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A collapsed state should act like a particle and a non-collapsed like a wave. Is this statement true? So if you had a single slit and detectors behind it off to the sides... The collapsed state should form a bar through the slit and the non-collapsed should spread out like a wave. So then the detectors to the side should show higher activity for non-collapsed states than for collapsed states, right? Let's assume background interference and internal noise are not issues. Will this technique work?

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  • $\begingroup$ Could you please also cite a source for the info. $\endgroup$
    – Aryagm
    Oct 28, 2020 at 14:51

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There's no such thing as a collapsed state. Wavefunction collapse alters the state, but afterwards it's still a quantum state evolving according to the Schrödinger equation; it's as wavelike as any other state.

Possibly you were confused by diagrams that show "persistent particle-like behavior" after measurement in the double slit experiment. Here's one from a Stack Exchange question, and here's another from a Stack Exchange answer. These diagrams are incorrect. It would be possible in principle for a detector to focus the particle's path like that, but if it did, then the focusing itself would explain the lack of interference, with no need for wavefunction collapse. In the standard double-slit-with-detectors thought experiment, the light from both slits spreads out after detection and covers largely the same part of the screen, because it's only in that situation that you need wavefunction collapse to explain the lack of an interference pattern. So the answer to your question is no: the detectors at the sides (edges of the screen) will register about the same amount of light whether the detectors at the slits are present or not.

I don't have a source, but any good textbook will show the correct single-slit behavior. If it has diagrams like the ones I linked above then it isn't a good textbook. (Unless the two lines are meant to illustrate the behavior of actual classical particles, in which case it's fine.)

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  • $\begingroup$ Thanks a lot. But is there any other way to detect a collapse in wave function? $\endgroup$
    – Aryagm
    Oct 28, 2020 at 19:32

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