Quantum key distribution (QKD) enables information-theoretically secure key establishment, yet its practical performance strongly depends on the behavior of singlephoton detectors. In high-speed systems, afterpulsing effect and dead time can distort detection statistics and cause substantial overestimation of the secure key rate if not properly modeled. To address this issue, we construct a$625-\text{MHz}$BB84-QKD system based on a silica planar-lightwave-circuit asymmetric MachZehnder interferometer chips, incorporate a dependency-modelbased description of detector afterpulse and dead time into the theoretical analysis. This model provides corrected estimations of gain and error rates that more accurately reflect the real detection process. Experimental results show that the system achieves secure key rate of 30.47 kbps at 18 dB channel loss. The strong agreement between the corrected model and measured data confirms that it effectively avoids key-rate overestimation and reliably predicts system performance under practical conditions. The demonstrated on-chip encoding-decoding architecture and refined detector modeling together highlight a promising route toward compact, stable, and high-speed QKD systems, offering valuable guidance for future metropolitan and large-scale quantum communication networks.
Quantum key distribution (QKD) enables information-theoretically secure key establishment, yet its practical performance strongly depends on the behavior of singlephoton detectors. In high-speed systems, afterpulsing effect and dead time can distort detection statistics and cause substantial overestimation of the secure key rate if not properly modeled. To address this issue, we construct a625−MHzBB84-QKD system based on a silica planar-lightwave-circuit asymmetric MachZehnder interferometer chips, incorporate a dependency-modelbased description of detector afterpulse and dead time into the theoretical analysis. This model provides corrected estimations of gain and error rates that more accurately reflect the real detection process. Experimental results show that the system achieves secure key rate of 30.47 kbps at 18 dB channel loss. The strong agreement between the corrected model and measured data confirms that it effectively avoids key-rate overestimation and reliably predicts system performance under practical conditions. The demonstrated on-chip encoding-decoding architecture and refined detector modeling together highlight a promising route toward compact, stable, and high-speed QKD systems, offering valuable guidance for future metropolitan and large-scale quantum communication networks.
Photonics integrated circuits provide a stable, compact and robust platform for the implementation of quantum key distribution (QKD), which can generate information-theoretic secure keys between distant parties. Here, we present a high-speed QKD tests with silica planar lightwave circuits based asymmetric Mach-Zehnder interferometer modules. To further enhance system performance and reduce system complexity, we employ the advantage distillation (AD) algorithm alongside the one-decoy method. The AD algorithm can effectively extract strongly correlated bit pairs from weakly correlated bit pairs, thereby significantly improving the key rate over long distances, where traditional post-processing methods fail to generate keys. With a clock rate of 625 MHz, our system achieves composable secret key rates of 3.32 Mbps at 2 dB loss and 1.85 kbps at 18 dB loss, respectively. These results represent the first experimental validation of AD algorithm, and pave the way for the development of QKD networks with photonic integration.
Quantum key distribution (QKD) has been extensively studied for practical applications. Advantage distillation (AD) represents a key technique to extract highly correlated bit pairs from weakly correlated ones, thus improving QKD protocol performance, particularly in large-error scenarios. However, its practical implementation remains under-explored. In this study, the AD is integrated into the three-intensity decoy-state BB84 protocol and its performance is demonstrated on a high-speed phase-encoding platform. The experimental system employs an asymmetric Mach-Zehnder interferometer (AMZI) fabricated on a silicon dioxide optical waveguide chip for phase encoding, which is benefited from its low coupling loss and minimum waveguide transmission loss. Phase-randomized weak coherent pulses, generated by a distributed feedback laser at 625 MHz, are modulated into decoy states of varying intensities. The signals are encoded via an AMZI and attenuated to single-photon levels before transmission. At the receiver, another AMZI demodulates the signals detected by avalanche photodiodes in gated mode. Experiments conducted at 50 km and 105 km demonstrate secure key rates of 104 kbits/s and 59 bits/s, respectively. The results at shorter distances closely match theoretical predictions, while slight deviations at 105 km are attributed to signal attenuation and noise. Despite these challenges, the results obtained at 105 km highlight the effectiveness of AD in enhancing secure key rates in the large-error scenario. This study confirms the potential of AD in extending secure communication range of QKD. By leveraging the high integration and scalability of silicon dioxide photonic chips, the proposed system lays a foundation for large-scale QKD deployment, paving the way for developing advanced protocols and real-world quantum networks.
