# Quantum Key Distribution with Displaced Thermal States

## TL;DR

This paper introduces a new quantum key distribution method using displaced thermal states for secure communication.

## Contribution

A novel experimental implementation of thermal-state QKD using displaced thermal states and broadcasting equipment.

## Key findings

- Displaced thermal states enable sharing of thermal source output among multiple parties.
- Key-ready bit strings are generated without specialized equipment.
- Inherent thermal noise facilitates distinct bit string recovery for all parties.

## Abstract

Secret key exchange relies on the creation of correlated signals, serving as the raw resource for secure communication. Thermal states exhibit Hanbury Brown and Twiss correlations, which offer a promising avenue for generating such signals. In this paper, we present an experimental implementation of a central broadcast thermal-state quantum key distribution (QKD) protocol in the microwave region. Our objective is to showcase a straightforward method of QKD utilizing readily available broadcasting equipment. Unlike conventional approaches to thermal-state QKD, we leverage displaced thermal states. These states enable us to share the output of a thermal source among Alice, Bob, and Eve via both waveguide channels and free space. Through measurement and conversion into bit strings, our protocol produces key-ready bit strings without the need for specialized equipment. By harnessing the inherent noise in thermal broadcasts, our setup facilitates the recovery of distinct bit strings by all parties involved.