Multipartite Entanglement at Finite Temperature

TL;DR

This paper explores how quantum and thermal fluctuations affect multipartite entanglement near quantum critical points, revealing universal behaviors and robustness of entanglement at finite temperatures in various spin systems.

Contribution

It introduces a universal phase diagram of quantum Fisher information at quantum phase transitions, linking it to thermal robustness of multipartite entanglement.

Findings

Quantum Fisher information exhibits characteristic scaling laws with temperature.

Topological systems maintain large multipartite entanglement at finite temperature.

Multipartite entanglement reaches the Heisenberg limit in topological phases.

Abstract

The interplay of quantum and thermal fluctuations in the vicinity of a quantum critical point characterizes the physics of strongly correlated systems. Here we investigate this interplay from a quantum information perspective presenting the universal phase diagram of the quantum Fisher information at a quantum phase transition. Different regions in the diagram are identified by characteristic scaling laws of the quantum Fisher information with respect to temperature. This feature has immediate consequences on the thermal robustness of quantum coherence and multipartite entanglement. We support the theoretical predictions with the analysis of paradigmatic spin systems showing symmetry-breaking quantum phase transitions and free-fermion models characterized by topological phases. In particular we show that topological systems are characterized by the survival of large multipartite entanglement, reaching the Heisenberg limit at finite temperature.