Experimental Demonstration of Underwater Decoy-state Quantum Key Distribution with All-optical Transmission

TL;DR

This paper reports the successful underwater quantum key distribution over a 10.4-meter seawater channel using an all-optical system with decoy-state BB84 protocol, achieving high secure key rates and demonstrating potential for longer distances.

Contribution

It presents the first complete all-optical UWQKD system with multiplexing and filtering, demonstrating secure key distribution in seawater and analyzing its loss tolerance.

Findings

Secure key rate of 1.82 Kbps at 13.26 dB attenuation

System tolerates up to 23.7 dB channel loss

Potential for 300-meter seawater quantum communication

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, synchronization signal and 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 field experiment. By using the decoy-state BB84 protocol with polarization encoding, we obtain a secure key rate of 1.82Kbps and an error rate of 1.55% at the attenuation of 13.26dB. We prove that the system can tolerate the channel loss up to 23.7dB, therefore may be used in the 300-meter-long Jerlov type I clean seawater channel.