Actually, the system exists in state |1> and |2>, not a1 and a2. But never mind. What is puzzling is that, how did you jump from what you view as what quantum superposition say, to this:That the system can be said to exist in both a1 and a2 states simultaneously. Interference is the result of superpositions of two or more waves(say passing through the double slit experiment). When performing a certain measurement on a quantum state, the result is described by a probability distribution, however we don't observe superpositions, objects in superpositions are not real(do not exist) until the state vector reduction that describes the evolution of the system.
?GeorgCantor said:The problem with decoherence is that it doesn't say that matter(objects) are there all the time with properties in space. On the contrary, though it doesn't explain why we observe exatly what we do, it says that physical structures are not always there. If this doesn't blow one's mind, one must have rocks in his head.
Remember, this was my original question/objection!
I have no idea why you decide to give me a lesson in tunneling. Have YOU done any experiment in quantum tunneling? I have.