Multiplexing-enhanced device-independent quantum key distribution

The discrepancy between theoretical models and experimental implementations introduces side-channel vulnerabilities that pose the most critical threat to quantum cryptography systems. Device-independent quantum key distribution (DIQKD) enables two legitimate users to achieve secure key sharing using untrusted devices through the violation of Bell inequalities. Despite recent DIQKD demonstrations, achieving high efficiency and long-distance transmission remains a formidable challenge. We introduce a novel multiplexing-enhanced heralding protocol, transforming loss scaling from $O(\eta_L)$ to $O(\sqrt{\eta_L})$, thereby enabling significantly higher secure key rates. Our work achieves a remarkable system-level breakthrough, surpassing the repeaterless bound at long distances and marks a substantial advancement toward practical DIQKD implementation.