Abstract In this paper, we theoretically and experimentally study the performance of an entanglement-based quantum key distribution (QKD) system using single-photon detectors (SPDs) with poor afterpulse characteristics. We reveal that the afterpulse fraction ( P a ) in an SPD does not impose a bound on the lowest limit of the error rate in sifted keys of an entanglement-based QKD system. Secure secret key sharing is possible even when P a is large, for example, exceeding 100%. The system performance in terms of the final key rate is found to be dominated by the parameter η/(1 + P a ) of the SPD, where η is the detection efficiency. The operation conditions of the SPD should be optimized so as to have the maximal η/(1 + P a ), while retaining sufficiently low dark counts. The experimental results were in good agreement with the theoretical predictions. A visibility of 90%, which is sufficiently high for secure secret key sharing in a QKD protocol, was obtained in twofold interference experiments even by using an SPD with P a exceeding 100%.
Abstract In this paper, we theoretically and experimentally study the performance of an entanglement-based quantum key distribution (QKD) system using single-photon detectors (SPDs) with poor afterpulse characteristics. We reveal that the afterpulse fraction ( P a ) in an SPD does not impose a bound on the lowest limit of the error rate in sifted keys of an entanglement-based QKD system. Secure secret key sharing is possible even when P a is large, for example, exceeding 100%. The system performance in terms of the final key rate is found to be dominated by the parameter η/(1 + P a ) of the SPD, where η is the detection efficiency. The operation conditions of the SPD should be optimized so as to have the maximal η/(1 + P a ), while retaining sufficiently low dark counts. The experimental results were in good agreement with the theoretical predictions. A visibility of 90%, which is sufficiently high for secure secret key sharing in a QKD protocol, was obtained in twofold interference experiments even by using an SPD with P a exceeding 100%.
In this paper, we introduce a new Quantum Key Distribution (QKD) protocol designed to reduce afterpulsing by at least 55%. We provide both theoretical analysis and simulation results for a single-photon QKD system using SPADs that exhibit less-than-ideal afterpulse behavior. Our findings show that the afterpulse probability (P AP ) in SPADs does not set a strict lower limit on the error rate of sifted keys in single-photon QKD systems. The system uses a simplified two-state version of the BB84 protocol, with quantum states encoded in different polarizations over fiber or free-space channels. The protocol ensures that consecutive photons have distinct polarizations. In the enhanced protocol, four detectors measure two polarization bases, yielding four possible detection outcomes. The results demonstrate the practical potential of this approach for both fiber-optic and free-space quantum communication, making it especially suitable for real-world deployment. This work paves the way for developing new protocols in quantum communications. In the new method, by avoiding the transmission of two consecutive photons with the same polarization angle, the security level of the optimal BB84 protocol against attacks will be reduced to that of the B92 protocol. Simulations conducted in MATLAB and OptiSystem, under realistic conditions (1550 nm wavelength, InGaAs SPAD parameters: η = 30%, DCR = 10%, clock rate = 100 MHz), demonstrate a drop in afterpulse probability from 53% to 23.2%. The main advantages of the new protocol method over hardware-based methods are lower cost and no need for extensive hardware modifications. Additionally, using the optimized protocol alongside other methods to reduce afterpulse probability further decreases its occurrence.
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.
The afterpulse effect is an undesirable phenomenon that occurs in single-photon avalanche diodes (SPADs). SPADs are widely employed in quantum key distribution (QKD) systems. As QKD systems advance to support higher data rates, the minimization of afterpulses becomes increasingly critical. In this paper, we introduce new structure for BB84 QKD protocol to reduce afterpulses in QKD systems. The proposed method does not change secure key rate compared to the conventional BB84 protocol. We conduct a theoretical analysis and simulation of the performance of a single-photon-based QKD system utilizing SPADs with suboptimal afterpulse characteristics. Our results indicate that the afterpulse probability (Pa) in SPADs does not impose a strict lower bound on the error rate of sifted keys in single-photon-based QKD systems. The system utilizes a simplified version of the two-bases BB84 protocol, which operates over fiber-optic or free-space channels. In the proposed structure, eight detectors are used to measure four polarization angles, yielding four possible outcomes. The findings emphasize the practicality of this setup for both fiber-based and free-space quantum communication, making it highly suitable for real-world applications. The afterpulse decay is dependent on an exponential function and changes proportionally to the elapsed time, the number of trapped carriers, the carrier lifetime, the field strength, and the temperature. The project team has extensive experience in afterpulse reduction and has published several papers on the subject. Using the idea presented in this paper, by doubling the receiver detectors under the same conditions, the probability of afterpulse occurrence is approximately halved. We are looking to propose new structures and protocols to reduce undesired pulses in single-photon avalanche detectors.
The afterpulse effect is an undesirable phenomenon that occurs in single-photon avalanche diodes (SPADs). SPADs are widely employed in quantum key distribution (QKD) systems. As QKD systems advance to support higher data rates, the minimization of afterpulses becomes increasingly critical. In this paper, we introduce what we believe to be a new structure for the BB84 QKD protocol to reduce afterpulses in QKD systems. The proposed method does not change the secure key rate compared to the conventional BB84 protocol. We conduct a theoretical analysis and simulation of the performance of a single-photon-based QKD system utilizing SPADs with suboptimal afterpulse characteristics. Our results indicate that the afterpulse probability (Pa) in SPADs does not impose a strict lower bound on the error rate of sifted keys in single-photon-based QKD systems. The system utilizes a simplified version of the two-bases BB84 protocol, which operates over fiber-optic or free-space channels. In the proposed structure, eight detectors are used to measure four polarization angles, yielding four possible outcomes. The findings emphasize the practicality of this setup for both fiber-based and free-space quantum communication, making it highly suitable for real-world applications. The afterpulse decay is dependent on an exponential function and changes proportionally to the elapsed time, the number of trapped carriers, the carrier lifetime, the field strength, and the temperature. The project team has extensive experience in afterpulse reduction and has published several papers on the subject. Using the idea presented in this paper, by doubling the receiver detectors under the same conditions, the probability of afterpulse occurrence is approximately halved. We are looking to propose new structures and protocols to reduce undesired pulses in single-photon avalanche detectors.
The afterpulse effect is an undesirable phenomenon that occurs in single-photon avalanche diodes (SPADs). SPADs are widely employed in quantum key distribution (QKD) systems. As QKD systems advance to support higher data rates, the minimization of afterpulses becomes increasingly critical. In this paper, we introduce new structure for BB84 QKD protocol to reduce afterpulses in QKD systems. The proposed method does not change secure key rate compared to the conventional BB84 protocol. We conduct a theoretical analysis and simulation of the performance of a single-photon-based QKD system utilizing SPADs with suboptimal afterpulse characteristics. Our results indicate that the afterpulse probability (Pa) in SPADs does not impose a strict lower bound on the error rate of sifted keys in single-photon-based QKD systems. The system utilizes a simplified version of the two-bases BB84 protocol, which operates over fiber-optic or free-space channels. In the proposed structure, eight detectors are used to measure four polarization angles, yielding four possible outcomes. The findings emphasize the practicality of this setup for both fiber-based and free-space quantum communication, making it highly suitable for real-world applications. The afterpulse decay is dependent on an exponential function and changes proportionally to the elapsed time, the number of trapped carriers, the carrier lifetime, the field strength, and the temperature. The project team has extensive experience in afterpulse reduction and has published several papers on the subject. Using the idea presented in this paper, by doubling the receiver detectors under the same conditions, the probability of afterpulse occurrence is approximately halved. We are looking to propose new structures and protocols to reduce undesired pulses in single-photon avalanche detectors.