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Reading about Young's double slit experiment for electrons, it is stated that the diffraction pattern is observed when both slits are open but not for a single slit (I suppose this is equivalent to there being no diffraction pattern when an observer is placed to measure which slit the electron passes through).

And yet a diffraction pattern is observed for light passing through a single slit. I have not read about this being observed for electrons. Why is this so? I would think that the wave functions describing all matter particles are of the same form and would behave in the same way. I did think that perhaps it had to do with not being able to create small enough slits to observe the electron diffraction pattern, but that cannot be true because the spacing of fringes for two slits and one wide slit is the same if the distance between slits is the same as the width of the single slit. So if we can create small enough slits to space them d apart, then surely we can create a single slit of width d?

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    $\begingroup$ Please give references to the claims. Diffraction always occurs, it's just that the pattern is very different when wave passes through two slits vs one slit. $\endgroup$ – Ruslan Feb 19 '17 at 11:58
  • $\begingroup$ Where did you hear that?I don't think what you said is true. $\endgroup$ – Lapmid Feb 19 '17 at 12:14
  • $\begingroup$ I am reading Quantum Mechanics, 2nd edition, Bransden and Joachain. It states 'it should be noted that if one slit is closed in a two slit experiment, the diffraction pattern does not appear' Oh I see. I think this does apply to this case because the slits are so narrow that a sibgle slit diffraction pattern would be so spread out you would only perhaps see one minimum at the very peripheries of the screen- hardly noticeable. The slot width would have to be increased to about the slit separation to see a noticeable pattern from a single slit. $\endgroup$ – Meep Feb 19 '17 at 12:44
  • $\begingroup$ It can be useful to distinguish the words "diffraction" and "interference". With two slits you get diffraction from each slit and also interference of the waves from the two slits. With one slit you get just the diffraction pattern associated with that slit. Note however that with electrons there are also electrostatic forces which have to be taken into account in the analysis of any precise experiment. $\endgroup$ – Andrew Steane Nov 13 at 11:33
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You are right.

If you are able to create a single slit whose width is of the order of the de Broglie wave-length of a beam of electrons, then you should observe an intereference pattern.

And this has actually been done experimentally, see for instance: https://doi.org/10.1119/1.1987592.

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After a long search with variations, I got a PDF of the recent paper on single slit interference of electrons. From the abstract:

We have performed this experiment with one slit, instead of two, where ballistic electrons within two-dimensional electron gas diffract through a small orifice formed by a quantum point contact (QPC). As the QPC width is comparable to the electron wavelength, the observed intensity profile is further modulated by the transverse waveguide modes present at the injector QPC.

the paper itself is here

enter image description here

enter image description here

The complexity is due to the fact they are also checking for the Aharonof Bohm phases, and the paper needs careful reading, but the figures do show diffraction from single slit.

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