Experimental quantum key distribution beyond the repeaterless secret key capacity

TL;DR

This paper experimentally demonstrates a quantum key distribution scheme that surpasses the fundamental repeaterless secret key capacity over high-loss channels, marking a significant advancement in quantum communication technology.

Contribution

First experimental demonstration of a quantum key distribution scheme exceeding the repeaterless secret key capacity over channels with losses over 90 dB.

Findings

Secure key rate exceeds the repeaterless secret key capacity.

Successful operation over channels with losses greater than 90 dB.

Demonstrates feasibility of advanced quantum communication protocols.

Abstract

Quantum communications promise to revolutionise the way information is exchanged and protected. Unlike their classical counterpart, they are based on dim optical pulses that cannot be amplified by conventional optical repeaters. Consequently they are heavily impaired by propagation channel losses, which confine their transmission rate and range below a theoretical limit known as repeaterless secret key capacity. Overcoming this limit with today's technology was believed to be impossible until the recent proposal of a scheme that uses phase-coherent optical signals and an auxiliary measuring station to distribute quantum information. Here we experimentally demonstrate such a scheme for the first time and over significant channel losses, in excess of 90 dB. In the high loss regime, the resulting secure key rate exceeds the repeaterless secret key capacity, a result never achieved before. This represents a major step in promoting quantum communications as a dependable resource in today's world.