# Interpretations of quantum eraser experiment

1. Nov 21, 2009

### dave137

Hi

My interpretation of how observing the double slit experiment removes the interference pattern was that when (for example) an electron interacts with a photon, the electron is forced to be "at" that position, collapsing it's wavefunction. Then as the electron continues on towards the screen the probability of it going through the other slit is small or negligible from this location (in or next to one of the slits) and so no interference takes place. (this could be way off)

Having seen this though

http://www.scientificamerican.com/media/inline/DD39218F-E7F2-99DF-39D45DA3DD2602A1_p95.gif

I don't know what to think. If by using the magnefying glass the interference pattern can be restored then it's not so much the interaction with the photon, but the existence of certain information that destroys the interference pattern. Does the interaction even collapse the wavefunction as i doubt the collapsed wavefunction could be un-collapsed?

Is there a generally excepted interpretation of what is going on here? I assume that if the magnefying glass is placed far enough away so that the electron hits the screen before the photon reaches the magnefying glass then there is no interference pattern?

ps. I wouldn't have said that after a simple interaction like this the electron and photon would be entangled, but surely they must be here?

2. Nov 22, 2009

### RUTA

There are lots of proposed solutions to the measurement problem, none are accepted outside their small circle of proponents. You'll have to solve MP before you can solve quantum eraser.

3. Nov 22, 2009

### DrChinese

As RUTA states, the "true" picture is a matter of interpretation.

Collapsed wave functions can be recombined (thus restoring an earlier state)! An example would be sending an entangled photon "Alice" through a polarizing beam splitter, and then carefully recombining the 2 output paths so that knowledge of polarization is lost. The recombined Alice beam will still be polarization entangled with Bob.

Because the interpretations are mostly equivalent mathematical devices, most claim that such result is consistent with their interpretational assumptions.

4. Nov 22, 2009

### Neo_Anderson

One thing I can't figger out is this: With the quantum eraser, the interference pattern is lost when we shine light on the particles that create the interference pattern.
If this is so, then why do diffraction gratings still act like superprisms?

5. Nov 23, 2009

### dave137

Okay. I can't do the maths for the double slit experiment, but i know it qualitatively, either by working out the probabilities of each path or using Feynman's sum over paths method and i can imagine some picture of what's going on, how interference occurs. (i've not studied dynamic systems like this, only harmonic oscillators or potential wells)

Is there a mathematical solution to this experiment? So that i can try and interpret that, i'm happy to learn new maths but if it's the whole of QED or anything then obviously i don't expect anyone to explain it all to me.

Thanks