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 .
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 .
Cross-media and confidentiality are key features of next-generation optical communications. Quantum communication is regarded as a promising new form of secure communication. However, the cross-media transmission of quantum pulses tends to suffer from severe attenuation, which inevitably degrades the security of the whole system. In this paper, we consider the configuration of the continuous-variable quantum key distribution through an air–water cross-media channel that involves the lower-atmospheric channel, the underwater channel, and the air–water interface. We consider the effect of air bubbles in seawater, and the effect of the dynamic air–water interface as well. In particular, dynamic characteristics of light extinction and fluctuations caused by seawater and bubbles have been demonstrated with Monte Carlo (MC) simulations. Based on this MC-based model, we demonstrate the communication viability, and simulation results show that in clear seawater conditions with a wind speed of 5 m/s and a zenith angle of 15°, the receiver is able to achieve an effective secret key rate (10 −4 bits/pulse) even at 9.71 m depth. Smaller zenith angles and lower wind speeds contribute to an increase in the interface secret key rate.
There is a growing interest in the security of underwater communication with the increasing demand for undersea exploration. In view of the complex composition and special optical properties of seawater, this paper deals with a performance analysis for continuous-variable quantum key distribution (CVQKD) over an underwater link. In particular, we focus on analyzing the channel transmittance and detection efficiency based on Monte Carlo simulation for different water types, link distances and transceiver parameters. A comparison between the transmittance obtained by simple Beer’s law and Monte Carlo simulation reveals that the transmittance of underwater link may be severely underestimated in the previous underwater CVQKD research. The effect of the receiver aperture and field of view (FOV) on detection efficiency under different water types is further evaluated based on Monte Carlo. Simulation results show that the transmission distance of the underwater CVQKD system obtained by Monte Carlo simulation in pure sea water, clear ocean water and coastal ocean water is larger than that obtained by Beer’s law, while the key rate of the system in all types of water is smaller than that obtained by Beer’s law because the size and FOV of the receiver aperture are taken into account. By considering the practical system parameters, this paper establishes a comprehensive model for evaluating the security of underwater CVQKD systems with different system configurations.
This paper deals with a channel-parameter estimation for continuous-variable quantum key distribution (CV-QKD) over a satellite-to-submarine link. In particular, we focus on the channel transmittances and the excess noise which are affected by atmospheric turbulence, surface roughness, zenith angle of the satellite, wind speed, submarine depth, etc. The estimation method is based on proposed algorithms and is applied to low-Earth orbits using the Monte Carlo approach. For light at 550 nm with a repetition frequency of 1 MHz, the effects of the estimated parameters on the performance of the CV-QKD system are assessed by a simulation by comparing the secret key bit rate in the daytime and at night. Our results show the feasibility of satellite-to-submarine CV-QKD, providing an unconditionally secure approach to achieve global networks for underwater communications.
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.
Addressing the key technical challenges in air-sea cross-medium quantum communication between aircraft and submarines, this paper focuses on quantifying the link attenuation disparity between the uplink (submarine-to-aircraft) and downlink (aircraft-to-submarine) paths and optimizing system parameters. Using the Monte Carlo (MC) simulation method, a multi-medium transmission model encompassing the atmosphere, the air-sea interface, and seawater was constructed to precisely characterize the absorption and scattering behavior of optical signals in the complex cross-medium environment. Building on these attenuation characteristics, a secret key rate calculation model was derived in conjunction with the Gaussian-modulated coherent state (GMCS) Continuous-Variable Quantum Key Distribution (CV-QKD) protocol. The simulation results analyze the influence pattern of depth on the uplink and downlink key rates and clarify the underlying mechanisms for the attenuation disparity between the two paths. The study verifies that the downlink path possesses superior key rate performance due to weaker scattering and angular divergence effects. Furthermore, the paper investigates the modulating effect of modulation variance on the key rate and determines its optimal range.
Considering the ocean water’s optical attenuation is significantly larger than that of Fiber Channel, we propose an approach to enhance the security of underwater continuous-variable quantum key distribution (CVQKD). In particular, the photon subtraction operation is performed at the emitter to enhance quantum entanglement, thereby improving the underwater transmission performance of the CVQKD. Simulation results show that the photon subtraction operation can effectively improve the performance of CVQKD in terms of underwater transmission distance. We also compare the performance of the proposed protocol in different water qualities, which shows the advantage of our protocol against water deterioration. Therefore, we provide a suitable scheme for establishing secure communication between submarine and submarine vehicles.