High-dimensional quantum key distribution (HD-QKD) offers a promising approach to enhance secret key rates beyond conventional binary-encoded QKD, addressing the growing demand for secure data transmission. However, the practical application of most HD-QKD systems has been hindered by their complexity, as they require the preparation and detection of quantum states in large Hilbert spaces. Here, we design and experimentally realize a directly modulated laser platform for HD-QKD. It operates at a repetition rate of 312.5 MHz, yielding a remarkably simple and scalable architecture. Through which, we achieve a record transmission distance of 250 km for HD-QKD, demonstrating its feasibility for long-distance quantum communication. Furthermore, we witness that the four-dimensional states outperform their two-dimensional counterpart in secret key rate, highlighting the practical advantage of high-dimensional encoding. This simple and scalable approach shows strong potential for chip-scale integration.
@article{arxiv.2603.12819,
title = {A Directly Modulated Laser Platform for High-Dimensional Quantum Key Distribution},
author = {Yang Zhou and Xing-Yu Zhou and Shu-Fan Wu and Qiang Zeng and Zhi-Liang Yuan and Qin Wang},
journal= {arXiv preprint arXiv:2603.12819},
year = {2026}
}