The passive decoy method, a candidate for high-speed quantum key distribution (QKD), can prepare laser pulses with various photon-number distributions according to the responses of the transmitter's detectors, which usually adopts the single-photon avalanche photodiode (SPAD) in QKD. As an intrinsic characteristic of the SPAD, the afterpulse can introduce random detector responses, however, is regrettably ignored in passive schemes. Here we develop an analytical model for passive schemes in the finite-resource regime to describe the afterpulse effect on the detectors of both transmitter and receiver. The photon-number distributions biased by afterpulses are corrected, which reveals that the secure key rate is significantly overrated when the afterpulse is ignored. Moreover, our model can increase the tolerance of passive decoy source to afterpulse effect as the result shows that the secret key rates are comparable at different afterpulse probability by reoptimization.
The passive decoy method, a candidate for high-speed quantum key distribution (QKD), can prepare laser pulses with various photon-number distributions according to the responses of the transmitter's detectors, which usually adopts the single-photon avalanche photodiode (SPAD) in QKD. As an intrinsic characteristic of the SPAD, the afterpulse can introduce random detector responses, however, is regrettably ignored in passive schemes. Here we develop an analytical model for passive schemes in the finite-resource regime to describe the afterpulse effect on the detectors of both transmitter and receiver. The photon-number distributions biased by afterpulses are corrected, which reveals that the secure key rate is significantly overrated when the afterpulse is ignored. Moreover, our model can increase the tolerance of passive decoy source to afterpulse effect as the result shows that the secret key rates are comparable at different afterpulse probability by reoptimization.
Reference-frame-independent quantum key distribution (RFI-QKD) enables the generation of secure keys when the reference frame suffers from unknown and slow drifting. To combat the potential photon-number-splitting attacks in RFI-QKD, the decoy-state method should be adopted. Generally, the decoy states are prepared by actively modulating different photon numbers of weak coherent pulses, which, however, may leak the side-channel information due to the imperfect modulation. To address this security loophole, we propose to implement the improved RFI-QKD protocol [Opt. Lett.47, 4219 (2022)10.1364/OL.470558], which bounds the eavesdropper's information analytically and is less sensitive to statistical fluctuations, with passive decoy states. By interfering two weak coherent pulses on a beam splitter and then directing one arm of the outputs into the single-photon avalanche detector (SPAD), different photon-number distributions of pulses can be prepared according to the response status of SPAD. To make this scheme more practical, we consider the inevitable afterpulses of the SPADs for both the transmitter and receiver, and construct an afterpulse-compatible analysis model. Simulation results show that our scheme can achieve good performance in practical scenarios.
There is no doubt that measurement-device-independent quantum key distribution (MDI-QKD) is a crucial protocol that is immune to all possible detector side channel attacks. In the preparation phase, a simulation model is usually employed to get a set of optimized parameters, which is utilized for getting a higher secure key rate in reality. With the implementation of high-speed QKD, the afterpulse effect which is an intrinsic characteristic of the single-photon avalanche photodiode is no longer ignorable, this will lead to a great deviation compared with the existing analytical model. Here we develop an afterpulse-compatible MDI-QKD model to get the optimized parameters. Our results indicate that by using our afterpulse-compatible model, we can get a much higher key rate than the prior afterpulse-omitted model. It is significant to take the afterpulse effect into consideration because of the improvement of the system working frequency.
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.
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.