Abstract Quantum key distribution (QKD) has reached a global scale by utilizing the powerful scheme in free space scenes with a more flexible transmission. Unfortunately, the practical applicability of free-space QKD is usually curtailed by the fact that the atmospheric turbulence unavoidably destructs the quality of the quantum signal, which limits its maximum transmission distance. Here we propose an attenuation scheme for the Gaussian modulated coherent state QKD, in which a quantum catalysis operation acts as a noiseless attenuation process to regulate the potentially deteriorated quantum signal, enabling the improvement of maximal transmission distance. Compared with the original protocol, the QC-assisted attenuation presents a promotion of maximum transmission distance. In particular, we find that the zero-photon catalysis-based protocol performs better than the QC-based one. Numerical analysis shows that the QC-assisted attenuation can reduce the amount of information obtained by eavesdroppers, whereas it has a relatively light impact on mutual information. It provides a promising solution towards tackling the atmospheric turbulence in practice.
Abstract Quantum key distribution (QKD) has reached a global scale by utilizing the powerful scheme in free space scenes with a more flexible transmission. Unfortunately, the practical applicability of free-space QKD is usually curtailed by the fact that the atmospheric turbulence unavoidably destructs the quality of the quantum signal, which limits its maximum transmission distance. Here we propose an attenuation scheme for the Gaussian modulated coherent state QKD, in which a quantum catalysis operation acts as a noiseless attenuation process to regulate the potentially deteriorated quantum signal, enabling the improvement of maximal transmission distance. Compared with the original protocol, the QC-assisted attenuation presents a promotion of maximum transmission distance. In particular, we find that the zero-photon catalysis-based protocol performs better than the QC-based one. Numerical analysis shows that the QC-assisted attenuation can reduce the amount of information obtained by eavesdroppers, whereas it has a relatively light impact on mutual information. It provides a promising solution towards tackling the atmospheric turbulence in practice.
Satellite-based quantum key distribution (QKD) has lately received considerable attention due to its potential to establish a secure global network. Associated with its application is a turbulent atmosphere that sets a notable restriction to the transmission efficiency, which is especially challenging for ground-to-satellite uplink scenarios. Here, we propose a novel noiseless attenuation (NA) scheme involving a zero-photon catalysis operation for source preparation to improve the performance of continuous-variable (CV) QKD over uplink. Numerical analysis shows that the NA-based CV-QKD, under attenuation optimization, outperforms the traditional CV-QKD, which is embodied in extending the allowable zenith angle while improving the effective communication time. Attributing to characteristics of the attenuation optimization, we find that the NA-involved source preparation improves the security bound by relatively reducing the amount of information available to eavesdroppers. Taking the finite-size effect into account, we achieve a tighter bond of security, which is more practical compared with the asymptotic limit.
Compared with discrete variable quantum key distribution (DVQKD), continuous variable (CV) QKD has high security bit rate and other advantages, which, however, are slightly insufficient in secure transmission distance. In addition, the application of quantum catalysis has significantly improved the performance of Gaussian modulated (GM) CVQKD, especially in secure transmission distance. Recently, the application of quantum catalysis has significantly improved the performance of GM-CVQKD. However, whether it can be used to improve the performance of discrete modulated (DM) CVQKD protocol is still ambiguous. Therefore, a scheme of DM CVQKD protocol based on quantum catalysis is proposed in this paper to further improve the performance of the proposed protocol in terms of secure key rate, secure transmission distance and maximum tolerable noise. Our results show that under the same parameters, when the transmittance T introduced by quantum catalysis is optimized, the proposed scheme can effectively further improve the performance of QKD system compared with the original four-state modulation CVQKD scheme. In particular, when the tolerable excess noise is 0.002, the use of quantum catalysis can break the safe communication distance of 300 km with a key rate of 10–8 bits/pulse. However, if this noise is too large, the improvement in the effect of quantum catalysis on protocol performance will be restrained. In addition, in order to highlight the advantages of the use of quantum catalysis, the ultimate limit PLOB (Pirandola-Laurenza-Ottaviani-Banchi) bound of point-to-point quantum communication is given in this paper. The simulation results indicate that although neither the original scheme nor the proposed scheme can break the bound, compared with the former, the latter can be close to the boundary in long-distance transmission. These results provide theoretical basis for achieving the ultimate goal of global quantum security communication.
