Fundamental rate-loss tradeoff for optical quantum key distribution

Masahiro Takeoka, Saikat Guha, Mark M. Wilde

Research output: Contribution to journalArticlepeer-review

296 Citations (Scopus)


Since 1984, various optical quantum key distribution (QKD) protocols have been proposed and examined. In all of them, the rate of secret key generation decays exponentially with distance. A natural and fundamental question is then whether there are yet-to-be discovered optical QKD protocols (without quantum repeaters) that could circumvent this rate-distance tradeoff. This paper provides a major step towards answering this question. Here we show that the secret key agreement capacity of a lossy and noisy optical channel assisted by unlimited two-way public classical communication is limited by an upper bound that is solely a function of the channel loss, regardless of how much optical power the protocol may use. Our result has major implications for understanding the secret key agreement capacity of optical channels - a long-standing open problem in optical quantum information theory - and strongly suggests a real need for quantum repeaters to perform QKD at high rates over long distances.

Original languageEnglish
Article number5235
JournalNature communications
Publication statusPublished - 2014 Oct 24
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Physics and Astronomy(all)


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