The effect of the irregular air-water interface on the performance of the down-link quantum key distribution from the air to the sea is studied. Based on the analysis of the relationship between the incident angle and the quantum bit error rate, the air-water interface model with wind speed is adopted, the influence of the wind speed on the incident angle of the photon is discussed, the relationship between the expected value of quantum bit error rate and the wind speed is deduced. Numerical simulation shows that the quantum bit error rate of the irregular air-water interface is related to the incident angle and the wind speed. If the incident angle is improved, the quantum bit error rate will increase, limiting the incident angle shall not exceed 40°. And the actual incident angle will improve with the wind speed increasing. We find that when the original incident angle is 10° and the wind speed is less than 10m/s, the maximum actual incident angle do not exceed 40°, which is advantageous to the quantum key distribution.
The effect of the irregular air-water interface on the performance of the down-link quantum key distribution from the air to the sea is studied. Based on the analysis of the relationship between the incident angle and the quantum bit error rate, the air-water interface model with wind speed is adopted, the influence of the wind speed on the incident angle of the photon is discussed, the relationship between the expected value of quantum bit error rate and the wind speed is deduced. Numerical simulation shows that the quantum bit error rate of the irregular air-water interface is related to the incident angle and the wind speed. If the incident angle is improved, the quantum bit error rate will increase, limiting the incident angle shall not exceed 40°. And the actual incident angle will improve with the wind speed increasing. We find that when the original incident angle is 10° and the wind speed is less than 10m/s, the maximum actual incident angle do not exceed 40°, which is advantageous to the quantum key distribution.
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.
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.
This paper mainly solves the photon polarization encoding problem of quantum key distribution (QKD) between different media. The influence of the transmission rate of different photon component on quantum bit error rate (QBER) has been quantitatively analyzed, with a practical analysis of QBER of QKD between air and water. Furthermore, we have put forward a single-photon compensation scheme for eliminating such non-ideal BB84 protocol, as well as a more robust and practical dual-photon encoding scheme to offset such interfacial non-unitary noise. This takes an important step towards the air-sea-ground wide area quantum communication in the future.
Quantum communication is brand new way of communication in which quantum entanglement is used to transmit information. It is an interdisciplinary subject combining quantum informatics with modern communication theory. Motivated by the communication requirements for underwater sensor networks, submarines, etc., underwater optical communication has been developing rapidly in recent years due to the ideal information security of quantum communication. However, the research on the performance of underwater quantum communication in sea has not yet been fully developed because of a series of factors such as surge, salinity and seaweed and so on. In this paper, the influence of surge in non-uniform water flow on the underwater quantum communication is studied theoretically and experimentally. Firstly, a new Boussinesq equation with a given flow function is derived based on the horizontal and vertical wave velocity of the free surface to represent the free surface boundary conditions. On the other hand, In view of the nonlinear motion of movement, the complexity of change and the randomness of the distribution, the spectrum is used for numerically calculating the surge. The characteristics of wave motion are described by wave height, period and wavelength. Secondly, the influence of surge on the entanglement of underwater quantum channel is analyzed. It is proved that the wave height of surge and the change of the cycle affect quantum communication due to the destruction of the quantum coherence and the reduction in quantum entanglement degree. Thirdly, the influence of surge motion on the quantum channel capacity is studied. The influence of the relation between the wavelength and the transmission cycle on the quantum channel capacity is simulated. The relationship between the physical characteristics of surge wave and the capacity of depolarized channel is established. Fourthly, the influence of surge motion on error rate in quantum key distribution is studied. The simulation results show that when the sea surface wind speed changes in a range of 0-20.5 m/s, the propagation cycle is increased gradually. The channel entanglement is increased from 0.0012 to 0.8426, and the channel capacity is reduced from 0.8736 to 0.1024. In the key distribution process, the quantum bit error rate increases from 0.1651 to 0.4812. Therefore, in underwater quantum communication, the parameters of the system should be adjusted adaptively according to the varying degree of the surge movement.
Quantum communication at the sea-air interface is an important direction for expanding quantum information networks. However, current research has not sufficiently considered how waves and bubbles at this interface affect quantum communication. The paper develops a system combining the Cox-Munk sea surface wave model with the Hall-Novarini bubble scattering model, using Monte Carlo simulations to model photon propagation in air-sea channels. Based on data for different wind speeds (5–20 m/s) and four water types (pure, clear, coastal, harbor), the study examines how the sea-air interface influences quantum bit error rate (QBER) and received power for quantum communication. Results show that in pure seawater, higher wind speeds decrease the maximum secure communication depth from 63 m to 25 m. In waters with high turbidity, scattering effects dominate, limiting communication depth to within 10 m. This research identifies environmental thresholds for marine quantum channels, offering a theoretical basis and practical guidelines for designing and improving underwater quantum communication systems.