  Quantum theory was discovered in an adventurous way, under the urge to solve
puzzles-like the spectrum of the blackbody radiation-that haunted the physics
community at the beginning of the 20th century. It soon became clear, though,
that quantum theory was not just a theory of specific physical systems, but
rather a new language of universal applicability. Can this language be
reconstructed from first principles? Can we arrive at it from logical
reasoning, instead of ad hoc guesswork? A positive answer was provided in Refs.
[1, 2], where we put forward six principles that identify quantum theory
uniquely in a broad class of theories. We first defined a class of "theories of
information", constructed as extensions of probability theory in which events
can be connected into networks. In this framework, we formulated the six
principles as rules governing the control and the accessibility of information.
Directly from these rules, we reconstructed a number of quantum information
features, and eventually, the whole Hilbert space framework. In short, our
principles characterize quantum theory as the theory of information that allows
for maximal control of randomness.
