Abstract Mode-pairing quantum key distribution (MP-QKD) is an excellent scheme that can exceed the repeaterless rate-transmittance bound without complex phase locking. Nevertheless, MP-QKD usually needs to ensure that the communication distances of the two channels are equal. To address the problem, the asymmetric MP-QKD protocol is proposed. In this paper, we enhance the performance of the asymmetric MP-QKD protocol based on the advantage distillation (AD) method without modifying the quantum process. The simulation results show that the AD method can extend the communication distance by about 70 km in the case of asymmetry. And we observe that as the misalignment error increases, the AD method further increases the expandable communication distance. Our work can further enhance the robustness and promote the practical application of the asymmetric MP-QKD.
Abstract Mode-pairing quantum key distribution (MP-QKD) is an excellent scheme that can exceed the repeaterless rate-transmittance bound without complex phase locking. Nevertheless, MP-QKD usually needs to ensure that the communication distances of the two channels are equal. To address the problem, the asymmetric MP-QKD protocol is proposed. In this paper, we enhance the performance of the asymmetric MP-QKD protocol based on the advantage distillation (AD) method without modifying the quantum process. The simulation results show that the AD method can extend the communication distance by about 70 km in the case of asymmetry. And we observe that as the misalignment error increases, the AD method further increases the expandable communication distance. Our work can further enhance the robustness and promote the practical application of the asymmetric MP-QKD.
Abstract The advantage distillation (AD) technology has been proven to effectively improve the secret key rate and the communication distance of quantum key distribution (QKD). The mode-pairing quantum key distribution (MP-QKD) protocol can overcome a fundamental physical limit, known as the Pirandola–Laurenza–Ottaviani–Banchi bound, without requiring global phase-locking. In this work, we propose a method based on multi-step AD to further enhance the performance of MP-QKD. The simulation results show that, compared to one-step AD, multi-step AD achieves better performance in long-distance scenarios and can tolerate a higher quantum bit error rate. Specifically, when the difference between the communication distances from Alice and Bob to Charlie is 25 km, 50 km and 75 km, and the corresponding transmission distance exceeds 523 km, 512 km and 496 km, respectively, the secret key rate achieved by multi-step AD surpasses that of one-step AD. Our findings indicate that the proposed method can effectively promote the application of MP-QKD in scenarios with high loss and high error rate.
Mode-pairing quantum key distribution (MP-QKD) is an easy-to-implement scheme that transcends the Pirandola-Laurenza-Ottaviani-Banchi bound without using quantum repeaters. In this paper, we present an improvement of the performance of MP-QKD using an advantage distillation method. The simulation results demonstrate that the proposed scheme extends the transmission distance significantly with a channel loss exceeding 7.6 dB. Moreover, the scheme tolerates a maximum quantum bit error rate of 8.9%, which is nearly twice that of the original MP-QKD. In particular, as the system misalignment error increases, the expandable distance of the proposed scheme also increases. The proposed system is expected to promote the practical implementation of MP-QKD in a wide range of applications, particularly in scenarios involving high channel losses and system errors.
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 mode pairing quantum key distribution (MP-QKD) protocol has attracted considerable attention for its capability to ensure high secure key rates over long distances without requiring global phase locking. However, ensuring symmetric channels for the MP-QKD protocol is challenging in practical quantum communication networks. Previous studies on the asymmetric MP-QKD protocol have relied on ideal decoy state assumptions and infinite-key analysis, which are unattainable for real-world deployment. In this paper, we conduct a security analysis of the asymmetric MP-QKD protocol with the finite-key analysis, where we discard the previously impractical assumptions made in the decoy state method. Combined with statistical fluctuation analysis, we globally optimized the 10 independent parameters in the asymmetric MP-QKD protocol by employing our modified particle swarm optimization. Through further analysis, the simulation results demonstrate that our work achieves improved secure key rates and transmission distances compared to the strategy with additional attenuation. We further investigate the relationship between the intensities and probabilities of signal, decoy, and vacuum states with transmission distance, facilitating their more efficient deployment in future quantum networks.
Mode-pairing quantum key distribution (MP-QKD) is advantageous for long-distance secure communication, leveraging its simple implementation and quadratic scaling capacity. The post-measurement pairing in MP-QKD alleviates the photon-coincidence demands, which are essential for surpassing the fundamental limit to the key-rate transmission. In this work, we propose an improved decoy-state MP-QKD protocol featuring a flexible and efficient pairing strategy. We prove the security of the proposed scheme by presenting an entanglement model for decoy-state MP-QKD. The simulation results show that the secret key rate (SKR) can be enhanced among all distances. Notably, compared with the original scheme [Nature Communication13, 3903 (2022)10.1038/s41467-022-31534-7], the improvement of SKR is greater than 65% within 375 km in the asymptotic case and greater than 50% within 400 km in the finite case. And the achievable distance can be extended in the finite case, especially with a small block length. The simulation results demonstrate the high efficiency of the proposed scheme, which is expected to promote the practical applicability of MP-QKD. Furthermore, the entanglement model could provide a theoretical framework for further security and performance analysis of decoy-state MP-QKD.