A complex network description of thermal quantum states in the Ising spin chain

TL;DR

This paper applies complex network analysis to an Ising spin chain in a transverse magnetic field, revealing how network measures can characterize quantum phases and transitions beyond traditional methods.

Contribution

It introduces a novel approach of using weighted network analysis with various correlation measures to study quantum many-body systems.

Findings

Network measures reflect traits of complex networks in the spin chain

Network structure varies with transverse field and temperature

Distinct network patterns in quantum critical, ordered, and disordered phases

Abstract

We use network analysis to describe and characterize an archetypal quantum system - an Ising spin chain in a transverse magnetic field. We analyze weighted networks for this quantum system, with link weights given by various measures of spin-spin correlations such as the von Neumann and Renyi mutual information, concurrence, and negativity. We analytically calculate the spin-spin correlations in the system at an arbitrary temperature by mapping the Ising spin chain to fermions, as well as numerically calculate the correlations in the ground state using matrix product state methods, and then analyze the resulting networks using a variety of network measures. We demonstrate that the network measures show some traits of complex networks already in this spin chain, arguably the simplest quantum many-body system. The network measures give insight into the phase diagram not easily captured by more typical quantities, such as the order parameter or correlation length. For example, the network structure varies with transverse field and temperature, and the structure in the quantum critical fan is different from the ordered and disordered phases.