Double-Slit Experiment vs Identical Particles

[LarryS]

Will a double-slit experiment work (exhibit an interference pattern) with a source of photons that is just monochromatic or do the photons need to be in the same quantum state?

More generally, do all properties of a source of quantum particles need to be identical in order for the double-slit experiment to work, or do they just need to have the same energy?

 

[the_house]

Since the wavefunction of each photon (or whatever particle you're using) can interfere with itself, the properties of the other particles don't really matter much. To actually see the interference pattern, though, everything should have the same wavelength. Otherwise you'd just have a bunch of different interference patterns superposed on top of each other and you wouldn't be able to resolve anything.

 

[LarryS]

Since the wavefunction of each photon (or whatever particle you're using) can interfere with itself, the properties of the other particles don't really matter much. To actually see the interference pattern, though, everything should have the same wavelength. Otherwise you'd just have a bunch of different interference patterns superposed on top of each other and you wouldn't be able to resolve anything.

Yes, that is true, but if you do something to the photons that took one of the paths after they pass through the slits (half-silvered mirror, etc.), like changing their polarization, then the interference pattern disappears because it becomes theoretically possible to determine which route the photon took. They are no longer indistinguishable at the time of measurement. I should have titled my post “Define Indistinguishable Particles” or “Define Identical Particles”.

 

[the_house]

I guess I'm not sure what the confusion is. In all the scenarios you've talked about, there's just a single particle whose wavefunction may or may not consist of an interference pattern.

What's all this about indistinguishable particles?