Wave packet experimental detection

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Discussion Overview

The discussion revolves around the concept of wave function collapse in quantum mechanics, particularly in the context of experimental detection of wave packets. Participants explore the implications of measurement on quantum states, the nature of collapse, and the challenges associated with measuring wave-packet dynamics.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants express dissatisfaction with the concept of wave function collapse, questioning its necessity and implications in quantum theory.
  • One participant argues that collapse is dependent on the specific measurement made and highlights the irreversible nature of certain measurements, such as detecting a photon via the photoelectric effect.
  • Another participant notes that the meaning of "collapse" varies with different interpretations of quantum mechanics and emphasizes that without a specific interpretation, collapse is merely a mathematical update following a measurement.
  • A participant describes the Stern-Gerlach experiment as an example of a measurement that results in a state update, illustrating how the measurement process can entangle position and spin states.
  • There is a reiteration that the discussion of interpretations of quantum mechanics should be reserved for a different subforum, indicating a boundary on the current discussion's scope.

Areas of Agreement / Disagreement

Participants generally do not reach a consensus on the nature and necessity of wave function collapse, with multiple competing views expressed regarding its interpretation and implications.

Contextual Notes

Participants acknowledge that the definition and implications of wave function collapse are contingent on the interpretation of quantum mechanics adopted, which remains unresolved in this discussion.

VVS2000
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TL;DR
Are there any experimental setups that verify the wave packet dynamics we work with in quantum mechanics?
It just came up in my QM class while we were discussing and even my teachers could'nt figure it out
I know the wave function "collapses" when a measurement is made but still not satisfied with it
 
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Rightfully so. The "collapse" is a very questionable concept and not really needed for the physical interpretation of quantum theory. It's obvious that it depends on the specific measurement made on the measured object, which state this object takes after a measurement has been made. E.g., if you detect a photon in the usual way using the photoelectric effect (e.g., using a CCD cam or a photoplate) this photon gets absorbed and is thus gone for good.

It's of course very difficult to measure "wave-packet dynamics". An example is this:

https://doi.org/10.1103/PhysRevLett.72.3783
https://pure.uva.nl/ws/files/2978244/478_5187y.pdf
 
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VVS2000 said:
I know the wave function "collapses" when a measurement is made
Exactly what "collapse" means depends on which QM intepretation you adopt. Note that discussion of particular interpretations belongs in the interpretations subforum.

In the absence of any particular interpretation, "collapse" is just the mathematical procedure we use to update our model when we know the result of a measurement, and no assertion is made at all about what, if anything, "actually happens".
 
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The "collapse" is simply the update of the state after the interaction with a "filter". This idealized "von Neumann filter measurements" are very rarely achieved. An example is the Stern-Gerlach experiment for measuring and preparing spin states of an atom (in the original experiment silver atoms). Here the atom is send through an inhomogeneous magnetic field. According to quantum mechanics the atom moves in different discrete directions depending on the value of the spin component in direction of the magnetic field. Then the position (or momentum) of the atom is entangled with this value of the spin component, i.e., you can just block all atoms which are at positions referring to the spin value you don't want, and thus all atoms going through this filter have a determined spin component in direction of the magnetic field, and you describe them by a corresponding wave function which is a eigenstate of this spin component with the eigenvalue you filtered out.
 
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PeterDonis said:
Exactly what "collapse" means depends on which QM intepretation you adopt. Note that discussion of particular interpretations belongs in the interpretations subforum.

In the absence of any particular interpretation, "collapse" is just the mathematical procedure we use to update our model when we know the result of a measurement, and no assertion is made at all about what, if anything, "actually happens".
yeah I know, that's why I told I was not satisfied with that answer
 
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