Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Optics Express

Experimental underwater quantum key distribution

Zhao Feng, Shangbin Li, Zhengyuan Xu

Published Feb 23, 2021• 59 citations
Publisher

Abstract

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).

DOI
10.1364/oe.418323

Related papers

Performance of underwater quantum key distribution with polarization encoding

Shi-Cheng Zhao, Zhao-Qi-Zhi Han, Ya Xiao +3 more

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.

arXiv:1903.01218•Journal of the Optical Society of America A•Apr 23, 2019•35 citations

Practical underwater quantum key distribution based on decoy-state BB84 protocol

Shanchuan Dong, Yonghe Yu, Shangshuai Zheng +4 more

Polarization encoding quantum key distribution has been proven to be a reliable method to build a secure communication system. It has already been used in an inter-city fiber channel and near-Earth atmosphere channel, leaving an underwater channel the last barrier to conquer. Here we demonstrate a decoy-state BB84 quantum key distribution system over a water channel with a compact system design for future experiments in the ocean. In the system, a multiple-intensity modulated laser module is designed to produce the light pulses of quantum states, including signal state, decoy state, and vacuum state. Classical communication and synchronization are realized by wireless optical transmission. Multiple filtering techniques and wavelength division multiplexing are further used to avoid cross talk of different lights. We test the performance of the system and obtain a final key rate of 245.6 bps with an average quantum bit error rate of 1.91% over a 2.4 m water channel, in which the channel attenuation is 16.35 dB. Numerical simulation shows that the system can tolerate up to 21.7 dB total channel loss and can still generate secure keys in 277.9 m Jerlov type I ocean channel.

arXiv:2203.04598•Applied Optics•May 3, 2022•5 citations

Experimental demonstration of underwater decoy-state quantum key distribution with all-optical transmission

Yonghe Yu, Wendong Li, Weidong Yu +8 more

We demonstrate the underwater quantum key distribution (UWQKD) over a 10.4-meter Jerlov type III seawater channel by building a complete UWQKD system with all-optical transmission of quantum signals, a synchronization signal and a classical communication signal. The wavelength division multiplexing and the space-time-wavelength filtering technology are applied to ensure that the optical signals do not interfere with each other. The system is controlled by FPGA and can be easily integrated into watertight cabins to perform the field experiment. By using the decoy-state BB84 protocol with polarization encoding, we obtain a bit rate of secure keys of 1.82 Kbps and an error rate of 1.55% at the attenuation of 13.26 dB. We prove that the system can tolerate the channel loss up to 23.7 dB and therefore may be used in the 300-meter-long Jerlov type I clean seawater channel.

arXiv:2106.13441•Optics Express•Aug 30, 2021•9 citations

Optimized decoy state QKD for underwater free space communication

Minal Lopes, Nisha Sarwade

Quantum cryptography (QC) is envisioned as a solution for global key distribution through fiber optic, free space and underwater optical communication due to its unconditional security. In view of this, this paper investigates underwater free space quantum key distribution (QKD) model for enhanced transmission distance, secret key rates and security. It is reported that secure underwater free space QKD is feasible in the clearest ocean water with the sifted key rates up to 207[Formula: see text]kbps. This paper extends this work by testing performance of optimized decoy state QKD protocol with underwater free space communication model. The attenuation of photons, quantum bit error rate and the sifted key generation rate of underwater quantum communication is obtained with vector radiative transfer theory and Monte Carlo method. It is observed from the simulations that optimized decoy state QKD evidently enhances the underwater secret key transmission distance as well as secret key rates.

International Journal of Quantum Information•Mar 1, 2018•16 citations

Experimental investigation of quantum key distribution over a water channel

Shicheng Zhao, Wendong Li, Yuan Shen +9 more

Quantum key distribution (QKD) has undergone significant development in recent decades, particularly with respect to free-space (air) and optical fiber channels. Here, we report a proof-of-principle experiment for the BB84 protocol QKD over a water channel. First, we demonstrate again the polarization preservation properties of the water channel in optical transmission according to the measured Mueller matrix, which is close to the unit matrix. The reason for the polarization preservation, revealed by Monte Carlo simulation, is that almost all the received photons are unscattered. Then, we performed the first polarization encoding BB84 protocol QKD over a 2.37 m water channel. The results show that QKD can be performed with a low quantum bit error rate, less than 3.5%, with different attenuation coefficients.

arXiv:1903.01171•Applied Optics•May 8, 2019•65 citations

Experimental study on underwater continuous-variable quantum key distribution with discrete modulation

