Single-emitter quantum key distribution over 175 km of fibre with optimised finite key rates

• Published in: Nature communications Vol. 14; no. 1; p. 3573
• Main Authors: Morrison, Christopher L., Pousa, Roberto G., Graffitti, Francesco, Koong, Zhe Xian, Barrow, Peter, Stoltz, Nick G., Bouwmeester, Dirk, Jeffers, John, Oi, Daniel K. L., Gerardot, Brian D., Fedrizzi, Alessandro
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 16-06-2023; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/483/3925; 639/766/483/481; Asymptotic properties; Emitters; Humanities and Social Sciences; multidisciplinary; Photons; Quantum cryptography; Quantum dots; Science; Science (multidisciplinary); Telecommunications
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-39219-5

Quantum key distribution with solid-state single-photon emitters is gaining traction due to their rapidly improving performance and compatibility with future quantum networks. Here we emulate a quantum key distribution scheme with quantum-dot-generated single photons frequency-converted to 1550 nm, achieving count rates of 1.6 MHz with
g
2
0
=
3.6
%
and asymptotic positive key rates over 175 km of telecom fibre. We show that the commonly used finite-key analysis for non-decoy state QKD drastically overestimates secure key acquisition times due to overly loose bounds on statistical fluctuations. Using the tighter multiplicative Chernoff bound to constrain the estimated finite key parameters, we reduce the required number of received signals by a factor 10
8
. The resulting finite key rate approaches the asymptotic limit at all achievable distances in acquisition times of one hour, and at 100 km we generate finite keys at 13 kbps for one minute of acquisition. This result is an important step towards long-distance single-emitter quantum networking.
Future single-photon-based quantum networks will require both reliable telecom single-photon sources and improvements in security analysis. Here, the authors show how to use quantum dots and difference frequency generation to perform long-distance QKD, also reducing secure key acquisition time thanks to improved analytical bounds.