Curator's Take
AI Commentary
This article demonstrates the first practical use of multi‑plane light conversion to demultiplex entangled photons travelling in a few‑mode fiber, turning each guided mode into an independent BBM92 channel while keeping the underlying quantum correlations intact. By achieving sub‑2 % and sub‑7 % QBER on two parallel links, the work shows that space‑division multiplexing can boost key rates without resorting to high‑dimensional encoding, a route that aligns with recent efforts to leverage existing telecom infrastructure for multi‑user quantum networks. The result paves the way toward scalable, fiber‑based quantum internet nodes where several secure keys are generated simultaneously, though further integration and loss mitigation will be needed before deployment in long‑haul links.
— Mark Eatherly
Summary
As quantum key distribution (QKD) progresses from laboratory demonstrations toward practical deployment, quantum communi- cation networks increasingly require higher key rates and the ability to distribute independent secret keys among multiple users and network nodes. In this paper we present a promsing approach with multi-plane light conversion (MPLC) for demultiplexing entangled photons, transmitted through a few-mode fiber (FMF). We experimentally demonstrated a spatially multiplexed BBM92 QKD scheme. The modes are selectively excited through separate single-mode-fibers and subsequently separated by MPLC into distinct output ports. Unlike high-dimensional QKD based on coherent modal superpositions, our approach exploits distinguishable guided modes as parallel channels while preserving the entanglement required for QKD. For the multiplexed links, we obtain quantum bit error rates of $1.9 \pm 0.4\%$ for the channel 1 and $6.8 \pm 0.8\%$ for the channel 2. These results are relevant for scalable quantum-secured networks, space-division-multiplexed QKD systems, multi-user entanglement distribution, and future quantum internet architectures, where parallel quantum channels must be implemented without compromising the quantum correlations required for security.