Reference-frame-independent measurement-device-independent quantum key distribution based on polarization multiplexing

TL;DR

This paper demonstrates a novel polarization multiplexing-based RFI-MDI-QKD protocol that simplifies practical implementation, achieves high clock rates over long distances, and improves key rates under reference frame misalignments.

Contribution

It introduces a new time-bin encoding structure for RFI-MDI-QKD, enabling the distinction of two Bell states and demonstrating the protocol over 50 MHz and 160 km.

Findings

Achieved RFI-MDI-QKD over 50 MHz clock rate and 100+ km distance.

Compared RFI-MDI-QKD with original MDI-QKD, showing robustness against reference frame misalignments.

Implemented four-intensity decoy-state RFI-MDI-QKD with biased bases at 100 km and 120 km.

Abstract

Measurement-device-independent quantum key distribution (MDI-QKD) is proved to be able to eliminate all potential detector side channel attacks. Combining with the reference frame independent (RFI) scheme, the complexity of practical system can be reduced because of the unnecessary alignment for reference frame. Here, based on polarization multiplexing, we propose a time-bin encoding structure, and experimentally demonstrate the RFI-MDI-QKD protocol. Thanks to this, two of the four Bell states can be distinguished, whereas only one is used to generate the secure key in previous RFI-MDI-QKD experiments. As far as we know, this is the first demonstration for RFI-MDI-QKD protocol with clock rate of 50 MHz and distance of more than hundred kilometers between legitimate parties Alice and Bob. In asymptotic case, we experimentally compare RFI-MDI-QKD protocol with the original MDI-QKD protocol at the transmission distance of 160 km, when the different misalignments of the reference frame are deployed. By considering observables and statistical fluctuations jointly, four-intensity decoy-state RFI-MDI-QKD protocol with biased bases is experimentally achieved at the transmission distance of 100km and 120km. The results show the robustness of our scheme, and the key rate of RFI-MDI-QKD can be improved obviously under a large misalignment of the reference frame.