Dear S.P.K., try this one, there is a collection of possible and impossible machines, classical versus quantic. s.
Quantum Information Theory - an Invitation http://arxiv.org/abs/quant-ph/0101061 Authors: R. F. Werner Comments: 51 pages, 12 Figures, LaTeX+dvips. Will appear in a volume "Quantum information - an introduction to basic theoretical concepts and experiments" in Springer Tracts in Modern Physics We give a non-technical introduction of the basic concepts of Quantum Information Theory along the distinction between possible and impossible machines. We then proceed to describe the mathematical framework of Quantum Information Theory. The capacities of a quantum channel for classical and for quantum information are defined in a unified scheme, and a mathematical characterization of all teleportation and dense coding schemes is given.
