Optimizing the qudit dimensions of position-momentum entangled photons for QKD

TL;DR

This paper introduces an optimization method for high-dimensional quantum key distribution using position-momentum entangled photons, enhancing secure key rates by optimizing qudit dimensions and measurement strategies in a passive optical setup.

Contribution

It presents a novel optimization scheme for qudit dimensions in high-dimensional QKD, maximizing secure key rate through a passive optical measurement setup and strategic discarding of ambiguous events.

Findings

Optimized qudit dimension increases secure key rate.

Passive optical setup with a single lens is feasible.

Experimental validation confirms scheme's practicality.

Abstract

We propose an optimization scheme to maximize the secure key rate of a high-dimensional variant of BBM92. We use the position-momentum conjugate bases to encode the higher dimensional qudits, realised in a fully passive optical setup. The setup employs a single lens for the basis measurements and no lossy or slow elements. We optimize the qudit dimension for the protocol by maximizing the number of equiprobable sections (macropixels) of the detected beam while minimizing their overlap error. We show the enhanced key rate by discarding events from the ambiguous border pixels. Our strategy maximizes the overlap between the discarded regions from neighbouring macropixels, thereby globally minimizing the overall loss and error. We calculate the optimal dimension and the secure key rate for certain beam parameters. We experimentally show the feasibility of our scheme. This work paves the way for realistic implementations of high-dimensional device-independent quantum key distribution with enhanced bitrates.