The quantum dynamic capacity formula of a quantum channel

TL;DR

This paper presents a simplified proof of the quantum dynamic capacity theorem, characterizes the trade-off surface for quantum communication resources, and computes the capacity regions for specific quantum channels.

Contribution

It provides an elementary proof of the quantum dynamic capacity theorem and demonstrates additivity for certain channels, facilitating capacity calculations.

Findings

Simplified proof of the quantum dynamic capacity theorem.

Characterization of the Pareto optimal trade-off surface.

Exact capacity regions for quantum dephasing and erasure channels.

Abstract

The dynamic capacity theorem characterizes the reliable communication rates of a quantum channel when combined with the noiseless resources of classical communication, quantum communication, and entanglement. In prior work, we proved the converse part of this theorem by making contact with many previous results in the quantum Shannon theory literature. In this work, we prove the theorem with an "ab initio" approach, using only the most basic tools in the quantum information theorist's toolkit: the Alicki-Fannes' inequality, the chain rule for quantum mutual information, elementary properties of quantum entropy, and the quantum data processing inequality. The result is a simplified proof of the theorem that should be more accessible to those unfamiliar with the quantum Shannon theory literature. We also demonstrate that the "quantum dynamic capacity formula" characterizes the Pareto optimal trade-off surface for the full dynamic capacity region. Additivity of this formula simplifies the computation of the trade-off surface, and we prove that its additivity holds for the quantum Hadamard channels and the quantum erasure channel. We then determine exact expressions for and plot the dynamic capacity region of the quantum dephasing channel, an example from the Hadamard class, and the quantum erasure channel.