Dear S.P.K.,
try this one, there is a collection of
possible and impossible machines, classical
versus quantic.
s.

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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.