Abstract
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.
Highlights
Quantum key distribution (QKD), a way of generating and distributing secret keys based on quantum physics, is considered unconditionally secure
The addition of the acquisition pointing tracking (APT) system requires the introduction of additional classical optical signals, and our experiments have proved the feasibility of adding classical signals in the quantum key distribution system
We develop an underwater decoy-state quantum key distribution system, and perform the quantum key distribution experiment through 10.4m Jerlov type III seawater channel
Summary
Quantum key distribution (QKD), a way of generating and distributing secret keys based on quantum physics, is considered unconditionally secure. Underwater optical communication is even more difficult due to the complexity of the underwater channel and the interactions among the quantum, classical and synchronization signals. Another challenge brought by the underwater channel is that the underwater instrument should be designed in small size and with high integration, and should be controlled with elaborately designed field-programmable gate array (FPGA) system. We successfully implement a complete decoy-state BB84 UWQKD system with polarization encoding and all-optical transmission, in which the optical setup, FPGA boards, and software work together. The software in the PCs completes error-correction, error checking, and privacy amplification With this UWQKD system, real-time secret keys can be generated
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