Quantum key distribution using hBN single-photon emitters at a 40 MHz clock rate

Room-temperature (RT) solid-state quantum emitters are essential for building practical and scalable quantum communication systems, yet their application has been critically hindered by the slow operational speeds of corresponding modulation technologies. In this work, we overcome this key performance bottleneck. We demonstrate a quantum key distribution (QKD) system using a single defect in hexagonal boron nitride (hBN) with dynamic polarization encoding at a 40 MHz clock rate, an order of magnitude faster than previous demonstrations with similar sources. Implementing the B92 protocol, our system yields a secure key rate of 7 kbps in the finite-key regime with a quantum bit error rate of 6.49%, establishing a new performance benchmark for RT single-photon QKD. Furthermore, to chart a path beyond the limits of direct transmission, we present the first quantitative performance analysis of hBN spin-defects as quantum repeater nodes. Overall, our high-speed experimental demonstration, supported by a foundational analysis of the system architecture, suggests that hBN defects represent a promising and technically feasible platform for scalable, quantum communication.