Instruments and mutual entropies in quantum information
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General quantum measurements are represented by instruments. In this paper the mathematical formalization is given of the idea that an instrument is a channel which accepts a quantum state as input and produces a probability and an a posteriori state as output. Then, by using mutual entropies on von Neumann algebras and the identification of instruments and channels, many old and new informational inequalities are obtained in a unified manner. Such inequalities involve various quantities which characterize the performances of the instrument under study; in particular, these inequalities include and generalize the famous Holevo's bound.
LaTeX, requires macros in mypreprint.sty, 16 pages. Submitted to Proceedings of the 25th Conference on "Quantum Probability and Related topics"
LaTeX, requires macros in mypreprint.sty, 16 pages. Submitted to Proceedings of the 25th Conference on "Quantum Probability and Related topics"