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.
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.
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) 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 phase-matching quantum key distribution (PM-QKD), one of the variants of Twin-Field (TF) QKD protocol, was recently proposed to overcome the rate-distance limits of point to point protocol without quantum repeaters. In this paper, we propose a more practical PM-QKD protocol version with four-intensity decoy states and source errors, since neither the infinite decoy states nor the precise control of the light source is available in practice. We present the formulation of the secure key rate of the proposed protocol and analyze the performances of the protocol with and without source errors by numerical simulations.
The transmission loss of photons during quantum key distribution (QKD) process leads to the linear key rate bound for practical QKD systems without quantum repeaters. Phase matching quantum key distribution (PM-QKD) protocol, an novel QKD protocol, can overcome the constraint with a measurement-device-independent structure, while it still requires the light source to be ideal. This assumption is not guaranteed in practice, leading to practical secure issues. In this paper, we propose a modified PM-QKD protocol with a light source monitoring, named PM-QKD-LSM protocol, which can guarantee the security of the system under the non-ideal source condition. The results show that our proposed protocol performs almost the same as the ideal PM-QKD protocol even considering the imperfect factors in practical systems. PM-QKD-LSM protocol has a better performance with source fluctuation, and it is robust in symmetric or asymmetric cases.
Two time-reversal quantum key distribution (QKD) schemes are the quantum entanglement based device-independent (DI)-QKD and measurement-device-independent (MDI)-QKD. The recently proposed twin field (TF)-QKD, also known as phase-matching (PM)-QKD, has improved the key rate bound from O(η) to O[Formula: see text] with η the channel transmittance. In fact, TF-QKD is a kind of MDI-QKD but based on single-photon detection. In this paper, we propose a different PM-QKD based on single-photon entanglement, referred to as single-photon entanglement-based phase-matching (SEPM)-QKD, which can be viewed as a time-reversed version of the TF-QKD. Detection loopholes of the standard Bell test, which often occur in DI-QKD over long transmission distances, are not present in this protocol because the measurement settings and key information are the same quantity which is encoded in the local weak coherent state. We give a security proof of SEPM-QKD and demonstrate in theory that it is secure against all collective attacks and beam-splitting attacks. The simulation results show that the key rate enjoys a bound of O[Formula: see text] with respect to the transmittance. SEPM-QKD not only helps us understand TF-QKD more deeply, but also hints at a feasible approach to eliminate detection loopholes in DI-QKD for long-distance communications.
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.