The classical capacity of quantum thermal noise channels to within 1.45 bits

TL;DR

This paper establishes a tight upper bound on the classical capacity of quantum thermal noise channels, showing it is very close to the lower bound achievable with classical states, indicating limited advantage from quantum strategies.

Contribution

The paper provides a tight upper bound on the classical capacity of quantum thermal noise channels within 1.45 bits, demonstrating the limited benefit of quantum techniques for classical communication.

Findings

Upper bound within 1.45 bits of Holevo's lower bound

Classical states like displaced coherent states nearly achieve the capacity

Quantum tricks offer minimal advantage for classical communication

Abstract

We find a tight upper bound for the classical capacity of quantum thermal noise channels that is within $1/\ln 2$ bits of Holevo's lower bound. This lower bound is achievable using unentangled, classical signal states, namely displaced coherent states. Thus, we find that while quantum tricks might offer benefits, when it comes to classical communication they can only help a bit.