Last time, I showed you that a simple quantum system, consisting of a single particle in a superposition of traveling from the left OR from the right, leads to a striking quantum interference effect. It can then produce the same kind of result as the famous double-slit experiment.
The pre-quantum version of this system, in which (like a 19th century scientist) I draw the particle as though it actually has a definite position and motion in each half of the superposition, looks like Fig. 1. The interference occurs when the particle in both halves of the superposition reaches the point at center, x=0.
Then I posed a puzzle. I put a system of two [distinguishable] particles into a superposition which, in pre-quantum language, looks like Fig. 2.
with all particles traveling at the same speed and passing each other without incident if they meet. And I pointed out three events that would happen in quick succession, shown in Figs. 2a-2c.
And I asked the Big Question: in the quantum version of Fig. 2, when will we see quantum interference?
- Will we see interference during events 1, 2a, 2b, and 3?
- Will we see interference during events 1 and 3 only?
- Will we see interference during events 2a and 2b only?
- Will we see interference from the beginning of event 1 to the end of event 3?
- Will we see interference during event 1 only?
- Will we see no interference?
- Will we see interference at some time other than events 1, 2a, 2b or 3?
- Something else altogether?
So? Well? What’s the correct answer?
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