Towards quantum key distribution with noisy communication sources

TL;DR

This paper explores a quantum key distribution protocol using displaced thermal states, demonstrating its feasibility with common microwave communication equipment and analyzing its robustness against losses.

Contribution

It introduces a thermal state QKD protocol independent of displacement and assesses its security and practicality with existing broadcasting technology.

Findings

QKD can be performed using displaced thermal states similar to microwave communication signals.

The protocol remains secure despite losses, with advantage distillation needed at high loss levels.

Security is maintained even when loss is introduced at multiple points in the system.

Abstract

A beam emitted by a displaced thermal source, incident on a beam splitter, is used as the source in a central broadcast quantum key distribution protocol. These displaced thermal states have parallels to signals produced through phase-shift keying, already commonly used in a variety of microwave-based communications equipment. Here, we analyse a thermal state quantum key distribution protocol for which there is no dependency on displacement. Our analysis suggests the ability to carry out QKD using widely available broadcasting equipment. We also consider the effects of the introduction of loss at several points in the protocol, and find that, while increasing loss in Alice's channel eventually results in advantage distillation being required, security is still maintained.