A simple quantum channel having superadditivity of channel capacity

TL;DR

This paper demonstrates that quantum channels can exhibit superadditivity of capacity even with minimal extension, and proposes a cavity QED implementation for such channels.

Contribution

It shows superadditivity occurs at the third extension of a simple binary quantum channel and suggests a physical cavity QED realization.

Findings

Superadditivity appears at the third extension of the channel.

A cavity QED-based physical implementation is proposed.

Superadditivity can be observed with simple binary channels.

Abstract

When classical information is sent through a quantum channel of nonorthogonal states, there is a possibility that transmittable classical information exceeds a channel capacity in a single use of the initial channel by extending it into multi-product channel. In this paper, it is shown that this remarkable feature of a quantum channel, so-called superadditivity, appears even in as low as the third extended coding of the simplest binary input channel. A physical implementation of this channel is indicated based on cavity QED techniques.