Source-linked AI summary
Long-distance quantum key distribution secure against coherent attacks
Bernd Fröhlich, Marco Lucamarini, James F. Dynes, Lucian C. Comandar, Winci W. -S. Tam, Alan Plews, Andrew W. Sharpe, Zhiliang Yuan, Andrew J. Shields
TL;DR
QKD experiments have struggled to combine finite-size security against coherent attacks with long-distance transmission and practical hardware. This work implements efficient decoy-state BB84 and demonstrates secure key transmission over 240 km without multiplexing and 200 km with conventional-signal multiplexing, using thermo-electrically cooled detectors.
Problem
Finite-size QKD experiments have often lacked rigorous security against coherent attacks, while practical long-distance coexistence with conventional data transmission remains challenging.
Method
The authors implement two efficient decoy-state BB84 variants with security proofs against coherent attacks in a state-of-the-art system using thermo-electrically cooled single-photon detectors.
Results
Secure key transmission reaches 240 km without multiplexing and 200 km with conventional data transmission multiplexed over the quantum channel.
Takeaways & Limitations
Practical thermo-electrically cooled QKD systems can support secure transmission beyond 200 km and coexist with 100G data signals over 150 km.
Takeaways & Limitations
Entanglement-based and measurement-device-independent QKD can provide coherent-attack security but often have impractically low key rates or require more complex apparatus.
Abstract
from arXiv · showhide
Quantum key distribution (QKD) permits information-theoretically secure transmission of digital encryption keys, assuming that the behaviour of the devices employed for the key exchange can be reliably modelled and predicted. Remarkably, no assumptions have to be made on the capabilities of an eavesdropper other than that she is bounded by the laws of Nature, thus making the security of QKD "unconditional". However, unconditional security is hard to achieve in practice. For example, any experimental realisation can only collect finite data samples, leading to vulnerabilities against coherent attacks, the most general class of attacks, and for some protocols the theoretical proof of robustness against these attacks is still missing. For these reasons, in the past many QKD experiments have fallen short of implementing an unconditionally secure protocol and have instead considered limited attacking capabilities by the eavesdropper. Here, we explore the security of QKD against coherent attacks in the most challenging environment: the long-distance transmission of keys. We demonstrate that the BB84 protocol can provide positive key rates for distances up to 240 km without multiplexing of conventional signals, and up to 200 km with multiplexing. Useful key rates can be achieved even for the longest distances, using practical thermo-electrically cooled single-photon detectors.