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.
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.
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.
Abstract Mode-pairing quantum key distribution (MP-QKD) is a potential protocol that is not only immune to all possible detector side channel attacks, but also breaks the repeaterless rate-transmittance bound without needing global phase locking. Here we analyze the finite-key effect for the MP-QKD protocol with rigorous security proof against general attacks. Moreover, we propose a six-state MP-QKD protocol and analyze its finite-key effect. The results show that the original protocol can break the repeaterless rate-transmittance bound with a typical finite number of pulses in practice. And our six-state protocol can improve the secret key rate significantly in long distance cases.
Abstract Channel loss in long-distance phase-matching quantum key distribution (PM-QKD) amplifies vacuum emissions and dark counts, impairing parameter estimation and limiting secure transmission distance. In this paper, we propose a PM-QKD protocol based on heralded single-photon sources (HSPSs) with local detection. In the key sifting stage, local heralding outcomes are filtered to suppress vacuum-dominated noise and enhance the single-photon fraction of the retained ensemble. A three-intensity decoy-state method is used to estimate the single-photon contribution and bound the phase-error rate. An asymptotic security analysis is provided. Simulation results show that the proposed protocol surpasses the PLOB bound at 316km and achieves a practical key rate of 10−8 at 496km, while the conventional PM-QKD protocol based on weak coherent sources reaches the same key rate only at 439km. These gains are mainly attributed to the vacuum-event filtering strategy, which effectively improves both key-rate performance and transmission distance. Furthermore, our evaluation of a practical threshold detector implementation demonstrates that photon-number-resolving (PNR) detectors are not mandatory to achieve this advantage.
Mode-pairing quantum key distribution (MP-QKD) can surpass the repeaterless rate-transmittance bound (Pirandola-Laurenza-Ottaviani-Banchi bound) without requiring global phase locking, exhibiting remarkable flexibility. However, MP-QKD necessitates equal communication distances in two channels, which is a challenging requirement in practical applications. To address this limitation, we extend the original MP-QKD to asymmetric cases. Our decoy-state estimation confirms that asymmetric channel transmittances and asymmetric intensities do not compromise the security of the protocol. We focus on the pulse-intensity relationship, a key factor for optimizing the performance of asymmetric MP-QKD. Unlike previous asymmetric protocols, the intensities of different bases in asymmetric MP-QKD cannot be decoupled. We introduce an optimal-pulse-intensity method, adaptable to various scenarios, to enhance key rates by calculating ideal pulse intensities. Simulation results in various representative scenarios indicate that our method effectively reduces the impact of asymmetric channel distances on MP-QKD performance, enhancing its practical applicability.
Quantum key distribution (QKD) provides information-theoretic security for communication. The mode-pairing (MP) protocol emerges as a promising solution for long-distance QKD by eliminating the need for a global phase reference while maintaining the repeaterlike rate-loss scaling. Recent implementations have demonstrated its potential, but they either rely on costly ultrastable lasers or struggle with phase fluctuations from commercial lasers, particularly over long distances. As a result, surpassing the repeaterless bound with a practical system remains a challenge. In this work, we demonstrate a practical high-performance MP-QKD system using commercial lasers. To address phase fluctuations, we propose a frequency-tracking scheme based on fast Fourier transformation, enabling us to extend the pairing length to 2 × 10 5 pulses ( 160 μ s ). We propose a model to carefully analyze the phase noise and optimize the system parameters. Our system achieves an optimal secret key rate of 47.8 bit / s over 403 km of standard fiber (76.5 dB loss), exceeding the repeaterless bound by a factor of 2.92. Furthermore, we compare MP-QKD and twin-field QKD under various practical conditions and clarify the distinct application scenarios of the two protocols. These results confirm the feasibility of MP-QKD using cost-effective commercial technologies, paving the way for scalable quantum communication 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.