# High-Dimensional and Multi-Intensity One-Photon-Interference Quantum Secure Direct Communication

## TL;DR

This paper introduces a new quantum communication protocol that improves security and transmission distance using high-dimensional encoding.

## Contribution

The novel protocol uses high-dimensional phase encoding in one-photon interference to enhance secrecy and extend transmission distances.

## Key findings

- The protocol achieves a maximum communication distance of 494 km, 13% longer than two-dimensional protocols.
- It doubles the transmission length of traditional quantum secure direct communication protocols.
- Numerical simulations confirm improved secrecy capacity and resistance to quantum threats.

## Abstract

As a novel paradigm in quantum communication, quantum secure direct communication (QSDC) enables secure, reliable, and deterministic information transmission, leveraging the principles of quantum mechanics. One-photon-interference QSDC is particularly attractive because it mitigates the vulnerabilities in measurement devices while extending transmission distances. In this paper, we propose a high-dimensional one-photon-interference QSDC protocol that exploits the advantages of high-dimensional encoding in the phase of weak coherent pluses to further enhance transmission distances and improve secrecy channel capacity. The security of this protocol is analyzed using quantum wiretap channel theory, and its resistance to common quantum threats is discussed. Numerical simulations demonstrate that our protocol outperforms its predecessor in terms of its secrecy capacity and extends the maximum communication distance achievable up to 494 km, which is over 13% longer than the two-dimensional case, effectively doubling the transmission length of traditional protocols. These improvements highlight the protocol’s potential for use in quantum communication applications in this era of frequent data breaches and information leaks.