Accessible information and optimal strategies for real symmetrical quantum sources

Masahide Sasaki, Stephen M. Barnett, Richard Jozsa, Masao Osaki, Osamu Hirota

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We study the problem of optimizing the Shannon mutual information for sources of real quantum states, i.e., sources for which there is a basis in which all of the states have only real components. We consider in detail the sources EM of M equiprobable quantum bit (qubit) states lying symmetrically around the great circle of real states on the Bloch sphere and give a variety of explicit optimal strategies. We also consider general real group-covariant sources for which the group acts irreducibly on the subset of all real states and prove the existence of a real group-covariant optimal strategy, extending a theorem of Davies [E. B. Davies, IEEE. Inf. Theory IT-24, 596 (1978)]. Finally, we propose an optical scheme to implement our optimal strategies, simple enough to be realized with present technology.
Original languageEnglish
Article number3325
Number of pages16
JournalPhysical Review A
Issue number5
Publication statusPublished - May 1999


  • quantum states
  • qubit
  • optimal strategies
  • optics
  • optical physics

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