization points, and explores universal scaling near quantum criticality.

Findings

Quantum discord shows anomalies at phase transitions and factorization points.

Q exhibits universal scaling behavior near quantum critical points.

Thermal correlations display a non-trivial pattern due to factorization.

Abstract

We analyze the quantum discord Q throughout the low-temperature phase diagram of the quantum XY model in transverse field. We first focus on the T=0 order-disorder quantum phase transition both in the symmetric ground state and in the symmetry broken one. Besides it, we highlight how Q displays clear anomalies also at a non critical value of the control parameter inside the ordered phase, where the ground state is completely factorized. We evidence how the phenomenon is in fact of collective nature and displays universal features. We also study Q at finite temperature. We show that, close to the quantum phase transition, Q exhibits quantum-classical crossover of the system with universal scaling behavior. We evidence a non trivial pattern of thermal correlations resulting from the factorization phenomenon.