Experimental demonstration of scalable quantum key distribution over a thousand kilometers

TL;DR

This paper demonstrates a quantum key distribution protocol capable of secure communication over a record distance of 1079 kilometers, addressing long-distance challenges in quantum cryptography with a novel protocol and experimental validation.

Contribution

The paper introduces the Terra Quantum QKD protocol (TQ-QKD) and provides the first experimental demonstration of secure quantum key distribution over 1079 kilometers.

Findings

Successful QKD over 1079 km distance

Use of erbium amplifiers for signal retransmission

Enhanced security through loss control and quantum indistinguishability

Abstract

Secure communication over long distances is one of the major problems of modern informatics. Classical transmissions are recognized to be vulnerable to quantum computer attacks. Remarkably, the same quantum mechanics that engenders quantum computers offers guaranteed protection against such attacks via quantum key distribution (QKD). Yet, long-distance transmission is problematic since the essential signal decay in optical channels occurs at a distance of about a hundred kilometers. We propose to resolve this problem by a QKD protocol, further referred to as the Terra Quantum QKD protocol (TQ-QKD protocol). In our protocol, we use semiclassical pulses containing enough photons for random bit encoding and exploiting erbium amplifiers to retranslate photon pulses and, at the same time, ensuring that at the chosen pulse intensity only a few photons could go outside the channel even at distances of about a hundred meters. As a result, an eavesdropper will not be able to efficiently utilize the lost part of the signal. The central component of the TQ-QKD protocol is the end-to-end loss control of the fiber-optic communication line since optical losses can in principle be used by the eavesdropper to obtain the transmitted information. However, our control precision is such that if the degree of the leak is below the detectable level, then the leaking states are quantum since they contain only a few photons. Therefore, available to the eavesdropper parts of the bit encoding states representing `0' and `1' are nearly indistinguishable. Our work presents the experimental demonstration of the TQ-QKD protocol allowing quantum key distribution over 1079 kilometers. Further refining the quality of the scheme's components will expand the attainable transmission distances. This paves the way for creating a secure global QKD network in the upcoming years.