  It is known that no quantum process can produce a predetermined superposition
of unknown arbitrary states. It has already been shown that with some partial
information about the states, one can produce with some probability such
superpositions. Here we show that there are universal machines which can
produce superpositions of unknown orthogonal states with unit probability. Our
construction unravels the relation between the no-cloning theorem and the
no-superposition theorem, that is we show that if a perfect cloning machine
exists, then a universal superposition machine can also exist.
