Performance Analysis of Free-space Quantum Key Distribution Using Multiple Spatial Modes

TL;DR

This paper analyzes free-space quantum key distribution using multiple spatial modes, comparing non-orthogonal flat-top focused beams and orthonormal LG modes, highlighting their performance under turbulence and implementation considerations.

Contribution

It introduces an analysis of non-orthogonal flat-top focused beams for QKD, showing their potential advantages over LG modes in turbulent conditions.

Findings

Non-orthogonal flat-top beams can outperform LG modes under turbulence.

Flat-top beams are easier to implement despite a rate penalty.

Turbulence effects vary between mode types, influencing QKD rate.

Abstract

In the diffraction-limited near-field propagation regime, free-space optical quantum key distribution (QKD) systems can employ multiple spatial modes to improve their key rate. Here, we analyze QKD using the non-orthogonal flat-top focused beams. Although they suffer from a rate penalty, their ease of implementation makes them an attractive alternative to the well-studied orthonormal Laguerre-Gauss (LG) modes. Indeed, in the presence of turbulence, the non-orthogonal modes may achieve higher QKD rate than the LG modes.