Curator's Take
AI Commentary
This article demonstrates the first entanglement‑based QKD system that can share an 18 km hollow‑core fiber with full‑power classical data traffic, achieving a steady 10.6 kbps secret key rate while supporting a theoretical 2.3 Tbps data channel. By exploiting the ultra‑low nonlinearity of air‑filled cores, the work sidesteps the Raman and four‑wave mixing noise that has capped silica‑core fibers, and its modeling suggests that low‑loss HCFs could push secure key rates above 100 kbps over 200 km. The result is a concrete step toward integrating quantum security into today’s fiber‑optic backbone without sacrificing bandwidth, although commercial deployment will still depend on scaling up low‑loss hollow‑core manufacturing and robust splicing techniques.
— Mark Eatherly
Summary
The coexistence of quantum information and classical signals in a single fiber is essential for future quantum networks that leverage the well-established optical fiber infrastructure. Although multiplexing technologies can separate quantum and classical signals, pure silica core fibers (PSCFs) remain fundamentally limited by the high nonlinearity, which generates substantial Raman scattering and four-wave mixing noise. Hollow-core fibers (HCFs), guiding light predominantly in air, offer an attractive solution with intrinsically ultra-low nonlinearity and strongly suppressed nonlinear noise. In this work, we demonstrate the entanglement-based key coexisting with data over an 18-km HCF link. We achieve time-encoded high-dimensional quantum key distribution (HD-QKD) carrying 0 dBm of bidirectional received power, corresponding to a theoretical data capacity of up to 2.3 Tbps. During 24 hours of continuous operation, an average secret key rate (SKR) of 10.56 kbps is obtained. Theoretical analysis further predicts SKRs above 135 kbps over transmission distances exceeding 200 km using state-of-the-art low-loss HCFs. These results show significantly improved performance compared with PSCF-based systems and highlight the potential of HCFs for scalable quantum-classical coexistence compatible with the architectures of established fiber-optic networks.