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The double slit experiment with either photons or electrons shows that when they are emitted from one slit, they will behave like particles and show one dot on the imaging screen, but if they are emitted from both slits simultaneously in large enough quantities, an in interference pattern will be observed. But what if photons were emitted from one slit and electrons from the other? Would you see two dots or an interference pattern?

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Don't think of photons or electrons as being emitted by the slits. The photons or electrons are emitted by a single coherent source (e.g., an electron linear accelerator or a laser). The pattern that is formed on the screen depends on whether the beam from that single source passes through one slit or two parallel slits.

The idea that the single source is coherent is incompatible with it being a source of two different kinds of thing (e.g., electrons and photons).

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  • $\begingroup$ Wave interference does not require a coherent source (with all photons in phase). The spectrum from a line filament bulb or a linear gas discharge tube can easily be observed with a multi-slit grating. It has been suggested that the wave packet associated with each photon passing through a slit system produces the pattern that determines the probability that the photon will be detected at a particular point. $\endgroup$
    – R.W. Bird
    Feb 20, 2020 at 19:49
  • $\begingroup$ @R.W.Bird To obtain a simple, regular pattern of dark and light bands, you need coherent light. Each different wavelength yields its own distinct pattern with the period of the dark and light bands depending on both the geometry of the experiment and the wavelength. The colorful pattern that Young observed when he first performed the experiment using sunlight (e.g, like this) was the sum of infinitely many distinct interference patterns for the infinitely many distinct wavelengths in sunlight. $\endgroup$ Feb 20, 2020 at 20:03
  • $\begingroup$ For a simple pattern, monochromatic light is nice; coherence is not required. $\endgroup$
    – R.W. Bird
    Feb 20, 2020 at 21:20
  • $\begingroup$ @R.W.Bird, Not sure why you're saying "coherence is not required." If you mean that a coherent source is not needed to replicate Thomas Young's experiment, then sure, that's true, but I don't see how it helps to answer the OP's question. OTOH, if you think that "monochromatic light" is not coherent, then I think you're only half right. To get the best-defined interference pattern, you need monochromatic light with rays that all appear to come from the same, tiny point source. Light that has both of those qualities is coherent. $\endgroup$ Feb 20, 2020 at 22:36
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    $\begingroup$ Perhaps my understanding of the term coherence is to limited. I've been thinking that it referred to the idea that the wave packets associated with the photons in a laser beam were all in phase as a result of stimulated emission. $\endgroup$
    – R.W. Bird
    Feb 21, 2020 at 14:10
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To answer Rob's question: Uniformly illuminating one slit with a beam of electrons and a near-by slit with a beam of photons would be difficult. One would expect each to produce a single slit diffraction pattern (perhaps detected by a strip of film). The question then is: Would the EM wave packets associated with the photons interact with the wave packets associated with the electrons (also EM?) to produce a double slit pattern? That sounds like an experiment worth trying (perhaps with circular apertures).

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  • $\begingroup$ I tried to find in the literature an example of someone doing this and was unsuccessful. Perhaps coherent light will give the clearest pattern, but will a photon and electron beam create any interference pattern? $\endgroup$
    – Rob
    Feb 21, 2020 at 16:10
  • $\begingroup$ In other words, do the two beams need to have similar de Broglie wavelengths to form interference patterns? $\endgroup$
    – Rob
    Feb 21, 2020 at 16:58
  • $\begingroup$ The wavelength of the wave packets associated with a beam of electrons can probably adjusted by changing the accelerating voltage, but I've come to realize that Solomon Slow is correct. For two beams from different sources to produce a stable interference pattern, both must be perfectly coherent. All wave packets from both beams must be of the same wavelength and in phase. I have no idea how one would produce a coherent beam of electrons. $\endgroup$
    – R.W. Bird
    Feb 21, 2020 at 18:41

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