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 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 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.
Underwater quantumkey distribution (QKD) is tough but important formodern underwater communications in an insecure environment. It can guarantee secure underwater communication between submarines and enhance safety for critical network nodes. To enhance the performance of continuous-variable quantumkey distribution (CVQKD) underwater in terms ofmaximal transmission distance and secret key rate as well, we adopt measurement-device-independent (MDI) quantum key distribution with the zero-photon catalysis (ZPC) performed at the emitter of one side, which is the ZPC-based MDI-CVQKD. Numerical simulation shows that the ZPC-involved scheme, which is a Gaussian operation in essence, works better than the single photon subtraction (SPS)-involved scheme in the extreme asymmetric case. We find that the transmission of the ZPC-involved scheme is longer than that of the SPS-involved scheme. In addition, we consider the effects of temperature, salinity and solar elevation angle on the system performance in pure seawater. The maximal transmission distance decreases with the increase of temperature and the decrease of sunlight elevation angle, while it changes little over a broad range of salinity.
The scheme of the self-referenced continuous-variable quantum key distribution (SR CV-QKD) has been experimentally demonstrated. However, because of the finite dynamics of Alice's amplitude modulator, there will be an extra excess noise that is proportional to the amplitude of the reference pulse, while the maximal transmission distance of this scheme is positively correlated with the amplitude of the reference pulse. Therefore, there is a trade-off between the maximal transmission distance and the amplitude of the reference pulse. In this paper, we propose the scheme of SR CV-QKD with virtual photon subtraction, which not only has no need for the use of a high intensity reference pulse to improve the maximal transmission distance, but also has no demand of adding complex physical operations to the original self-referenced scheme. Compared to the original scheme, our simulation results show that a considerable extension of the maximal transmission distance can be obtained when using a weak reference pulse, especially for one-photon subtraction. We also find that our scheme is sensible with the detector's electronic noise at reception. A longer maximal transmission distance can be achieved for lower electronic noise. Moreover, our scheme has a better toleration of excess noise compared to the original self-referenced scheme, which implies the advantage of using virtual photon subtraction to increase the maximal tolerable excess noise for distant users. These results suggest that our scheme can make the SR CV-QKD from the laboratory possible for practical metropolitan area application.
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.
Zero-photon catalysis (ZPC) introduces noiseless attenuation and can be implemented by existing technologies in quantum key distribution (QKD) protocols. In this paper, we present a ZPC-based eight-state measurement-device-independent continuous-variable QKD (MDI-CV-QKD) combined with discrete modulation and reverse reconciliation. This ZPC-involved eight-state protocol shows better efficiency in terms of optimal modulation variances, secret key rates, transmission distances, tolerable excess noises, and reconciliation efficiency compared to the eight-state protocol without ZPC, the four-state protocol without ZPC, and the four-state protocol with ZPC, at a low signal-to-noise ratio (SNR).
The non-Gaussian operation can be used not only to enhance and distill the entanglement between Gaussian entangled states, but also to improve the performance of quantum communications. In this paper, we propose a non-Gaussian continuous-variable quantum key distribution (CVQKD) by using quantum catalysis (QC), which is an intriguing non-Gaussian operation in essence that can be implemented with current technologies. We perform quantum catalysis on both ends of the Einstein-Podolsky-Rosen pair prepared by a sender, Alice, and find that for the single-photon QC-CVQKD, the bilateral symmetrical quantum catalysis performs better than the single-side quantum catalysis. Attributing to characteristics of an integral within an ordered product of operators, we find that the quantum-catalysis operation can improve the entanglement property of Gaussian entangled states by enhancing the success probability of non-Gaussian operation, leading to the improvement of the QC-CVQKD system. As a comparison, the QC-CVQKD system involving zero-photon and single-photon quantum catalysis outperforms the previous non-Gaussian CVQKD scheme via photon subtraction in terms of a secret key rate, maximal transmission distance, and tolerable excess noise.