# Double slits experiment with one or two detectors

#### Fox333

Let's try another variation of the experiment.
There is still only one detector in the left slit, but it can be randomly switched on or off. The observer can only see if the particle detected or not, he can't know if the detector's switched on or off. Also the observer can see the interference pattern or its absence after every attempt.

What we can get?
1) If the detector's switched off we will get the interference pattern.
2) If the detector's switched on and the particle passes throw the left slit we will get the particle detected and no interference pattern.
3) If the detector's switched on and the particle passes throw the right slit. This case is unclear for me. According to the video, we must get no interference pattern and no particle detected. But it leads to the conclusion that the observer breaks the wave without having any information about the particle's position, as long as he can't distinguish 1) and 3) until seeing no interference.

Any thoughts?

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#### kiwiheretic

3) If the detector's switched on and the particle passes throw the right slit. This case is unclear for me. According to the video, we must get no interference pattern and no particle detected. But it leads to the conclusion that the observer breaks the wave without having any information about the particle's position, as long as he can't distinguish 1) and 3) until seeing no interference.

Any thoughts?
If there is only one detector and two slits then that is enough to destroy the interference pattern. Even by being able to deduce which slit the other particle went through without actually measuring it is enough to provide "which way" information.

It seems to be the "which way" information (knowledge of which slit the particle through) that destroys the stripey (interference) pattern, not the detector. For instance if the which way information is deleted with a quantum eraser the stripey pattern is restored.

At the risk of confusing you even further I added the following video to show that even with the detectors present a stripey pattern can be recovered.