What is the *DETECTOR* in the double slit experiment and how does it work? Is the detector a passive device or is it just a fictional mathematical probe.
I think the detector is somehow consuming the energy responsible for the wave nature of the photons, electrons or atoms, but I can't find any information about the detector and how it works.
Any help is appreciated since all videos and articles suspiciously skipping the detector or  simplifying it as a 3d cat or fictional cartoon eye.
I know about the quantum eraser experiment but before moving to it, I need to know about the detector and how it exactly measures.
I'm a software programmer trying to understand how quantum computers work.
 A: I misunderstood your question at first.  I thought you were asking about the detector downstream of the double slit, where the interference pattern is visible; every practical double-slit experiment includes such a detector.  But instead you are asking about a hypothetical detector which could "tag" a particle as having gone through one slit or the other.   Most interference experiments do not have such a detector.
The idea of "tagging" a particle as having gone through one slit or the other, and the realization that such tagging would destroy the double-slit interference pattern, was hashed out in a long series of debates between Bohr and Einstein.  Most introductory quantum mechanics textbooks will have at least some summary of the history of these discussions, which include many possible "detectors" with varying degrees of fancifulness.
A practical way to tag photons as having gone through one slit or another is to cover both slits with polarizing films.  If the light polarizations are parallel, it's not possible to use this technique to tell which slit a given photon came through, and the interference pattern survives.  If the light polarizations are perpendicular, the it would be possible in principle to detect whether a given photon went through one slit or the other; in this case the interference pattern is also absent.  If the polarizers are at some other angle, it's a good homework problem to predict the intensity of the interference pattern.
A: I watched a couple videos on the double slit experiment and I had exactly the same question as the original poster (Amr Berag) and stumbled upon this post and was just wondering how come everyone else isnt wondering the same thing.
There are so many videos showing the actual double slit experiment but none show the actual wave function collapse in reality when the particles are "observed".
It turns out that it was merely a thought experiment when it was first proposed and its not super trivial to put an actual detector, but in 1987 an experiment was performed and subsequent experiments were performed but none shown on video.
This link explains that a bit
Please look at the which way section here
I'm just surprised that they don't mention this in any of the videos and how come no one else asks for proof for this. When I saw the original video I was just waiting till the end to see them put a "detector" and see the interference pattern disappear, but nope.
A: It's anything that gives you information about where the particle passed by. The problem in measurement in QM is that to measure anything you need to interact with the "thing" you want to measure. If you want to measure temperature in a drop of water with a large thermometer, the heat of the thermometer will affect the drop temperature. If you want to measure the distance to the moon you may shoot a laser (knowing c=the speed of light in vacuum) and wait till it return. But if the smallest thing you have is rock, you can throw it and do the same process knowing the rock speed (ignoring gravity and air resistance), but if the smallest thing you have to measure it is another moon, you will affect the position of the "original" moon and so affecting the whole state of the thing you want to measure. Well, the quantum world is so small that to measure things you have to destroy the original state or perturb it. The device in the double slit is just to block or interact with the particle passing through that slit.
