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What about the "DETECTOR". Is it a passive device or is it just a fictional mathematical prob. I think that detector is somehow consuming the energy responsible for the wave nature of the photons, electrons or atoms but i cant find eany information about that 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 is it exactly measuring. Im a software programmer trying to understand how a quantom computer works

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  • $\begingroup$ You can use a wall as a detector. $\endgroup$ – rob Mar 23 at 1:11
  • $\begingroup$ @rob I mean the detector that is supposedly causing the photones to change their mind and act as particles withot wave characteristics and not the surface $\endgroup$ – Amr Berag Mar 23 at 1:21
  • $\begingroup$ @rob Its somthing scientists said or imply they placed behind the slits to determine which slit a particular photon or atom went through before hitting the surface. Th surface hier is the wall you are talking about. $\endgroup$ – Amr Berag Mar 23 at 1:59
  • $\begingroup$ Oh, I see. I misunderstood your question. $\endgroup$ – rob Mar 24 at 4:28
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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.

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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.

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  • $\begingroup$ You just rephrased my question bro. Are you telling me that the detector in the double slit experiment is not passive enough to detect without afecting the outcome? Then why all these credited sientists jumping to the assumption that photones are conscious instead of saying that the very act of trying to detect is affecting these photones and particles in a way that they lose their wave characteristics by withdrawing their enrgy for example. Or do you mean the detector is nothing but another surface moving toward the slits but then it will be too close and prevent the interference! $\endgroup$ – Amr Berag Mar 23 at 1:47
  • $\begingroup$ I din't rephrase your question. There's no single question mark on my reply. The math is a model to represent a behavior that is very consistent. It is not passive enough $\endgroup$ – Gndk Mar 23 at 1:59
  • $\begingroup$ Do you mean there is no detector? $\endgroup$ – Amr Berag Mar 23 at 2:04
  • $\begingroup$ It is not passive enough to detect without affecting the outcome. That's why you can't measure (or get to know) both, position and velocity with infinite precision. Those Observables (X and P) are related in a way that measuring one will "destroy" the information of the other observable (same thing for L which I'v heard is what its measure in Q computation). The math is a model to represent a behavior that is very consistent. Which scientist jumped to the assumption that photons are conscious? What do you mean by consciousness? $\endgroup$ – Gndk Mar 23 at 2:14
  • $\begingroup$ Here's a related topic with links to videos and papers: physics.stackexchange.com/questions/297087/… $\endgroup$ – Gndk Mar 23 at 2:18

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