High-dimensional quantum key distribution with resource-efficient detection

TL;DR

This paper demonstrates a high-dimensional quantum key distribution experiment using minimal detection resources, showcasing increased key rates and discussing security implications in urban fiber networks.

Contribution

It presents a novel high-dimensional QKD implementation with only one detector per basis, employing the temporal Talbot effect and comparing security proofs.

Findings

Successful high-dimensional QKD with one detector per basis

Experimental key rates for 2D and 4D encoding demonstrated

Analysis of security issues related to asymmetric detection efficiencies

Abstract

While quantum key distribution (QKD) based on two-dimensional (qubit) encoding is a mature, field-tested technology, its performance is lacking for many cryptographic applications. High-dimensional encoding for QKD enables increased achievable key rates and robustness as compared to the standard qubit-based systems. However, experimental implementations of such systems are more complicated, expensive, and require careful security analysis as they are less common. In this work we present a proof of principle high-dimensional time-phase BB84 QKD experiment using only one single-photon detector per measurement basis. We employ the temporal Talbot effect to detect QKD symbols in the control basis, and show experimentally-obtained simplistic key rates for the two-dimensional and four-dimensional case, including in an urban fiber network. We present a comparison of a simplistic secret key rate obtained from a standard security proof with the one derived from a recently devised proof using a tunable beam splitter to display security issues stemming from asymmetric detection efficiencies in the two bases. Our results contribute to the discussion of the benefits of high-dimensional encoding and highlight the impact of security analysis on the achievable QKD performance.