Aiming at the problem that the performance of existing sky-underwater quantum key distribution schemes is difficult to meet the relevant requirements in the environment of naval battle field, a sky-underwater quantum key distribution scheme based on phase matching protocol is proposed. In view of the channel asymmetry in the sky-underwater quantum key distribution scheme, an asymmetric phase matching protocol model is proposed to improve the classical phase matching protocol. The feasibility of sky-underwater quantum key distribution based on phase matching protocol under asymmetric channel conditions is studied by using correlation optimization method. The simulation results show that: Under dry and clean atmospheric conditions, in Jerlov I, II and III water bodies, the limit depth of underwater platforms is 1100m, 180m and 110m, respectively, based on the ability to generate keys. This performance basically meets the requirements of the current underwater platforms for concealability. At the same time, the distance between the air platform and the surface platform can exceed 100km, which has certain practicality. It has certain guiding significance for quantum network deployment.
Aiming at the problem that the performance of existing sky-underwater quantum key distribution schemes is difficult to meet the relevant requirements in the environment of naval battle field, a sky-underwater quantum key distribution scheme based on phase matching protocol is proposed. In view of the channel asymmetry in the sky-underwater quantum key distribution scheme, an asymmetric phase matching protocol model is proposed to improve the classical phase matching protocol. The feasibility of sky-underwater quantum key distribution based on phase matching protocol under asymmetric channel conditions is studied by using correlation optimization method. The simulation results show that: Under dry and clean atmospheric conditions, in Jerlov I, II and III water bodies, the limit depth of underwater platforms is 1100m, 180m and 110m, respectively, based on the ability to generate keys. This performance basically meets the requirements of the current underwater platforms for concealability. At the same time, the distance between the air platform and the surface platform can exceed 100km, which has certain practicality. It has certain guiding significance for quantum network deployment.
The phase-matching protocol is a practical and promising protocol that can surpass the linear key generation rate boundary. However, classical phase-matching quantum key distribution requires the channel attenuation between communicating parties to be symmetric. In practice, channels used are often asymmetric, owing to geographical reasons in a quantum key distribution network. To enhance the practicality of phase-matching, this paper proposes an asymmetric phase-matching protocol based on the classical framework and establishes a relevant mathematical simulation model to study the influence of channel asymmetry on its performance. The simulation results show that channel asymmetry significantly affects the count rate, error rate, gain, and quantum bit error rate (QBER), ultimately, system performance. As the channel attenuation difference increases, the system performance decreases and the rate of decrease accelerates. Key generation becomes impossible when the channel attenuation difference exceeds 4 dB. Although the decoy-state scheme cannot change the system's tolerance to channel attenuation difference, when the channel attenuation difference is large, the increasing of the number of decoy states significantly can improve system performance, with a three-decoy-state phase-matching protocol outperforming a two-decoy-state protocol. Considering the limited data length, the system performance is improved as the data length increases, and the tolerance to channel attenuation differences gradually increases. When the data length exceeds 1012, this improvement does not continue any more. The system cannot break through the boundary of linear key generation rate when the channel attenuation difference is 2 dB and the data length is less than 1012. Comparing with symmetric channels, the system performance improvement is very significant under asymmetric channel conditions as the data length increases.
Considering the ocean water’s optical attenuation and the roughness of the sea surface, we analyze the security of continuous-variable (CV) quantum key distribution (QKD) based air-to-water channel. The effects of the absorption and scattering on the transmittance of underwater quantum channel and the maximum secure transmission distance are studied. Considering the roughness of the sea surface, we simulate the performance bounds of CV QKD with different wind speeds using the Monte Carlo method. The results show that even if the secret key rate gradually reduces as the wind speed increases, the maximum transmission distance will not be affected obviously. Compared to the works regarding short-distance underwater optical communication, our research represents a significant step towards establishing secure communication between air platform and submarine vehicle .
Focusing on the application scenario where the underwater mobile platforms wirelessly access the cabled underwater information networks to achieve communication, an underwater access scheme for measurement-device-independent quantum key distribution is proposed to ensure communication security. Based on the analysis of the optical characteristics of the seawater channel, an underwater access model of measurement-device-independent quantum key distribution is constructed, simulated and analyzed to verify the feasibility and effectiveness of the scheme. The simulation results show that the maximum secure access distance of the scheme (under extreme conditions) can be extended from 147 meters to 230 meters or even 451 meters as the seawater type changes from turbid seawater to moderately turbid seawater to clear seawater. The vacuum + weak decoy state scheme can obtain performance that is very close to this limit. After considering the effect of finite data-set size, the performance of the scheme is reduced, but it can still meet the application requirements of underwater mobile platform access within a certain range. In practical applications, measures such as deploying wired communication buoys at network nodes can be used to further expand the effective access range.
Quantum key distribution (QKD) allows for the establishment of a secret key between two parties, secure against computationally unbounded adversaries. Most experimental and theoretical research in this area, investigates the performance of QKD over fiber or free space channels. A growing body of work, however, has begun to investigate its performance in underwater scenarios. Here, we consider the realistic finite key scenario, and evaluate the simulated performance of two different decoy state protocols. We show that there are certain underwater channels where "simpler" QKD protocols outperform more complex ones. Finally, we also investigate methods to improve QKD performance underwater, specifically looking at classical advantage distillation, which we show can greatly improve the maximal distance supported by QKD underwater.
Considering the irregular air-water interface, incident angle, environmental background light and optical attenuation, the system model of quantum key distribution (QKD) based on air-water channel is built. And the influence of wind speed and incident angle on the error rate of system is discussed. Besides, under different attenuation coefficients, the effect of actual incident angle and environmental background light on system performance is studied. The simulations show that when the descending photon passes through the air-water interface, the raise of wind speed leads to an increase in error rate. Similarly, the enlarging of actual incident angle also causes the growth of error rate and shortens the transmission distance of QKD system. Moreover, since the environmental background light can seriously damage the system performance, the QKD experiment should be conducted on cloudy night. With the maximum error rate on cloudy night, the secure transmission distance in clear seawater can reach 252 m, which obviously meets the need of 100 m diving depth for underwater vehicles. In medium seawater and turbid seawater, they are 42 m and 25 m, respectively. Auxiliary means (such as towing buoys) can be used to extend the transmission distance of QKD. Therefore, the QKD system based on air-water channel is feasible, which has certain reference value to expand QKD applications.
Based on the Seafloor Observation Network, a scheme is proposed for underwater mobile platform to achieve secure communication by achieving quantum key distribution with network nodes and then accessing the backbone network. We construct a mathematical model of underwater quantum key distribution, and verify the feasibility of the underwater quantum key distribution and access scheme through simulation. The simulation results show that the quantum key distribution in clear, mixed and chaotic sea water can reach respectively the maximum secure communication distances of 339m, 56m, and 33m. It has a certain reference for the close-distance confidential communication between underwater mobile platforms and underwater network nodes.