Simultaneous variances of Pauli strings, weighted independence numbers, and a new kind of perfection of graphs

TL;DR

This paper explores the connection between graph theory and quantum information through the study of a special class of graphs called $ ext{ extbackslash hbar}$-perfect, revealing applications in entanglement detection, quantum algorithms, and ground state energy estimation.

Contribution

It introduces the class of $ ext{ extbackslash hbar}$-perfect graphs, extending perfect and $h$-perfect graphs, and demonstrates their applications in quantum information processing and graph theory.

Findings

$ ext{ extbackslash hbar}$-perfect graphs enable efficient entanglement detection.

They provide a link to the complexity of shadow tomography.

Approximate Hamilton encoding of independence number scales logarithmically with vertices.

Abstract

A set of Pauli stings is well characterized by the graph that encodes its commutatitivity structure, i.e., by its frustration graph. This graph provides a natural interface between graph theory and quantum information, which we explore in this work. We investigate all aspects of this interface for a special class of graphs that bears tight connections between the groundstate structures of a spin systems and topological structure of a graph. We call this class $\hbar$-perfect, as it extends the class of perfect and $h$-perfect graphs. Having an $\hbar$-perfect graph opens up several applications: we find efficient schemes for entanglement detection, a connection to the complexity of shadow tomography, tight uncertainty relations and a construction for computing good lower on bounds ground state energies. Conversely this also induces quantum algorithms for computing the independence number. Albeit those algorithms do not immediately promise an advantage in runtime, we show that an approximate Hamilton encoding of the independence number can be achieved with an amount of qubits that typically scales logarithmically in the number of vertices. We also we also determine the behavior of $\hbar$-perfectness under basic graph operations and evaluate their prevalence among all graphs.