Dynamic Entropy Amplification via Random Fiber Gratings for 6.58 Gbit/s Physical‐Layer Key Distribution Over 600 km Link

Physical‐layer secure key distribution leverages shared random entropy sources to enable key agreement between legitimate parties. However, existing SKD schemes face a fundamental trade‐off between key generation rate and distance, constrained by limited entropy bandwidth and degraded utilization efficiency over long hauls. Here, we introduce chaotic entropy sources to improve the key rate and demonstrate a dynamic entropy amplification architecture that enhances the effective entropy bandwidth and long‐haul entropy utilization efficiency by designing environmentally tunable random fiber gratings. This design separately enables correlation synchronization of the broadband entropy sources within the spectrally flat region and performs entropy perturbation and amplification within the corrugated region. The system experimentally achieves a record distribution rate–distance product, yielding a KGR of 6.58 Gb/s over 600 km. This approach overcomes the longstanding limitations of both static fiber entropy sources and complex synchronization schemes, paving the way for physical‐layer security in backbone and transoceanic communication.