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Physics Letters A

Superadditivity in capacity of quantum channel for q-ary linearly dependent real symmetric-state signals

Tsuyoshi Sasaki Usuda, Shogo Usami, Ichi Takumi, Masayasu Hata

Published Dec 1, 2002• 14 citations
Publisher
DOI
10.1016/s0375-9601(02)01413-5

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The amount of information transmissible through a communications channel is determined by the noise characteristics of the channel and by the quantities of available transmission resources. In classical information theory, the amount of transmissible information can be increased twice at most when the transmission resource is doubled for fixed noise characteristics. In quantum information theory, however, the amount of information transmitted can increase even more than twice. We present a proof-of-principle demonstration of this superadditivity of classical capacity of a quantum channel by using the ternary symmetric states of a single photon, and by event selection from a weak coherent light source. We also show how the superadditive coding gain, even in a small code length, can boost the communication performance of the conventional coding technique.