Toward feasible long-distance quantum communications systems

Memory-assisted measurement-device-independent quantum key distribution (MA-MDI-QKD) aims to improve the rateversus-distance behavior of QKD systems by using the existing technologies [1]. While quantum repeater systems, as the ultimate solution to long-distance quantum communications, are still too challenging to be implemented, MA-MDIQKD presents a feasible middle step toward the realization of long-distance QKD. Here, we summarize the progress with MA-MDI-QKD and propose two new MA-MDI-QKD schemes, where one relies on single-photon sources (SPSs) and ensemble-based memories, and the other uses nitrogen-vacancy (NV) centers in diamond embedded into cavities. We calculate the secret key rates for both schemes and compare them with conventional no-memory schemes. We show that, by using the state-of-the-art devices, we can potentially beat existing QKD schemes in reach and rate.