# Experimental investigation of quantum key distribution over water channel

## TL;DR

This paper presents the first experimental demonstration of quantum key distribution over a water channel, showing polarization preservation and successful BB84 protocol implementation with low error rates.

## Contribution

It is the first to experimentally demonstrate BB84 QKD over water, revealing polarization preservation and low error rates in such channels.

## Key findings

- QKD achieved with QBER less than 3.5%
- Water channel preserves polarization properties
- Successful implementation over 2.37m water channel

## Abstract

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 the first proof-of-principle experiment for the BB84 protocol QKD over a water channel. Firstly, 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 2.37m water channel. The results show that QKD can be performed with a low quantum bit error rate (QBER), less than 3.5%, with different attenuation coefficients.

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Source: https://tomesphere.com/paper/1903.01171