Quantum catalysis is a feasible approach to increase the performance of continuous-variable quantum key distribution (CVQKD), involving the special zero-photon catalysis (ZPC) operation. However, in the practical point of view, the improvement effect of this operation will be limited by the imperfection of the photon detector. In this paper, we show that the ZPC operation at the sender can be simulated by a post-selection method without implementing it in practical devices. While performing this virtual version of ZPC in CVQKD, we can not only reach the ideal case of its practical implementation with minimal hardware requirement, but also keep the benefit of Gaussian security proofs. Based on Gaussian modulated coherent state protocols with achievable parameters, we enhance the security of the proposed scheme from the asymptotical case to the finite-size scenario and composable framework. Simulation results show that similar to the asymptotical case, both the maximal transmission distance and the tolerable excess noise of virtual ZPC-involved CVQKD outperform the original scheme and the scheme using virtual photon subtraction while considering finite-size effect and composable security. In addition, the virtual ZPC-involved CVQKD can tolerate a higher imperfection of the detector, enabling its practical implementation of the CVQKD system with state-of-the-art technology.
Abstract Discrete modulation can make up for the shortage of transmission distance in measurement-device-independent continuous-variable quantum key distribution (MDI-CVQKD), providing a unique advantage against all side-channel attacks but also creating a challenge for further performance improvement. Here we suggest a quantum catalysis (QC) approach for enhancing the performance of the discrete-modulated (DM) MDI-CVQKD in terms of the achievable secret key rate and lengthening the maximal transmission distance. The numerical simulation results show that the QC-based MDI-CVQKD with discrete modulation, involving a zero-photon catalysis (ZPC) operation, can not only obtain a higher secret key rate than the original DM protocol, but also contribute to a reasonable increase of the corresponding optimal variance. As for the extreme asymmetric and symmetric cases, the secret key rate and maximal transmission distance of the ZPC-involved DM MDI-CVQKD system can be further improved under the same parameters. This approach enables the system to tolerate lower reconciliation efficiency, which may provide excellent potential for practical implementations with state-of-art technology.
Quantum photon-catalysis operations can be utilized for improving the performance of continuous-variable quantum key distribution (CVQKD) systems. Motivated by characteristics of quantum photon-catalysis operations that can be implemented by the existing technologies, we consider the performance improvement of self-referenced (SR) CVQKD involving zero-photon catalysis operation. We find that the zero-photon catalysis can be regarded as a noiseless attenuation, and the numerical simulations show that the zero-photon catalysis (ZPC)-based SR-CVQKD scheme outperforms the original SR-CVQKD scheme. In addition, to highlight the advantage of applying zero-photon catalysis operation into SR-CVQKD systems, we make a comparison about the performances between the ZPC-based SR-CVQKD scheme and the previous single-photon subtraction (SPS)-based SR-CVQKD scheme. Numerical simulations show that the ZPC-based SR-CVQKD is superior to the single-photon subtraction case with respect to the transmission distance and the tolerable excess noise. Especially, the ZPC-based SR-CVQKD allows the lower quantum detection efficiency and the higher electronic noise to achieve the same performance. These results show that the proposed protocol is expected to provide theoretical reference for the practical application of SR-CVQKD in metropolitan areas.
Quantum catalysis has been proven to be effective in improving the performance of Gaussian modulation continuous variable quantum key distribution (CVQKD) protocols, significantly enhancing secure transmission distances. However, there is currently a lack of research on utilizing quantum catalysis to improve the performance of four-state modulation protocols. This paper focuses on enhancing the one-dimensional four-state modulation continuous variable quantum key distribution protocol using quantum catalysis. While Gaussian modulation CVQKD protocols offer the advantage of higher secure key rates, their secure transmission distances are limited. On the other hand, discrete modulation protocols exhibit better performance in terms of transmission distances. Additionally, to further simplify the protocol complexity, we adopt a one-dimensional modulation approach. This not only reduces the implementation cost and complexity but also enhances the robustness, secure key rates, and transmission distances of the protocol.