This may be an easy answer for anybody. Is it possible to detect if a particle A is still in a superposition via the sending a group of particles B through a box containing particle A?
There is Quantum Tomography, but it requires several copies of the same quantum system (that is an apparatus that can prepare the system in the same state several times).
I understand the problem as: You give me a state, I tell you what are coefficients of expansion into eigenbasis. I quess this is not possible. If it were not for the No Cloning theorem, then you could copy the state and do qUantum tomography on the copies.
Again Quantum Nondemolition Measurement does not mean the state is unchanged and in fact this i just an almost perfect projection. There is no hope here either.