The secret key rate attained by a free-space QKD system in the {\em near-field} propagation regime (relevant for 1-10 km range using ≈7 cm radii transmit and receive apertures and 1.55μm transmission center wavelenght) can benefit from the use of multiple spatial modes. A suite of theoretical research in recent years have suggested the use of orbital-angular-momentum (OAM) bearing spatial modes of light to obtain this improvement in rate. We show that most of the aforesaid rate improvement in the near field afforded by spatial-mode multiplexing can be realized by a simple-to-build overlapping Gaussian beam array (OGBA) and a pixelated detector array. With the current state-of-the-art in OAM-mode-sorting efficiencies, the key-rate performance of our OGBA architecture could come very close to, if not exceed, that of a system employing OAM modes, but at a fraction of the cost.
@article{arxiv.1604.08582,
title = {Quantum Key Distribution Using Multiple Gaussian Focused Beams},
author = {Boulat A. Bash and Nivedita Chandrasekaran and Jeffrey H. Shapiro and Saikat Guha},
journal= {arXiv preprint arXiv:1604.08582},
year = {2016}
}