Why don't the Slits collapse the wave function?

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SUMMARY

The discussion centers on the phenomenon of wave function collapse in quantum mechanics, particularly in the context of the double-slit experiment. Participants explore the distinction between interactions with slits and measurement devices, emphasizing that the slits do not collapse the wave function due to their lack of internal degrees of freedom. The conversation references key concepts such as superposition, phase coherence, and the role of measurement in determining quantum states. Notable sources mentioned include Penrose's works and Datta's "Electron Transport in Mesoscopic Systems."

PREREQUISITES
  • Understanding of quantum mechanics principles, including wave function and superposition.
  • Familiarity with the double-slit experiment and its implications for quantum behavior.
  • Knowledge of phase coherence and its significance in interference patterns.
  • Basic concepts of measurement theory in quantum mechanics.
NEXT STEPS
  • Study the implications of the Copenhagen interpretation of quantum mechanics.
  • Explore the concept of phase coherence in quantum systems.
  • Investigate the role of measurement devices in quantum mechanics, particularly in relation to wave function collapse.
  • Read Datta's "Electron Transport in Mesoscopic Systems" for insights on quantum transport phenomena.
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Quantum physics enthusiasts, students of theoretical physics, and researchers interested in the foundational aspects of quantum mechanics and wave function behavior.

  • #91
DrChinese said:
There is a way to learn which slit the photon pass through without absorbing it. If you put a polarizer in front (or behind) each slit, and the polarizers are crossed (at 90 degrees apart as to their relative orientation), then the photon passes through. Because of the polarizer, you know which slit it passed through (or could learn later); therefore there is no interference pattern.

I can see two situations here. If we send toward the slits a circular polarized photon, then each component of linear polarization would pass through each slit and then re-combine. The interference pattern would still be there.
If we sent a linearly polarized photon with either horizontal or vertical polarization, then we would know which slit it went through. Every photon that lands on the screen would be coming from the slit that corresponds to its initial polarization. In this case I guess the interference pattern would be destroyed. But I also think that 50% of the time the photon would be absorbed by the polarizer film in the slit with crossed polarization. If you use a polarizer that works by reflection, in that case you could absorb the photon after being reflected. So I don't know if this would qualify as a non-absorption detection experiment. It would also be equivalent to putting any obstacle in front of one of the slits. What you are detecting is the photon that doesn't make it through and not the one that does.
Well Dr. Chinese you got me thinking for a while. This is an interesting modification of the double-slit experiment and I had fun thinking about it.
 

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