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.
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.
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.
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.
In recent years, the feasibility of quantum key distribution (QKD) in a water channel has been verified by theory and experiment. Here, we present an experimental investigation of QKD and decoy-state QKD based on the BB84 protocol. The experiment was carried out in a 10 m water tank. The attenuation coefficient of tap water is 0.08/m, which is close to Jerlov Type II seawater. We measured the probability-of-detection matrix of polarization states, and the average fidelity of the four polarization states is up to 98.39%. For the 10 m underwater QKD experiment, 20 MHz optical pulses are generated by modulating the laser diode (LD) and attenuated to an average of 0.1 photons per pulse. The security key rate can reach 563.41 kbits/s and the quantum bit error rate (QBER) is 0.36%. Two decoy states (one of which is the vacuum state) was used in the 10 m underwater decoy-state QKD experiment, and the average QBER of signal state is 0.95%, the security key rate reaches 711.29 kbits/s. According to the parameters of the decoy-state experiment, the maximum secure transmission distance of the underwater decoy-state QKD is predicted to be 19.2 m, while it can be increased to 237.1 m in Jerlov Type I seawater with a lower dark count single photon detector (SPD).
Underwater quantum key distribution (QKD) has potential applications in absolutely secure underwater communication. However, the performance of underwater QKD is limited by the optical elements, background light, and dark counts of the detector. In this paper, we propose a modified formula for the quantum bit error rate (QBER), which takes into account the effect of detector efficiency on the QBER caused by the background light. Then we calculate the QBER of the polarization encoding BB84 protocol in Jerlov-type seawater by analyzing the effect of the background light and optical components in a more realistic situation. Finally, we further analyze the final key rate and the maximum secure communication distance in three propagation modes, i.e., upward, downward, and horizontal modes. We find that secure QKD can be performed in the clearest Jerlov-type seawater at a distance of hundreds of meters, even in the worst downward propagation mode. Specifically, by optimizing the system parameters, it is possible to securely transmit information with a rate of 67 kbits/s at a distance of 100 m in the seawater channel with an attenuation coefficient of 0.03/m at night. For practical underwater QKD, the performance can also be improved by using decoy states. Our results are useful for long-distance underwater quantum communication.
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.
Abstract Simultaneous two-way classical and quantum (STCQ) communication combines both continuous classical coherent optical communication and continuous-variable quantum key distribution (CV-QKD), which eliminates all detection-related imperfections by being measurement-device-independent (MDI). In this paper, we propose a protocol relying on STCQ communication on the oceanic quantum channel, in which the superposition-modulation-based coherent states depend on the information bits of both the secret key and the classical communication ciphertext. We analyse the encoding combination in classical communication and consider the probability distribution transmittance under seawater turbulence with various interference factors. Our numerical simulations of various practical scenarios demonstrate that the proposed protocol can simultaneously enable two-way classical communication and CV-MDI QKD with just a slight performance degradation transmission distance compared to the original CV-MDI QKD scheme. Moreover, the asymmetric situation outperforms the symmetric case in terms of transmission distance and optical modulation variance. We further take into consideration the impact of finite-size effects to illustrate the applicability of the proposed scheme in practical scenarios. The results show the feasibility of the underwater STCQ scheme, which contributes toward developing a global quantum communication network in free space.