Xinke Tang, Zhen Chen, Zongyao Zhao +2 more

We experimentally demonstrated the feasibility of an underwater continuous-variable quantum key distribution (CV-QKD) system based on four-state protocol, which is promising to guarantee the unconditionally secure underwater wireless optical communication. CV-QKD parameter estimation is performed after transmitting quantum coherent signal from Alice to Bob through a water tank. The secure key rate under collective attack of the demonstrated CV-QKD system is estimated as 22.9 kbits/s at a channel loss of 12.4 dB. In addition, the performance is also investigated with various water types and the maximum underwater transmission distance of the demonstrated CV-QKD system is estimated as 148.7 m in the pure sea water.

Optics Express•Aug 4, 2022•6 citations
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.
Polarization encoding quantum key distribution has been proven to be a reliable method to build a secure communication system. It has already been used in an inter-city fiber channel and near-Earth atmosphere channel, leaving an underwater channel the last barrier to conquer. Here we demonstrate a decoy-state BB84 quantum key distribution system over a water channel with a compact system design for future experiments in the ocean. In the system, a multiple-intensity modulated laser module is designed to produce the light pulses of quantum states, including signal state, decoy state, and vacuum state. Classical communication and synchronization are realized by wireless optical transmission. Multiple filtering techniques and wavelength division multiplexing are further used to avoid cross talk of different lights. We test the performance of the system and obtain a final key rate of 245.6 bps with an average quantum bit error rate of 1.91% over a 2.4 m water channel, in which the channel attenuation is 16.35 dB. Numerical simulation shows that the system can tolerate up to 21.7 dB total channel loss and can still generate secure keys in 277.9 m Jerlov type I ocean channel.
We demonstrate the underwater quantum key distribution (UWQKD) over a 10.4-meter Jerlov type III seawater channel by building a complete UWQKD system with all-optical transmission of quantum signals, a synchronization signal and a classical communication signal. The wavelength division multiplexing and the space-time-wavelength filtering technology are applied to ensure that the optical signals do not interfere with each other. The system is controlled by FPGA and can be easily integrated into watertight cabins to perform the field experiment. By using the decoy-state BB84 protocol with polarization encoding, we obtain a bit rate of secure keys of 1.82 Kbps and an error rate of 1.55% at the attenuation of 13.26 dB. We prove that the system can tolerate the channel loss up to 23.7 dB and therefore may be used in the 300-meter-long Jerlov type I clean seawater channel.
Quantum cryptography (QC) is envisioned as a solution for global key distribution through fiber optic, free space and underwater optical communication due to its unconditional security. In view of this, this paper investigates underwater free space quantum key distribution (QKD) model for enhanced transmission distance, secret key rates and security. It is reported that secure underwater free space QKD is feasible in the clearest ocean water with the sifted key rates up to 207[Formula: see text]kbps. This paper extends this work by testing performance of optimized decoy state QKD protocol with underwater free space communication model. The attenuation of photons, quantum bit error rate and the sifted key generation rate of underwater quantum communication is obtained with vector radiative transfer theory and Monte Carlo method. It is observed from the simulations that optimized decoy state QKD evidently enhances the underwater secret key transmission distance as well as secret key rates.
Quantum key distribution (QKD) has undergone significant development in recent decades, particularly with respect to free-space (air) and optical fiber channels. Here, we report a proof-of-principle experiment for the BB84 protocol QKD over a water channel. First, we demonstrate again the polarization preservation properties of the water channel in optical transmission according to the measured Mueller matrix, which is close to the unit matrix. The reason for the polarization preservation, revealed by Monte Carlo simulation, is that almost all the received photons are unscattered. Then, we performed the first polarization encoding BB84 protocol QKD over a 2.37 m water channel. The results show that QKD can be performed with a low quantum bit error rate, less than 3.5%, with different attenuation coefficients.
We experimentally demonstrated the feasibility of an underwater continuous-variable quantum key distribution (CV-QKD) system based on four-state protocol, which is promising to guarantee the unconditionally secure underwater wireless optical communication. CV-QKD parameter estimation is performed after transmitting quantum coherent signal from Alice to Bob through a water tank. The secure key rate under collective attack of the demonstrated CV-QKD system is estimated as 22.9 kbits/s at a channel loss of 12.4 dB. In addition, the performance is also investigated with various water types and the maximum underwater transmission distance of the demonstrated CV-QKD system is estimated as 148.7 m in the pure sea water.