Collapse of Wavefunction, Double-Slit Experiment

In summary, the conversation discusses the concept of wavefunction collapse in the double slit experiment and the role of measurement in this process. It also raises questions about the coherence of the particle and how it affects the experiment. The concept of interference and its relationship to measurement is also mentioned. The conversation concludes with a suggestion to refer to a quantum mechanics analysis of the experiment for further understanding.
  • #1
crissyb1988
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Now I'm trying to imagine the wavefuction before and after collapse when measured at either slit. Before the particle enters the slits I imagine the wavefunction more as a planar wave with no definite position (single wavenumber and a superposition of positions). If no measurement is made then our particle acts similar to a water wave when it comes to the two slits. It has a very definite wavenumber and hence it can constructively/destructively interfere with itself. If a measurement is made at either slit the wavefunction collapses to a very definite position (either slit A or slit B). This collapsed wavefunction is still a wave, but diffraction or interference would be almost impossible to detect as we now have many spatial frequency components. Do we know why the act of measurement simultaneously collapses the WF to a definitive position, whilst increasing its wavenumber components? Can we think of the particle pre-measurement as "coherent" and post-measurement "de-cohered", I'm confused as how coherence plays a role in the single particle experiment?

Also..If, after the collapse of the wavefunction, we let the particle propagate would it spread out over time due to the Schrodinger Equation?

Hope this makes sense!
 
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  • #2
crissyb1988 said:
... If no measurement is made then our particle acts similar to a water wave when it comes to the two slits. It has a very definite wavenumber and hence it can constructively/destructively interfere with itself. If a measurement is made at either slit the wavefunction collapses to a very definite position (either slit A or slit B). This collapsed wavefunction is still a wave, but diffraction or interference would be almost impossible to detect as we now have many spatial frequency components. Do we know why the act of measurement simultaneously collapses the WF to a definitive position, whilst increasing its wavenumber components? ...

The classical picture will have problems. We can place polarizers in front of each slit to gain information about the photon. When they are parallel, there will be interference and the associated pattern. When crossed, there will be no interference and just the 2 bar pattern building up.

So there is not the kind of collapse you are envisioning (to a point particle).
 
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  • #3
crissyb1988 said:
This collapsed wavefunction is still a wave

Hmmm

You may be confused about a few things.

There is no collapse in the double slit experiment because the photon etc is destroyed.

You may want to check out an QM analysis of the experiment:
http://arxiv.org/ftp/quant-ph/papers/0703/0703126.pdf

Thanks
Bill
 

Related to Collapse of Wavefunction, Double-Slit Experiment

1. What is the collapse of wavefunction in the double-slit experiment?

The collapse of wavefunction refers to the phenomenon in quantum mechanics where the probability wave, or wavefunction, of a particle collapses into a single state when it is observed or measured. In the double-slit experiment, this means that the particle's position and momentum are determined once it is observed at the slits.

2. How does the double-slit experiment demonstrate the collapse of wavefunction?

In the double-slit experiment, a beam of particles is passed through two parallel slits and projected onto a screen. When the particles are not observed, they behave like waves, creating an interference pattern. However, when observed, the particles behave like individual particles, creating two distinct bands on the screen. This demonstrates the collapse of wavefunction as the particles' wave-like behavior disappears when they are observed.

3. What causes the collapse of wavefunction in the double-slit experiment?

The collapse of wavefunction is caused by the interaction between the observer and the particle being observed. When the observer measures the particle's position or momentum, they are essentially interacting with the particle and collapsing its wavefunction into a single state.

4. Can the collapse of wavefunction be explained by classical physics?

No, the collapse of wavefunction is a phenomenon that can only be explained by quantum mechanics. In classical physics, particles are assumed to have definite positions and momenta at all times, whereas in quantum mechanics, the position and momentum of a particle are described by a wavefunction that collapses upon measurement.

5. Are there any alternative explanations for the collapse of wavefunction?

There are various interpretations of the collapse of wavefunction, such as the Copenhagen interpretation, which states that the collapse is a fundamental property of quantum systems. Other interpretations, such as the many-worlds interpretation, propose that the wavefunction does not collapse, but rather branches into multiple parallel universes. However, there is currently no consensus among scientists on which interpretation is the most accurate.

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