Instruments and mutual entropies in quantum information
arXiv:quant-ph/0412116
Abstract
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"