What don't you understand? That they are talking about a single particle? A 'single particle in two places' just means the wave-function is distributed into mu

What don't you understand? That they are talking about a single particle? A 'single particle in two places' just means the wave-function is distributed into multiple chunks. Entanglement means that two particles' states are not independent. So it seems like that sentence is talking about how two chunks of a particle's wave-function are not independent, which is probably very obvious. The obviousness of that means it's not sexy confusing quantum magic, so you don't hear much about it as much. This guy is suggesting that you might be able measure mass differences dependent on the form of the wave-function, which would be very interesting. That's how I understand it anyway. I could be full of crap.