# Photonic Engineering for CV-QKD over Earth-Satellite Channels

## TL;DR

This paper explores how photonic engineering, specifically photon-added and photon-subtracted states, can enhance the secret key rate in satellite-based quantum key distribution systems, considering various deployment complexities and atmospheric conditions.

## Contribution

It introduces a comparative analysis of engineered photonic states for CV-QKD over Earth-satellite channels, identifying optimal states for different deployment scenarios.

## Key findings

- Photon-added states improve key rates under certain conditions.
- Atmospheric turbulence significantly impacts key rate predictions.
- Feedback-based deployment strategies outperform simple models.

## Abstract

Quantum Key Distribution (QKD) via satellite offers up the possibility of unconditionally secure communications on a global scale. Increasing the secret key rate in such systems, via photonic engineering at the source, is a topic of much ongoing research. In this work we investigate the use of photon-added states and photon-subtracted states, derived from two mode squeezed vacuum states, as examples of such photonic engineering. Specifically, we determine which engineered-photonic state provides for better QKD performance when implemented over channels connecting terrestrial receivers with Low-Earth-Orbit satellites. We quantify the impact the number of photons that are added or subtracted has, and highlight the role played by the adopted model for atmospheric turbulence and loss on the predicted key rates. Our results are presented in terms of the complexity of deployment used, with the simplest deployments ignoring any estimate of the channel, and the more sophisticated deployments involving a feedback loop that is used to optimize the key rate for each channel estimation. The optimal quantum state is identified for each deployment scenario investigated.