Classical-Quantum Dual Encoding for Laser Communications in Space

TL;DR

This paper proposes a dual classical-quantum encoding scheme for laser space communications, enhancing security with quantum key distribution without compromising classical data rates, and validates it through detailed atmospheric channel simulations.

Contribution

It introduces a novel simultaneous classical-quantum encoding method for space laser communications that enhances security with a simple, robust quantum layer compatible with existing systems.

Findings

Secure key generation under passive attacks

Quantum security layer does not affect classical data rates

Protocol performs well in atmospheric channel simulations

Abstract

In typical laser communications classical information is encoded by modulating the amplitude of the laser beam and measured via direct detection. We add a layer of security using quantum physics to this standard scheme, applicable to free-space channels. We consider a simultaneous classical-quantum communication scheme where the classical information is encoded in the usual way and the quantum information is encoded as fluctuations of a sub-Poissonian noise-floor. For secret key generation, we consider a continuous-variable quantum key distribution protocol (CVQKD) using a Gaussian ensemble of squeezed states and direct detection. Under the assumption of passive attacks secure key generation and classical communication can proceed simultaneously. Compared with standard CVQKD. which is secure against unrestricted attacks, our added layer of quantum security is simple to implement, robust and does not affect classical data rates. We perform detailed simulations of the performance of the protocol for a free-space atmospheric channel. We analyse security of the CVQKD protocol in the composable finite-size regime.