Effect of weak randomness on practical reference-frame-independent measurement-device-independent quantum key distribution

Abstract Reference-frame-independent measurement-device-independent quantum key distribution (RFI-MDI-QKD) is considered one of the most promising protocols, as it can generate secret keys without reference frame alignment and defeat all attacks on the measurement side. A fundamental assumption for the security of RFI-MDI-QKD is that both senders can prepare their quantum states with perfect randomness. However, in practical implementations, this assumption may be violated, primarily due to limitations in the imperfect random numbers and quantum device imperfections. In this work, we investigate the effect of weak randomness on the state preparation in practical decoy-state RFI-MDI-QKD, demonstrating that even a small proportion of weak randomness severely compromises the security of RFI-MDI-QKD. Furthermore, we apply the advantage distillation (AD) method to counteract the performance degradation caused by weak randomness in RFI-MDI-QKD. Simulation results demonstrate that AD can significantly improve both the secret key rate and the maximum transmission distance for practical decoy-state RFI-MDI-QKD under weak randomness conditions. These results represent a critical advance toward the development of secure, long-distance, multi-node quantum communication networks.