  Modelling quantum devices is to find a model according to quantum theory that
can explain the result of experiments in a quantum device. We find that usually
we cannot correctly identify the model describing the actual physics of the
device regardless of the experimental effort given a limited set of operations.
According to sufficient conditions that we find, correctly reconstructing the
model requires either a particular set of pure states and projective
measurements or a set of evolution operators that can generate all unitary
operators.
