2015/04/24 by Masahiro Takeoka, Saikat Guha, Mark M. Wilde · 3 citations
Physics and Astronomy · #quant-ph
paper · pdf · doi:10.1038/ncomms6235
published as Nature Communications, vol. 5, no. 8, page 5235, October 2014 · 9+4 pages, 3 figures. arXiv admin note: text overlap with arXiv:1310.0129
arxiv created 2015/04/24 · arxiv updated 2016/03/29
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. 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.