Coherent phase transfer for real-world twin-field quantum key distribution

Cecilia Clivati*, Alice Meda, Simone Donadello, Salvatore Virzì, Marco Genovese, Filippo Levi, Alberto Mura, Mirko Pittaluga, Zhiliang Yuan, Andrew J. Shields, Marco Lucamarini, Ivo Pietro Degiovanni, Davide Calonico

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Quantum mechanics allows distribution of intrinsically secure encryption keys by optical means. Twin-field quantum key distribution is one of the most promising techniques for its implementation on long-distance fiber networks, but requires stabilizing the optical length of the communication channels between parties. In proof-of-principle experiments based on spooled fibers, this was achieved by interleaving the quantum communication with periodical stabilization frames. In this approach, longer duty cycles for the key streaming come at the cost of a looser control of channel length, and a successful key-transfer using this technique in real world remains a significant challenge. Using interferometry techniques derived from frequency metrology, we develop a solution for the simultaneous key streaming and channel length control, and demonstrate it on a 206 km field-deployed fiber with 65 dB loss. Our technique reduces the quantum-bit-error-rate contributed by channel length variations to <1%, representing an effective solution for real-world quantum communications.

Original languageEnglish
Article number157
Number of pages8
JournalNature Communications
Issue number1
Publication statusPublished - 10 Jan 2022

Bibliographical note

Funding Information:
We thank Consortium Top-IX, especially Matteo Frittelli and Alessandro Galardini, for technical assistance on deployed fibers and helpful discussions on the network design; PPQSense for the fruitful collaboration in customizing the lasers drivers. M.L. and Z.Y. have carried out part of this work at Toshiba Europe Ltd. This project received funding from: the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 951886 (CLONETS-DS); Grant Agreement No. 857156 (OpenQKD); Grant Agreement No. 675662 (QCall); project Nato-G5263; project ARS01_00734-QUANCOM (European structural and investment funds MUR-PON Ricerca & Innovazione 2014-2020).

Publisher Copyright:
© 2022, The Author(s).

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