Quantum key distribution (QKD) networks are promising to serve large numbers of users with information-theoretic secure communication. In QKD networks, the detection-safe protocol, termed measurement-device-independent (MDI) QKD, can naturally enhance realistic security by supporting untrusted measurement nodes. However, the environmental disturbances to quantum states degrade the performance of multi-user communication. Here we propose an MDI-QKD networking scheme with robustness against environmental disturbance and adaptability to multi-user access, where more than two users can generate keys simultaneously regardless of aligning reference frames and compensating channel disturbance on polarization. To achieve this, we introduce the reference-frame-independent protocol as well as a polarization-compensation-free method, design a multi-user measurement unit, and combine it with original two-user units. The scheme is experimentally demonstrated for the improvement of network robustness and adaptability in multi-user scenarios, and the time and device costs of disturbance compensation can be saved from O ( N ) to O ( 1 ) for an N-user network.
Quantum key distribution (QKD) networks are promising to serve large numbers of users with information-theoretic secure communication. In QKD networks, the detection-safe protocol, termed measurement-device-independent (MDI) QKD, can naturally enhance realistic security by supporting untrusted measurement nodes. However, the environmental disturbances to quantum states degrade the performance of multi-user communication. Here we propose an MDI-QKD networking scheme with robustness against environmental disturbance and adaptability to multi-user access, where more than two users can generate keys simultaneously regardless of aligning reference frames and compensating channel disturbance on polarization. To achieve this, we introduce the reference-frame-independent protocol as well as a polarization-compensation-free method, design a multi-user measurement unit, and combine it with original two-user units. The scheme is experimentally demonstrated for the improvement of network robustness and adaptability in multi-user scenarios, and the time and device costs of disturbance compensation can be saved from O ( N ) to O ( 1 ) for an N-user network.
Quantum key distribution (QKD) can serve large numbers of users with unconditional secure communication, in which measurement-device-independent (MDI) QKD protocol can conveniently enhance realistic security by eliminating all detector side channels. In multi-user scenarios, MDI-QKD networks should meet the requirements of reliability and robustness. Around the issues, we complete a series of work on performance improvement, low-cost deployment, and robust networking. First is to answer how to change the trusted node to the untrusted node with low cost, here we propose and demonstrate an MDIQKD which is compatible with phase encoding BB84 networks, allowing for economical deployment of MDI-QKD networks and reconciliation between high key rate and high realistic security in the same network. Then we make the MDI networks more robust. We design an MDI-QKD networking scheme for multi-user access where more than two users can generate keys synchronously regardless of aligning reference frames and compensating channel disturbance on polarization. Third, we find a general method to distil secure keys from quantum discord, which is different to the previous entanglement-based frameworks of MDI-QKD, allowing imperfect preparation and measurement of quantum states. The series of work can help the practical application of MDI-QKD networks, and promote the development of quantum networks.
Measurement-device-independent quantum key distribution (MDI QKD) is a promising protocol for removing all detector side channel attacks. However, the variation of reference frames, e.g., polarization and phase reference, would be an acute threat to the performance of MDI systems. Here, based on polarization scrambling units, we demonstrate a reference-frame-independent MDI QKD scheme that is inherently stable against volatile channel conditions; therefore, the final secure key rate will be insensitive to the random disturbances of polarization and the drifts of phase reference. Thus, calibrations of the primary reference frames are intrinsically removed in our scheme, which essentially reduces potential vulnerabilities as well as the resource consumption of the whole system. In addition, a proof-of-principle experiment with an improved fluctuation analysis method is demonstrated to verify the feasibility and advantages of the proposed scheme.
Measurement-device-independent quantum key distribution (MDI QKD) is a substantial step toward practical information-theoretic security for key sharing between remote legitimate users (Alice and Bob). As with other standard device-dependent quantum key distribution protocols, such as BB84, MDI QKD assumes that the reference frames have been shared between Alice and Bob. In practice, a nontrivial alignment procedure is often necessary, which requires system resources and may significantly reduce the secure key generation rate. Here, we propose a phase-coding reference-frame-independent MDI QKD scheme that requires no phase alignment between the interferometers of two distant legitimate parties. As a demonstration, a proof-of-principle experiment using Faraday-Michelson interferometers is presented. The experimental system worked at 1 MHz, and an average secure key rate of 8.309 bps was obtained at a fiber length of 20 km between Alice and Bob. The system can maintain a positive key generation rate without phase compensation under normal conditions. The results exhibit the feasibility of our system for use in mature MDI QKD devices and its value for network scenarios.
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.
Measurement-device-independent quantum key distribution (MDI-QKD) can eliminate detector side channels and prevent all attacks on detectors. The future of MDI-QKD is a quantum network that provides service to many users over untrusted relay nodes. In a real quantum network, the losses of various channels are different and users are added and deleted over time. To adapt to these features, we propose a protocol that allows users to independently choose their optimal intensity settings to compensate for different channel losses. Such a protocol enables a scalable high-rate MDI-QKD network that can easily be applied for channels of different losses and allows users to be dynamically added/deleted at any time without affecting the performance of existing users.
Measurement-device-independent quantum key distribution (MDI QKD) is a crucial step for the quantum Internet, as it removes all detector side channels and enables secure QKD with untrusted nodes. However, MDI QKD faces a significant challenge from polarization alignment, since drift of the state of polarization affects the efficiency of key generation, especially when the quantum states are sent from remote locations. Conventional methods for polarization alignment either require additional resources, such as classical lasers or reference pulses, or interrupt the QKD process, which reduces the efficiency of the system. In this paper, an efficient polarization-alignment method in MDI QKD is proposed that leverages intrinsic events from MDI to directly calculate how to compensate for polarization drift. The proposed method does not require additional resources such as reference pulses, thereby eliminating bandwidth limitations, and it is fast, as it can directly calculate how to correct polarization with a small criterion fluctuation. We also introduce the polarization dimension in addition to the encoding dimension and establish a response-rate model for MDI QKD with additional polarization dimensions. Overall, the proposed method is a resource-efficient solution for polarization drift correction in MDI QKD, which can enhance the practicality and scalability of QKD networks.