Non-Interfering quantum key distribution (NI-QKD) is a novel QKD protocol which can surpass the limit of secure key capacity, which utilizes the characteristics of noninterference between orthogonal polarization states to obtain high key rates without interference. However, its practical application will be limited by the use of weak coherent source (WCS), which has a higher ratio of vacuum state pulses. To overcome the limitation of WCSs, we propose a NI-QKD protocol by using heralded pair coherent source (HNI-QKD), where the response of the right detector and the response of both detectors are defined as the effective events. The HNI-QKD can break the PLOB bound, the key generation performance has been improved by the advantage of the lower ratio of vacuum state pulses in HPCS. Compared to the NI-QKD protocol by using WCS, the HNI-QKD protocol can increase key generation rate and improve the secure transmission distance.
Non-Interfering quantum key distribution (NI-QKD) is a novel QKD protocol which can surpass the limit of secure key capacity, which utilizes the characteristics of noninterference between orthogonal polarization states to obtain high key rates without interference. However, its practical application will be limited by the use of weak coherent source (WCS), which has a higher ratio of vacuum state pulses. To overcome the limitation of WCSs, we propose a NI-QKD protocol by using heralded pair coherent source (HNI-QKD), where the response of the right detector and the response of both detectors are defined as the effective events. The HNI-QKD can break the PLOB bound, the key generation performance has been improved by the advantage of the lower ratio of vacuum state pulses in HPCS. Compared to the NI-QKD protocol by using WCS, the HNI-QKD protocol can increase key generation rate and improve the secure transmission distance.
Abstract A mode-pairing quantum key distribution based on heralded pair-coherent source with passive decoy-states is proposed, named HPCS-PDS-MP-QKD protocol, where the light sources at Alice and Bob sides are changed to heralded pair-coherent sources, and devices designed to implement passive decoy states are included at the transmitter sides to generate the decoy state pulses in the decoy-state window passively. With the defined efficient events and the designed pairing strategy, the key bits and bases can be obtained by data post-processing. Numerical simulation results verify the feasibility of the proposed protocol. The results show that the proposed protocol can exceed PLOB when the pairing interval setting is greater than 103, and the transmission distance exceeds 200 km. When the key transmission distance reaches 300 km and the maximum pairing interval is equivalent to 1, its performance is improved by nearly 1.8 times compared to the original MP-QKD protocol with a weak coherent source (WCS-MP-QKD), and by 6.8 times higher than that of WCS-MP-QKD with passive decoy states (WCS-PDS-MP-QKD). Meanwhile, the key transmission distance can reach 480 km, and surpasses the WCS-PDS-MP-QKD protocol by nearly 40 km. When the total pulse length is greater than 1011, the key generation rate is almost equal to that of infinite pulses. It is a promising QKD protocol that breaks the PLOB bound without requiring phase tracking and locking, has a longer transmission distance and a higher key generation rate, and eliminates the potential of side channel attack.
Mode-pairing quantum key distribution (MP-QKD) is a promising protocol immune to detector side-channel attacks and capable of breaking the repeaterless PLOB bound without global phase locking. Existing MP-QKD protocols employ weak coherent sources (WCSs) with a low probability of single-photon emission, hindering MP-QKD's performance improvement. We propose a new, to the best of our knowledge, MP-QKD protocol using the heralded single-photon source (HSPS) to significantly reduce the vacuum emission probability and increase the single-photon emission rate. Compared with the original WCS-MP-QKD protocol, this protocol has three advantages. First, its maximum transmission distance is extended from 488 km to 560 km. Second, the key rates at 100, 200, 300, and 400 km are 4.4 to 7.4 times those of the original protocol. Third, it does not change the original architecture of MP-QKD and is easy to implement experimentally. This HSPS-MP-QKD protocol has application potential in future metropolitan area QKD networks.
The security of quantum key distribution (QKD) is based on the basic principles of quantum mechanics, and therefore has unconditional security in theory. In existing quantum key distribution systems, weakly coherent sources (WCSs) are often used as light sources due to a high probability of vacuum pulses in these sources, resulting in limited transmission distances. Besides, there inevitably exist equipment defects in actual QKD systems, such as certain defects in phase modulators and intensity modulators, which lead to distinguishability of quantum states in higher dimensions and result in side-channel vulnerabilities. An eavesdropper can carry out corresponding attacks, thereby threatening the actual security of QKD systems. To overcome the above limitations, we propose an improved protocol on quantum key distribution based on monitoring heralded single-photon sources. Due to the simultaneity of parametric down-conversion photon pairs, we can accurately predict the arrival of one photon by measuring the arrival time of another photon. Through this way, we can greatly reduce the probability of vacuum states in the signal light, and increase the longest transmission distance of the QKD system. Moreover, a light source monitoring module is inserted into the sender’s side. By randomly selecting a certain period of time through the source monitoring module to measure the Hong-Ou-Mandel interference between the signal light and the idle light , we can estimate the side-channel information leakage of the source and then obtain the key generation rate. Compared with the QKD protocol based on monitoring weak coherent sources, our present protocol can give a better performance in either the transmission distance or the key generation rate, especially when the interference error is large. In addition, in principle, our present protocol can also be extended to other quantum key distribution protocols, such as the measurement-device-independent protocols, to further improve the security and practicability of QKD systems. Therefore, our present work can provide valuable references for realizing the large-scale application of quantum communication networks in the near future.
Increasing the bit rate and transmission distance of quantum key distribution (QKD) without quantum repeaters is a formidable challenge, which is limited by the secret-key capacity (SKC). Fortunately, phase-matching QKD (PM-QKD) can overcome this limitation by matching the phase of two coherent states and encoding the key information into the common phase. But the probability of the weak coherent source (WCS) sending a single photon is small, so studying the QKD of different signal sources is one of the effective ways to improve the performance of the QKD protocol. The single-photon-added coherent state (SPACS) has a high probability of sending single photons and is closer to an ideal single-photon source than WCS. We have done simulations combining the advantages of the source with the advantages of PM-QKD. Numerical simulations show that the SPACS-PM-QKD protocol also has the ability to break the SKC, and using the SPACS is better in terms of communication distance and key rate compared to WCS.
Based on the heralded pair-coherent states sources, the Vacuum+Weak decoy state protocol focused on BB84 is presented. Combining the passive decoy state method and the active decoy state method, we use the triggered and nontriggered components to estimate the fraction of single-photon counts and quantum bit-error rate of single-photon and to generate the secure key. From the simulation results of the final key rate over the distance, which shows that our method improve the QKD performance and obtain higher key generation rate than that of the active decoy states method.
Quantum cryptography has a strong security that classical cryptography cannot match, and quantum key distribution (QKD) is the most important method of quantum cryptography. Reference-frame-independent measurement-device-independent QKD (RFI-MDI-QKD) protocol can avoid the drift of the reference frame and all side channels of measurement devices. However, RFI MDI-QKD usually employs a weak coherent state (WCS) as the light source, which limits the transmission distance of secure keys. Here, by using heralded single-photon sources, we investigate an improved decoy-state RFI-MDI-QKD scheme. We perform numerical simulations for the scheme under different scenarios, such as considering the finite size and different drift angles. Compared with the scheme with WCS, our scheme can significantly improve the transmission distance of RFI-MDI-QKD.