  The superposition principle is at the heart of quantum mechanics and at the
root of many paradoxes arising when trying to extend its predictions to our
everyday world. Schroedinger's cat is the prototype of such paradoxes and here,
in contrast to many others, we choose to investigate it from the operational
point of view. We experimentally demonstrate a universal strategy for producing
an unambiguously distinguishable type of superposition, that of an arbitrary
pure state and its orthogonal. It relies on only a limited amount of
information about the input state to first generate its orthogonal one. Then, a
simple change in the experimental parameters is used to produce arbitrary
superpositions of the mutually orthogonal states. Constituting a sort of
Schroedinger's black box, able to turn a whole zoo of input states into
coherent superpositions, our scheme can produce arbitrary continuous-variable
optical qubits, which may prove practical for implementing quantum technologies
and measurement tasks.
