Reference-frame-independent measurement-device-independent quantum key distribution (RFI-MDI-QKD) can reduce the complexity of practical systems caused by the alignment of the reference frame. Lengthening the transmission distance and improving the system clock rate are essential in practical applications of QKD. Herein, in an asymptotic case, we report the results of RFI-MDI-QKD over a distance of 160 km at a clock rate of 50 MHz. By considering the statistical fluctuation of a finite key, we experimentally implemented a four-intensity decoy-state RFI-MDI-QKD protocol with biased bases at transmission distances of 100 km and 120 km. In addition, we compare the RFI-MDI-QKD protocol with the original MDI-QKD protocol when different misalignments of the reference frame are deployed. The results demonstrate the robustness of our scheme and that the key rate of RFI-MDI-QKD can be improved for a large misalignment of the reference frame.

The reference-frame-independent quantum key distribution (RFI QKD) protocol can reduce the requirements on the alignment of reference frames in practical systems. However, compared with the Bennett-Brassard (BB84) QKD protocol, the main drawback of RFI QKD is that Alice needs to prepare six encoding states in three mutually unbiased bases ($X$, $Y$, and $Z$), and Bob also needs to measure the quantum state in three such bases. Here, we show that the RFI QKD protocol can be secured in a case where Alice sends fewer states. In particular, we find that transmitting three states (two eigenstates of the $Z$ basis and one of the eigenstates of the $X$ basis) is sufficient to obtain comparable secret-key rates and distances covered, even when security against coherent attacks with statistical fluctuations of the finite-key size is considered. Finally, a proof-of-principle experiment based on time-bin encoding is demonstrated to show the feasibility of our scheme, and with the three-state protocol, the experimental complexity is effectively alleviated; in particular, a high-speed phase modulator is no longer required by Alice.

Recently, to bridge the gap between security of Measurement-device-independent quantum key distribution (MDI-QKD) and a high key rate, a novel protocol, the so-called detector-device-independent QKD (DDI-QKD), has been independently proposed by several groups and has attracted great interest. A higher key rate is obtained, since a single photon bell state measurement (BSM) setup is applied to DDI-QKD. Subsequently, Qi has proposed two attacks for this protocol. However, the first attack, in which Bob’s BSM setup is assumed to be completely a “black box”, is easily prevented by using some additional monitoring devices or by specifically characterizing the BSM. The second attack, which combines the blinding attack and the detector wavelength-dependent efficiency, is not explicitly discussed, and its feasibility is not experimentally confirmed. Here, we show that the second attack is not technically viable because of an intrinsically wavelength-dependent property of a realistic beam splitter, which is an essential component in DDI-QKD. Moreover, we propose a feasible attack that combines a well-known attack—detector blinding attack with intrinsic imperfections of single-photon detectors. The experimental measurement and proof-of-principle test results confirm that our attack can allow Eve to get a copy of quantum keys without being detected and that it is feasible with current technology.

Quantum digital signatures (QDSs), which are unforgeable, non-repudiable, and transferable, are widely used in quantum communication networks. Unfortunately, previous protocols have often relied on three-party models for security analysis and experimental verification. As the number of parties increases, the number of quantum links required increases exponentially, undoubtedly leading to high channel losses and cost for multi-party QDSs. This study proposes a multi-party ring QDS scheme that can effectively deal with the issue of redundant quantum links. Furthermore, compared with the previously proposed QDS protocols, our protocol can prevent repudiation attacks without symmetry operation or swap test. Hence, it also can reduce the possibility of forging attacks by eliminating the possibility of forgery using illegal strings.