600-km repeater-like quantum communications with dual-band stabilization

• Published in: Nature photonics Vol. 15; no. 7; pp. 530 - 535
• Main Authors: Pittaluga, Mirko, Minder, Mariella, Lucamarini, Marco, Sanzaro, Mirko, Woodward, Robert I., Li, Ming-Jun, Yuan, Zhiliang, Shields, Andrew J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2021; Nature Publishing Group
• Subjects: 639/624/400/482; 639/766/483/481; Applied and Technical Physics; Channel stabilization; Communication; Experiments; Lasers; Light; Noise; Optical fibers; Photonics; Physics; Physics and Astronomy; Protocol; Quantum cryptography; Quantum Physics; Rayleigh scattering; Sensors; Wavelengths
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-021-00811-0

Twin-field (TF) quantum key distribution (QKD) fundamentally alters the rate-distance relationship of QKD, offering the scaling of a single-node quantum repeater. Although recent experiments have demonstrated the new opportunities for secure long-distance communications allowed by TF-QKD, formidable challenges remain to unlock its true potential. Previous demonstrations have required intense stabilization signals at the same wavelength as the quantum signals, thereby unavoidably generating Rayleigh scattering noise that limits the distance and bit rate. Here, we introduce a dual-band stabilization scheme that overcomes past limitations and can be adapted to other phase-sensitive single-photon applications. Using two different optical wavelengths multiplexed together for channel stabilization and protocol encoding, we develop a setup that provides repeater-like key rates over communication distances of 555 km and 605 km in the finite-size and asymptotic regimes respectively and increases the secure key rate at long distance by two orders of magnitude to values of practical relevance. Twin-field quantum key distribution over 600 km is demonstrated. The key ingredient for success is the dual-band phase stabilization that dramatically reduce the phase fluctuations on optical fibre by more than four orders of magnitude.