The most important goal of quantum communication is to distribute the encryption key between the transmitter and the receiver. The optimal situation in Quantum Key Distribution (QKD) between transmitter and receiver is to increase the key distribution rate per second, increase the transmission distance, and reduce the error in key distribution. Several protocols used for QKD. The most important of QKD protocols is the BB84. One of the challenges leading to errors in quantum protocols is generating error pulses in single-photon detectors. These pulses caused by the inherent effects of quantum devices. They can cause wrong detection in the receiver. Many measures have been taken in the design and construction of single-photon detectors to reduce this error pulses, but it is not possible to eliminate all of them. Afterpulse and dark counts are two types of unwanted pulses that occur with single-photon detectors. In this paper, a new QKD protocol is proposed. It is an upgrade of the BB84 protocol and can reduce the effects of unwanted pulses such as afterpulse and dark counts in QKD avalanche detectors.
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.
Afterpulsing is a factor limiting the distance over which discrete-variable quantum key distribution systems are secure, and a common feature in single-photon detectors. The relevance of this phenomenon stems from its stochastic, self-interacting nature and the fact that its rate rises with the number of avalanche events, which increases the quantum bit error rate. Here we introduce an effective analytic model, including dead-time and afterpulsing corrections, where afterpulsing correction depends on dead-time value. This model is useful to evaluate the performance of prepare and measure quantum key distribution protocols (standard and decoy versions) that use gated single photon detectors. The model provides an expression to numerically optimize the secret key rate over the full distance range for secure communication, enabling in this way the calculation of quantum bit error rate and secure key rate. In the conventional procedure, the dead-time value is fixed regardless of distance, limiting the distance range of the channel due to remaining afterpulsing effects, which are more relevant at higher operating frequencies. Here we demonstrate that optimizing the dead-time values increases the distance range of the channel to share secret keys.
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.