The Capacity of Quantum Channel with General Signal States

TL;DR

This paper establishes that the capacity of a classical-quantum channel with general (possibly mixed) states equals the maximum entropy bound over all input distributions, extending previous results from pure states to mixed states.

Contribution

It generalizes the known capacity result from pure state channels to channels with arbitrary mixed states, completing the theoretical understanding.

Findings

Capacity equals the maximum of the entropy bound over all input distributions.

Extends previous pure state results to mixed states.

Provides a complete characterization of channel capacity for general states.

Abstract

It is shown that the capacity of a classical-quantum channel with arbitrary (possibly mixed) states equals to the maximum of the entropy bound with respect to all apriori distributions. This completes the recent result of Hausladen, Jozsa, Schumacher, Westmoreland and Wooters, who proved the equality for the pure state channel.