Double slit experiment with electrons

cygnet1

In the double-slit experiment, without which-path information available, the diffraction pattern is usually shown as an even function with respect to the displacement from the midpoint of the slits: something like sin ay / y. (This is the case in Feynman's lectures, and many others.) The question was posed as to whether this result is valid for spin-aligned electrons. The most direct reply stated that it is indeed valid:

Originally Posted by Wallin
Can anyone direct me to any version of the double-slit experiment which used only electrons with aligned spin axes? If you can't direct me to an experiment, can you postulate how or if the double-slit experiment might be different using such electrons?

Thanks!

As has probably been stated (although not explicitly that I can see), using aligned spin electrons has no effect on the final result of interference (i.e. probability to find an electron at a certain position). This is analogous to using polarised light in a double-slit experiment. Sending the electrons through a slit has no effect on the spin of the electron.

This seems to contradict these UC Berkeley course notes, which state that if one of the paths is increased in length to make it out of phase from the other by 2∏ radians, then the interference pattern will go to zero, because the state function of the longer path will be multiplied by -1 (or exp i∏). It is stated in the notes that this effect was experimentally confirmed with neutrons (another fermion). This would not be the case for photons, which would constructively interfere.

If this is indeed correct, then wouldn't it also be true that if the electron source were symmetrically placed between the two slits, that there would be places in the diffraction pattern that would be different with photons?

So who's right? The Berkeley professor or Feynman?

Note: It appears the Berkeley notes refer to a magnetic field, B₀, which may have something to do with it.

Simon Bridge

They are talking about different experiments.
In your quoted section they are talking about the probability of finding an electron at a particular place while in the notes, they are talking about finding a particular spin state at that place.

cygnet1

Actually, I think I've answered my own question. The Berkeley lecture notes show a magnetic field in one path but not the other. It is that field that changes the spin and demonstrates the spin-1/2 nature of the fermions.

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Simon Bridge Recognitions: Homework Help	They are talking about different experiments. In your quoted section they are talking about the probability of finding an electron at a particular place while in the notes, they are talking about finding a particular spin state at that place.

cygnet1	Actually, I think I've answered my own question. The Berkeley lecture notes show a magnetic field in one path but not the other. It is that field that changes the spin and demonstrates the spin-1/2 nature of the fermions.