Blockwise Key Distillation in Satellite-based Quantum Key Distribution

TL;DR

This paper compares traditional and blockwise key distillation strategies in satellite-based quantum key distribution, demonstrating that the blockwise approach can improve key rates by up to 5% and is easily deployable.

Contribution

It introduces a blockwise key distillation method for satellite QKD, showing its advantages over the traditional approach through extensive simulations.

Findings

Blockwise strategy can improve key rate by up to 5%.

Blockwise approach is effective for different environmental conditions.

Implementation requires only modifications in classical post-processing.

Abstract

Free-space satellite communication has significantly lower photon loss than terrestrial communication via optical fibers. Satellite-based quantum key distribution (QKD) leverages this advantage and provides a promising direction in achieving long-distance inter-continental QKD. Satellite channels, however, can be highly dynamic due to various environmental factors and time-of-the-day effects, leading to heterogeneous noises over time. In this paper, we compare two key distillation techniques for satellite-based QKD. One is the traditional {\em non-blockwise} strategy that treats all the signals as a whole; the other is a {\em blockwise} strategy that divides the signals into individual blocks that have similar noise characteristics and processes them independently. Through extensive simulation in a wide range of settings, we show trends in optimal parameter choices and when one strategy provides better key generation rates than the other. Our results show that the blockwise strategy can lead to up to $5\%$ key rate improvement (leading to on average $1.9\times10^{7}$ more key bits per day) when considering two types of blocks, i.e., for nighttime and daytime, respectively. The blockwise strategy only requires changes in the classical post-processing stage of QKD and can be easily deployed in existing satellite systems.