Experimental Demonstration of High-Rate Measurement-Device-Independent Quantum Key Distribution over Asymmetric Channels

TLDR

MDI‑QKD eliminates detector side channels and is practical with current technology, yet prior symmetric‑channel implementations suffered severely limited key rates when channel losses were asymmetric. In the first high‑rate experiment over asymmetric channels, a 7‑intensity optimization achieved more than tenfold higher key rates and extended secure distance by 20–50 km, advancing MDI‑QKD toward practical networks with asymmetric losses and dynamic node addition.

Abstract

Measurement-device-independent quantum key distribution (MDI-QKD) can eliminate all detector side channels and it is practical with current technology. Previous implementations of MDI-QKD all used two symmetric channels with similar losses. However, the secret key rate is severely limited when different channels have different losses. Here we report the results of the first high-rate MDI-QKD experiment over asymmetric channels. By using the recent 7-intensity optimization approach, we demonstrate>10×higher key rate than the previous best-known protocols for MDI-QKD in the situation of large channel asymmetry, and extend the secure transmission distance by more than 20-50 km in standard telecom fiber. The results have moved MDI-QKD towards widespread applications in practical network settings, where the channel losses are asymmetric and user nodes could be dynamically added or deleted.