| If you ever ran into a space leak in Haskell, you would see how having unresolved thinks can use more memory than eager evaluation. But that has some merit to it in that you can describe QC as merging equivalent paths and then sampling from a wave distribution afterwards. One fun variant on the double slit experiment is taking a coherent laser beam (everything is in phase) and splitting it, sending it through two paths, A and B, then merging it and shining it on the wall. If the two path lengths are equal, there is no effect from splitting it. But if we make B take slightly more time we can get a interference pattern. If we have it get shifted by half a wavelength the light will cancel out! Now if you insert a polarizing filter along path B, when you merge the streams, you could tell with path the light came from, and the interference pattern disappears. This is not exactly measuring which path it took, but making it possible if you added a sensor to tell. Observation is not required just making the streams distinguishable. But now if we add another polarizing filter downstream we can erase the distinction between them, and now you get interference effects again! |
If the slit A has no polarizer and slit B has a polarizer, then in the "wall" you will the sum of 50% of the interference pattern and 50% of the diffraction pattern of A(I'm not sure about the 50%-50% split, something like that.) I.E. you will see the interference pattern, but it will not be so sharp, the black lines will not be so black, the white lines will not be so white.
I think it's better to put an horizontal polarizer on A and a vertical polarizer in B. If you don't add any other polarizer you will see the sum of the diffraction patters of A an B, without interference lines.
If you put a polarizer, the result depends on the direction:
* If it is horizontal you will see only the diffraction pattern of A (without interference lines).
* If it is vertical you will see only the diffraction pattern of B (without interference lines).
* At 45° you will see the diffraction pattern like in the original double slit experiment.
* At the other 45° you will see the inverted diffraction pattern, the black lines will be white and the white lines will be black. (All of this bounded by the diffraction pattern.)
* At other angles, you get some mix of the diffraction patterns and the interference patterns.
It would be nice to see an experimental realization of this.