Measurement-device-independent quantum key distribution (MDI-QKD) eliminates detector side-channel attacks by relocating all measurements to an untrusted intermediate node. However, its practical implementation critically relies on picosecond-level temporal synchronization between spatially separated users. In this work, we present a physically motivated autonomous synchronization algorithm for fiber-based MDI-QKD networks that does not require auxiliary optical channels or shared clock references. The method exploits round-trip optical pulse propagation and statistical signal detection in the presence of Gaussian noise. We derive analytical expressions for false-alarm probabilities, quantify detection reliability, and demonstrate through numerical modeling that synchronization accuracy better than 10~ps is achievable for channel lengths up to 100~km with realistic optical power levels. The proposed approach improves the scalability and robustness of MDI-QKD architectures and is directly applicable to metropolitan and backbone quantum networks.
Measurement-device-independent quantum key distribution (MDI-QKD) eliminates detector side-channel attacks by relocating all measurements to an untrusted intermediate node. However, its practical implementation critically relies on picosecond-level temporal synchronization between spatially separated users. In this work, we present a physically motivated autonomous synchronization algorithm for fiber-based MDI-QKD networks that does not require auxiliary optical channels or shared clock references. The method exploits round-trip optical pulse propagation and statistical signal detection in the presence of Gaussian noise. We derive analytical expressions for false-alarm probabilities, quantify detection reliability, and demonstrate through numerical modeling that synchronization accuracy better than 10ps is achievable for channel lengths up to 100km with realistic optical power levels. The proposed approach improves the scalability and robustness of MDI-QKD architectures and is directly applicable to metropolitan and backbone quantum networks.
Measurement-device-independent quantum key distribution (MDI-QKD) eliminates detector side-channel attacks by relocating all measurements to an untrusted intermediate node. However, its practical implementation critically relies on picosecond-level temporal synchronization between spatially separated users. In this work, we present a physically motivated autonomous synchronization algorithm for fiber-based MDI-QKD networks that does not require auxiliary optical channels or shared clock references. The method exploits round-trip optical pulse propagation and statistical signal detection in the presence of Gaussian noise. We derive analytical expressions for false-alarm probabilities, quantify detection reliability, and demonstrate through numerical modeling that synchronization accuracy better than 10 ps is achievable for channel lengths up to 100 km with realistic optical power levels. The proposed approach improves the scalability and robustness of MDI-QKD architectures and is directly applicable to metropolitan and backbone quantum networks.
Measurement-device-independent quantum key distribution (MDI-QKD) eliminates detector side-channel attacks by relocating all measurements to an untrusted intermediate node. However, its practical implementation critically relies on picosecond-level temporal synchronization between spatially separated users. In this work, we present a physically motivated autonomous synchronization algorithm for fiber-based MDI-QKD networks that does not require auxiliary optical channels or shared clock references. The method exploits round-trip optical pulse propagation and statistical signal detection in the presence of Gaussian noise. We derive analytical expressions for false-alarm probabilities, quantify detection reliability, and demonstrate through numerical modeling that synchronization accuracy better than 10 ps is achievable for channel lengths up to 100 km with realistic optical power levels. The proposed approach improves the scalability and robustness of MDI-QKD architectures and is directly applicable to metropolitan and backbone quantum networks.
Measurement-device-independent quantum key distribution (MDI-QKD) eliminates detector side-channel attacks by relocating all measurements to an untrusted intermediate node. However, its practical implementation critically relies on picosecond-level temporal synchronization between spatially separated users. In this work, we present a physically motivated autonomous synchronization algorithm for fiber-based MDI-QKD networks that does not require auxiliary optical channels or shared clock references. The method exploits round-trip optical pulse propagation and statistical signal detection in the presence of Gaussian noise. We derive analytical expressions for false-alarm probabilities, quantify detection reliability, and demonstrate through numerical modeling that a scanning resolution of 10 ps is achievable for channel lengths of up to 100 km with realistic optical power levels. The actual timing accuracy is limited by detector, source, and electronic jitter and is not quantified in this work. The proposed approach improves the scalability and robustness of MDI-QKD architectures and is directly applicable to metropolitan and backbone quantum networks.
Purpose of the study: develop and evaluate an algorithm for synchronizing stations in a quantum key distribution system with an untrusted intermediate node. Methods of research: probability distribution, statistical analysis, Gaussian distribution. Results: the importance of high-precision synchronization is substantiated, an autonomous optical signal search algorithm is proposed and analyzed, and simulation results are presented. The issue of autonomous synchronization of two remote stations in a quantum key distribution system is considered. The station connection scheme is a topology with an untrusted intermediate node. An algorithm for synchronizing stations with an untrusted intermediate node is proposed, which does not require an additional optical communication channel. A unique feature of the algorithm is that the stations independently determine the distance to the beam splitter in the untrusted node with an accuracy of tens of picoseconds. Simulation modeling of the developed algorithm is conducted, and the results are presented. This paper describes the operating principle of the MDI quantum key distribution protocol within a mixed-topology quantum network and proposes a scheme for interaction between several legitimate users of the quantum network and a single untrusted node. Scientific novelty: an algorithm for synchronizing optical signals in quantum networks for MDI-QKD is proposed, characterized by its autonomous implementation. Simulation results for the algorithm are presented, and data are obtained that improve the efficiency of engineering calculations when designing a synchronization system.
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.
Measurement-device-independent quantum key distribution (MDI-QKD), based on two-photon interference, is immune to all attacks against the detection system and allows a QKD network with untrusted relays. Since the MDI-QKD protocol was proposed, fiber-based implementations aimed at longer distance, higher key rates, and network verification have been rapidly developed. However, owing to the effect of atmospheric turbulence, MDI-QKD over a free-space channel remains experimentally challenging. Herein, by developing a robust adaptive optics system, high-precision time synchronization and frequency locking between independent photon sources located far apart, we realized the first free-space MDI-QKD over a 19.2-km urban atmospheric channel, which well exceeds the effective atmospheric thickness. Our experiment takes the first step toward satellite-based MDI-QKD. Moreover, the technology developed herein opens the way to quantum experiments in free space involving long-distance interference of independent single photons.