  Quantum theory can be derived from purely informational principles. Five
elementary axioms-causality, perfect distinguishability, ideal compression,
local distinguishability, and pure conditioning-define a broad class of
theories of information-processing that can be regarded as a standard. One
postulate-purification-singles out quantum theory within this class. The main
structures of quantum theory, such as the representation of mixed states as
convex combinations of perfectly distinguishable pure states, are derived
directly from the principles without using the Hilbert space framework.
