Quantum key distribution (QKD) networks can provide unconditional secure communications among many remote users. In real QKD networks, with the dynamic access and quit of nodes, qualities of various user links and the link lengths among different users, such as transmission loss, are different and changing. Customized optimization that aims at various channel environments offers a network performance benefit. In this paper, we propose including the detection efficiency, dark-count probability, and afterpulse rate of the single-photon avalanche photodiode (SPAD) into the parameter optimization by controlling its voltage and temperature to optimize the secure key rates in dynamic QKD networks. The result shows that our method improves the network adaptability to the variation and asymmetry of channel and profits the establishment of QKD networks in a complex channel environment. This method is suitable for arbitrary SPAD-based QKD system and network architecture.
Quantum key distribution (QKD) networks can provide unconditional secure communications among many remote users. In real QKD networks, with the dynamic access and quit of nodes, qualities of various user links and the link lengths among different users, such as transmission loss, are different and changing. Customized optimization that aims at various channel environments offers a network performance benefit. In this paper, we propose including the detection efficiency, dark-count probability, and afterpulse rate of the single-photon avalanche photodiode (SPAD) into the parameter optimization by controlling its voltage and temperature to optimize the secure key rates in dynamic QKD networks. The result shows that our method improves the network adaptability to the variation and asymmetry of channel and profits the establishment of QKD networks in a complex channel environment. This method is suitable for arbitrary SPAD-based QKD system and network architecture.
Abstract The safe exchange of cryptographic keys is made possible by Quantum Key Distribution (QKD), which makes use of the basic ideas of quantum physics. Quantum Bit Error Rate (QBER), key generation rate, and transmission distance are important performance measures in QKD systems. Nevertheless, undesired noise sources that impair system performance, such dark counts and afterpulses, restrict traditional QKD implementations. The Measurement-Device-Independent QKD (MDI-QKD) protocol and Single Photon Avalanche Diodes (SPADs) for single-photon detection are combined in this research to create an improved QKD model. All detector-side-channel weaknesses are naturally eliminated by the MDI-QKD protocol, while SPADs' excellent sensitivity and temporal precision allow for precise noise source detection and characterisation, including dark count and afterpulse rates. When compared to conventional QKD systems, the suggested method performs better when assessed using QBER. According to experimental findings, including SPADs into the MDI-QKD architecture greatly improves the security and effectiveness of quantum communication systems by detecting detector-induced errors.
InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency and dark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thickness, excess bias voltage, and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs.
Single-photon detection concept is the most crucial factor that determines the performance of quantum key distribution (QKD) systems. In this paper, a simulator with time domain visualizers and configurable parameters using continuous time simulation approach is presented for modeling and investigating the performance of single-photon detectors operating in Gieger mode at the wavelength of 830 nm. The widely used C30921S silicon avalanche photodiode was modeled in terms of avalanche pulse, the effect of experiment conditions such as excess voltage, temperature and average photon number on the photon detection efficiency, dark count rate and afterpulse probability. This work shows a general repeatable modeling process for significant performance evaluation. The most remarkable result emerged from the simulated data generated and detected by commercial devices is that the modeling process provides guidance for single-photon detectors design and characterization. The validation and testing results of the single-photon avalanche detectors (SPAD) simulator showed acceptable results with the theoretical and experimental results reported in related references and the device's data sheets.
A Single-Photon Avalanche Diode (SPAD) is a specialized optoelectronic device designed for the detection of single photons. It can discern the presence or absence of photons as well as their reception frequency. A significant challenge associated with SPADs is the generation of unintended pulses, which manifest in two primary categories: Dark Count Rate (DCR) and Afterpulse Probability (PAP). Dark counting refers to the occurrence of output pulses in the absence of photon detection, while afterpulse are undesirable outputs resulting from the trapping of carrier’s post-avalanche event within the detector. These trapped carriers are subsequently accelerated by the activation field applied to the detector, causing another avalanche breakdown known as an afterpulse. Both the afterpulse effect and dark counting are considered detrimental phenomena in SPADs, which are commonly utilized in Quantum Key Distribution (QKD) systems. Quantum Key Distribution is a cryptographic method for securely distributing secret keys, leveraging principles of quantum mechanics. Moreover, this method ensures that an eavesdropper cannot intercept or regenerate photon states. In this study, a novel approach is proposed to detect errors induced by these undesirable pulses in a quantum key distribution system. The proposed method, designed to mitigate the effects of unwanted pulses in QKD using the BB84 protocol, employs two quantum channels for photon transmission and a classical channel for coordination between the communicating parties and filtering the secret key (sifting). This method preserves the secure key rate when compared to the traditional BB84 protocol. The reduction of undesirable pulses in the proposed method is contingent upon factors such as the probability of afterpulse occurrence, dark count events, and the efficiency of the single-photon detector, with the reduction being computed in direct proportion to these parameters.
A Single-Photon Avalanche Diode (SPAD) is a specialized optoelectronic device designed for the detection of single photons. It can discern the presence or absence of photons as well as their reception frequency. A significant challenge associated with SPADs is the generation of unintended pulses, which manifest in two primary categories: Dark Count Rate (DCR) and Afterpulse Probability (PAP). Dark counting refers to the occurrence of output pulses in the absence of photon detection, while afterpulse are undesirable outputs resulting from the trapping of carrier’s post-avalanche event within the detector. These trapped carriers are subsequently accelerated by the activation field applied to the detector, causing another avalanche breakdown known as an afterpulse. Both the afterpulse effect and dark counting are considered detrimental phenomena in SPADs, which are commonly utilized in Quantum Key Distribution (QKD) systems. Quantum Key Distribution is a cryptographic method for securely distributing secret keys, leveraging principles of quantum mechanics. Moreover, this method ensures that an eavesdropper cannot intercept or regenerate photon states. In this study, a novel approach is proposed to detect errors induced by these undesirable pulses in a quantum key distribution system. The proposed method, designed to mitigate the effects of unwanted pulses in QKD using the BB84 protocol, employs two quantum channels for photon transmission and a classical channel for coordination between the communicating parties and filtering the secret key (sifting). This method preserves the secure key rate when compared to the traditional BB84 protocol. The reduction of undesirable pulses in the proposed method is contingent upon factors such as the probability of afterpulse occurrence, dark count events, and the efficiency of the single-photon detector, with the reduction being computed in direct proportion to these parameters.
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.