Security of high-dimensional quantum key distribution protocols using Franson interferometers

TL;DR

This paper analyzes the security vulnerabilities of high-dimensional quantum key distribution protocols using Franson interferometers, showing single setups are insecure and proposing multi-interferometer configurations as a more promising solution.

Contribution

It demonstrates the insecurity of single Franson interferometer setups and explores how multiple interferometers can enhance security against photon localization attacks.

Findings

Single Franson interferometers are vulnerable to photon localization attacks.

Multiple interferometers improve sensitivity and security.

Using multiple interferometers is a promising approach for practical high-dimensional QKD.

Abstract

Franson interferometers are increasingly being proposed as a means of securing high-dimensional energy-time entanglement-based quantum key distribution (QKD) systems. Heuristic arguments have been proposed that purport to demonstrate the security of these schemes. We show, however, that such systems are vulnerable to attacks that localize the photons to several temporally separate locations. This demonstrates that a single pair of Franson interferometers is not a practical approach to securing high-dimensional energy-time entanglement based QKD. This observations leads us to investigate the security of modified Franson-based-protocols, where Alice and Bob have two or more Franson interferometers. We show that such setups can improve the sensitivity against attacks that localize the photons to multiple temporal locations. While our results do not constituting a full security proof, they do show that a single pair of Franson interferometers is not secure and that multiple such interferometers could be a promising candidate for experimentally realizable high-dimensional QKD.