# Interference between different kinds of particles

1. Jun 28, 2011

### id the sloth

I have only an completed one course on quantum mechanics so please excuse me if this seems rudimentary.

In my course we only dealt with electrons and their interference with one another. Is it possible for an electron and a proton to interfere with one another? Or more generally, can different types of particles interfere with each other?

2. Jun 28, 2011

Staff Emeritus
No. Only identical particles can interfere - you have to be able to add amplitudes.

3. Jun 28, 2011

### id the sloth

Okay. But the wave functions can still influence each other right? If I were to shoot a proton and neutron at each other and measured the momentum on the proton, assuming I knew the initial momentums, I would be able to figure out the momentum of the neutron in theory. Which means that the wave functions are in an entangled state correct?

4. Jun 29, 2011

### Lapidus

Yes, that's of course correct. If there is an interaction between particles then that will obviously infuence the time evolution of their wave functions.

5. Jun 29, 2011

### id the sloth

Sweet, just making sure. Thanks!

6. Jun 29, 2011

### haael

We can kinda have interference pattern of different particles, at least in theory.

First we get a particle that decays into few others. Say, a neutron decaying into proton, electron and a neutrino. We shoot this neutron and wait. We can say that it is composed of 3 waves of different speeds. When they all are in phase, we have high probability of detecting a neutron. When the time passes and the 3 waves phase out, we have high probability of detecting proton, electron and neutrino. If we wait a bit longer, the waves will eventually reach the same phase again and create a neutron. I'm assuming that all particles move only in one dimension, but it's only a theory.

If we place detectors along the path of this particle, we will get high probability of detecting a neutron at some places and high probability of proton, electron and neutrino at other places.

Even more, if we did a double-slit experiment with a neutron, we would get a sophisticated interference pattern of detecting neutrons, protons, electrons, neutrinos or no particle at all, with some probabilities. This would have to be huge experiment to let the neutron decay in the process. I make an assumption that 3 particles after neutron decay do not move relative to each other, which is not true in nature, but I hope you get the idea.

In general, any two entangled particles of any kind would give something like an interference pattern in the double-slit experiment.

7. Jun 29, 2011

### id the sloth

That is really is interesting. Is that how you model radioactive particles? As the sum of the wave functions of the decay products?

8. Jun 29, 2011

### unusualname

Particles only interfere with themselves, not with other particles.

ie a single photon, electron, elephant can only interfere with itself, not with another photon, electron, elephant.

So obviously a particle could not interfere with a "different kind of particle"

9. Jun 29, 2011

### haael

Unless they are entangled.

Not quite. Rather, you can say that "physical" neutron is a sum of two waves: "ideal" neutron and (proton, electron, neutrino) triple. These 2 waves happen to be the mass states. Real physical neutron is not the mass state. If the decay products didn't interact except turning into a neutron again, and didn't scatter immediately after decay, then you would get something similar to neutrino oscillations.

10. Jun 29, 2011

### id the sloth

In my chem class, the taught us that bonds could be explained as the shared electrons constructively interfering with each other to minimize energy though

11. Jun 29, 2011

### id the sloth

What happens to the "ideal" neutron wave when the "physical" neutron decays?

12. Jun 29, 2011

Staff Emeritus
I don't understand that setup. Once the neutron decays, you have a proton and electron and neutrino propagating more or less freely. Before it decays you have none of these, and justa neutron propagating freely. Nothing is interfering with anything else.

13. Jun 29, 2011

### Drakkith

Staff Emeritus
There is no more neutron wave. Once the Neutron decays it is gone.

14. Jun 29, 2011

### Drakkith

Staff Emeritus
Entangled particles still don't interfere with each other.

I've never heard of this before and it sounds pretty iffy to me. Got a reference?

This doesn't really make sense to me. If you let the neutron decay you would get detections and interference of protons, electrons, and nuetrinos but no neutrons, as they have decayed. (Or rather most of them depending on the amount of time between emission and detection)