The problem is the insistence that there are two distinct particles that have an independent existence and properties. There isn't. There's just a quantum field which when it interacts with other fields in a measuring apparatus produces classical results in accordance with qm. Trying to understand what's really going on in terms of distinct and separate particles is never going to work.
The emphasis of the question should be on “exactly one”. How does using fields instead of particles resolve the question of the collapse of the wave function?
