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Considering (again!) which way type of experiments (the interference type of set ups when a photon may go through two different routes and then one recombines the paths and checks for the presence of absence of interference (as used in quantum erasers, etc)).
Usually, people say that if there is no way to detect the path taken by the photon, there will be interference.
But I am bothered by the mirrors in the experiment. Don't they act as some kind of measurement device? (even if we do not use them to detect the path of the photons)??
I mean, doesn't the mirror (one of them at least) ''knows'' whether the photon was reflected off from it?? I know this sounds silly, but it seems that for the photon to be reflected, it must interact with the atoms in the mirror, and that would seem to represent a type of microscopic measurement. Even if the mirror is perfect.
Pushing the argument further, what distinguished what we usually consider a measurement from what the mirror does by reflecting the photon (or not reflecting it...I am not sure what to think!)?
I mean, at waht point do we consider the interaction of the photon with a system a ''measurement'' which will lead to the lost of the interference pattern? There is something maybe about the irreversibility of the interaction with a measuring instrument that makes this qualititatively different from the interaction with the mirror...It is puzzling to me (but may be obvious to other people here).
Also, usually the distinction between interference vs non interference seems to be a yes/no issue... a ''digital'' question.
But can there be situations where the lost of interference is only partial? maybe 80% of the photons show no interference effects whereas the other 20% do... This would be possible if the intreaction with a measuring device would lead to a partial lost of information...
I know that this is very vague...But I hope someone(s) will help clarify or focus the discussion.
Thanks
Pat
Usually, people say that if there is no way to detect the path taken by the photon, there will be interference.
But I am bothered by the mirrors in the experiment. Don't they act as some kind of measurement device? (even if we do not use them to detect the path of the photons)??
I mean, doesn't the mirror (one of them at least) ''knows'' whether the photon was reflected off from it?? I know this sounds silly, but it seems that for the photon to be reflected, it must interact with the atoms in the mirror, and that would seem to represent a type of microscopic measurement. Even if the mirror is perfect.
Pushing the argument further, what distinguished what we usually consider a measurement from what the mirror does by reflecting the photon (or not reflecting it...I am not sure what to think!)?
I mean, at waht point do we consider the interaction of the photon with a system a ''measurement'' which will lead to the lost of the interference pattern? There is something maybe about the irreversibility of the interaction with a measuring instrument that makes this qualititatively different from the interaction with the mirror...It is puzzling to me (but may be obvious to other people here).
Also, usually the distinction between interference vs non interference seems to be a yes/no issue... a ''digital'' question.
But can there be situations where the lost of interference is only partial? maybe 80% of the photons show no interference effects whereas the other 20% do... This would be possible if the intreaction with a measuring device would lead to a partial lost of information...
I know that this is very vague...But I hope someone(s) will help clarify or focus the discussion.
Thanks
Pat