High-dimensional entanglement is considered to hold great potential for quantum key distribution (QKD) in high-loss and -noise scenarios. To harness its robustness, we construct a source for high-dimensional time-bin entangled photons optimized for high brightness, low complexity, and long-term stability. We certify the generated high-dimensional entanglement with a new witness employing nested Franson interferometry. Finally, we obtain key rates using a novel, noise-resilient QKD protocol. Our flexible evaluation method, centered around discretizations of the time stream, enables the same dataset to be processed while varying parameters such as state dimensionality and time bin length, allowing optimization of performance under given environmental conditions. Our results indicate regions within the accessible parameter space where high key rates per time are achievable for dimensionalities larger than two.
@article{arxiv.2601.07678,
title = {Bright Source of High-Dimensional Temporal Entanglement},
author = {Dorian Schiffer and Robert Kindler and Alexandra Bergmayr-Mann and Florian Kanitschar and Amin Babazadeh and Paul Erker and Marcus Huber and Anton Zeilinger},
journal= {arXiv preprint arXiv:2601.07678},
year = {2026}
}