> But can we agree that there are states that can be factored, and states that can't, and that this is a useful distinction to make? And that this distinction is physical, i.e. that it produces observable effects? (And not just observable, but interesting and useful?)
If you say so. "All components of a quantum system are always entangled" sounds like a contrary claim to me, but I don't want to quibble over it.
It does make an interesting puzzle, though, how it can be physically possible to prepare a state that is both unentangled and pure. I don't actually know the answer to that off the top of my head.
Oh certainly. I've never disagreed on this haha.