  Classical cybernetics is a successful meta-theory to model the regulation of
complex systems from an abstract information-theoretic viewpoint, regardless of
the properties of the system under scrutiny. Fundamental limits to the
controllability of an open system can be formalized in terms of the law of
requisite variety, which is derived from the second law of thermodynamics.
These concepts are briefly reviewed, and the chances, challenges and potential
gains arising from the generalisation of such a framework to the quantum domain
are discussed.
