Double-Slit Experiment vs Identical Particles

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Discussion Overview

The discussion centers around the conditions necessary for a double-slit experiment to exhibit an interference pattern, particularly focusing on the properties of the source of photons or other quantum particles. Participants explore whether identical quantum states are required or if having the same energy suffices for the experiment to work.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether monochromatic photons are sufficient for interference or if they must be in the same quantum state.
  • Another participant suggests that while the wavefunction of each photon can interfere with itself, having the same wavelength is necessary to resolve a clear interference pattern, otherwise multiple patterns may overlap.
  • A later reply emphasizes that if the properties of photons are altered after passing through the slits, such as changing their polarization, the interference pattern may disappear due to the potential to distinguish the paths taken by the photons.
  • One participant expresses confusion regarding the concept of indistinguishable particles and how it relates to the discussion of single particles and their wavefunctions.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of identical properties for the particles involved in the double-slit experiment. There is no consensus on whether identical quantum states are required or if similar energy levels suffice.

Contextual Notes

Participants have not fully defined terms such as "indistinguishable particles" or "identical particles," leading to some ambiguity in the discussion. The implications of altering particle properties post-slit are also not fully explored.

LarryS
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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?
 
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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.
 
the_house said:
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”.
 
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?
 

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