Lower and upper bounds on nonunital qubit channel capacities

TL;DR

This paper establishes bounds on the classical capacity of nonunital qubit channels by leveraging a decomposition technique that relates them to unital channels, filling a gap in quantum information theory.

Contribution

It introduces a method to bound nonunital qubit channel capacities using a decomposition that connects them to well-understood unital channels.

Findings

Derived lower bounds on nonunital qubit channel capacities

Derived upper bounds on nonunital qubit channel capacities

Provides a framework for analyzing nonunital channel capacities

Abstract

Classical capacity of unital qubit channels is well known, whereas that of nonunital qubit channels is not. We find lower and upper bounds on classical capacity of nonunital qubit channels by using a recently developed decomposition technique relating nonunital and unital positive qubit maps.