Theoretically, is macroscopic quantum superposition possible? We know that quantum overlap has currently managed to do so in up to 2000 atoms, more and more limits are breaking.
 A: Theoretically, every object is always in some form of superposition of states. If a particle is in a pure energy state, that is a superposition of position states, and vice versa. More generally any wave function can always be expressed as a superposition of suitable basis functions.
Perhaps what your question was getting at was whether is is possible to generate quantum interference effects between large objects. In theory the answer is yes, in practice it is difficult because to achieve interference you need to maintain a phase relationship of some sort between the interfering functions. In practice it is hard to isolate systems from interactions with their environment, which introduces all sorts of random changes to their wave-functions.
A: In my opinion it is always possible to put an object in a superposition of states by making use of the uncertainty principle. So, if you want to put an object in a superposition of two position states you can do that by measuring its momentum accurately enough. The problem is that it is simply not possible to measure the momentum of, say, 1Kg iron ball so precisely that the uncertainty in its position would be detectable (say, 1m).
Now, there is the claim that you could achieve such macroscopic superpositions by letting the iron ball be moved by a mechanism sensitive to, say, the spin of a particle prepared in a spin-superposition state. By perfectly isolating the entire experiment in some sort of a magical box, the story goes, you may get a superposition as large as 1 m or more.
In my opinion, such magical boxes are physically impossible. There is no way to block the gravitational field for example, so it is always possible to determine the location of the ball inside the box by measuring the position of its center of mass from outside with a torsion balance for example. So I think such macroscopic superpositions, extending beyond the uncertainty limit, cannot exist.