Abstract Quantum key distribution (QKD) is recognized as an unconditionally secure method of communication encryption, relying solely on the principles of quantum mechanics. A key performance metric for QKD systems is secure key rate (SKR), which is a critical factor for real-world applications. Herein, we report a practical QKD system, equipped with compact gated InGaAs/InP single-photon detectors (SPDs), that can generate a high SKR of 15.2 Mb/s with a channel loss of 2 dB. This exceptional performance stems from the ultra-low afterpulsing probability of the SPDs, which significantly reduces the bit error rate in the QKD system. The typical quantum bit error rate is 1.3%. The results validate the feasibility of an integrated, practical QKD system and offer a reliable solution for the future development of real-world QKD networks.
Abstract Quantum key distribution (QKD) is a method for secure communication that utilizes quantum mechanics principles to distribute cryptographic keys between parties. Integrated photonics offer benefits such as compactness, scalability, energy efficiency and the potential for extensive integration. We have achieved BB84 phase encoding and decoding, time-bin phase QKD, and the coherent one-way (COW) protocol on a planar lightwave circuit (PLC) platform. At the optimal temperature, our chip successfully prepared quantum states, performed decoding and calculated the secure key rate of the time-bin phase-decoding QKD to be 80.46 kbps over a 20 km transmission with a quantum bit error rate (QBER) of 4.23%. The secure key rate of the COW protocol was 18.18 kbps, with a phase error rate of 3.627% and a time error rate of 0.377%. The uniqueness of this technology lies in its combination of high integration and protocol flexibility, providing an innovative solution for the development of future quantum communication networks.
We report the first quantum-key-distribution (QKD) systems capable of delivering sustainable, real-time secure keys continuously at rates exceeding 10 Mb/s. To achieve such rates, we developed high-speed postprocessing modules, achieving maximum data throughputs of 60 MC/s, 55 Mb/s, and 108 Mb/s for standalone operation of sifting, error correction, and privacy amplification modules, respectively. The photonic layer of the QKD systems features high-speed single-photon detectors based on self-differencing InGaAs avalanche photodiodes, phase encoding using an asymmetric Mach-Zehnder interferometer, and active stabilization of the interferometer phase and photon polarization. An efficient variant of the decoy-state BB84 protocol is implemented for the security analysis, with a large dataset size of 108bits selected to mitigate finite-size effects. Over a 2-dB channel, a record secure key rate of 13.72 Mb/s has been achieved averaged over 4.4 days of operation. We confirm the robustness and long-term stability on a second QKD system continuously running for 1 month without any user invention.
In light of the growing widely utilized single-photon avalanche detectors, dead time is inevitable due to the presence of afterpulse. Dead time is a critical factor that influences the count rate and the secret key rate (SKR) of quantum key distribution (QKD). It is particularly significant in time-bin-encoding systems, while prior models fail to accurately estimate the gains. Of note, it introduces correlations between early bins and late bins, hence bits with strong correlation and security risks. Here, we put forward a realistic model that precisely characterizes the response of detectors for time-bin-encoding systems. Our model not only improves the accuracy of gain predictions, showing an excellent match with the Monte Carlo simulation results, but also provides theoretical support for data processing, helping to mitigate security risks. Finally, leveraging our model, we can get a much higher SKR than prior models and further enhance the performance of practical QKD systems by adjusting the detector parameters. Our simulation results demonstrate that our model is essential for the application and deployment of QKD systems in practice.