Interplays between classical and quantum entanglement-assisted communication scenarios

TL;DR

This paper investigates how entanglement enhances classical and quantum communication in prepare-and-measure scenarios, revealing that higher-dimensional entanglement can be beneficial and not all entangled states are useful resources.

Contribution

It provides a systematic analysis of entanglement-assisted communication, showing equivalence of quantum and classical messages with doubled capacity and the importance of entanglement dimension.

Findings

Quantum messages with entanglement have twice the capacity of classical ones.

Sharing higher-dimensional entangled states is always advantageous.

Unsteerable states do not provide advantages in communication tasks.

Abstract

Prepare-and-measure scenarios, in their many forms, can be seen as the basic building blocks of communication tasks. As such, they can be used to analyze a diversity of classical and quantum protocols -- of which dense coding and random access codes are key examples -- in a unified manner. In particular, the use of entanglement as a resource in prepare-and-measure scenarios have only recently started to be systematically investigated, and many crucial questions remain open. In this work, we explore such scenarios and provide answers to some seminal questions. More specifically, we show that, in scenarios where entanglement is a free resource, quantum messages are equivalent to classical ones with twice the capacity. We also prove that, in such scenarios, it is always advantageous for the parties to share entangled states of dimension greater than the transmitted message. Finally, we show that unsteerable states cannot provide advantages in classical communication tasks, thus proving that not all entangled states are useful resources in these scenarios.