Q&A

Why is ther always two different ways to erase data? And never three? Is there any other way the have to pattern at -45 degree in experiemetn 6 than with polarizers?

This is super interseting. We put all those questions together becaus they refere to the same phenomenon. Let's agree that if we take a double slit, there is no way you can find the "invert interference". But when we add the polarizers in front of each slit and a third one after (experiement 5.3 or 6), we do get the two patterns.

The reason why we cannot get that second pattern with no polarizer is beacause we don't touch the beam. Every photons has the same state. Half goes through one slit, half through the other. There is nothing here that can change the state. So when they interfere with each other,the phase has to be 0.

On the other hand, when you add the polarizers, the phase will be changing. If you start with a beam at 45 degree, and one slit has a 0 degree polarizer and the other has one at 90 degrees, we can say we change the polarization of the initial beam by 45 degrees, rotating in different sens (on is clockwise, the other counter-clockwise). When we put a thrid polarizer, we again change the phase, let's say clockwise. The photon that were changed also clockwise completed half a turn, an the one that changed counter-clockwise returned to their initial state ( 0 turn). At the end, the result is that half of the photon has a phase of 180 degree compare to do other.

What if a fly look at the setup, would it again act like a quantum eraser? Who needs to look at the data?

what happens if only half of collected data is erased? Or can I collect only half the data?

blablabla

How come a single photon still create interference pattern?

Only a single photon cannot create aninterference pattern by itself. The interference pattern can appear if you send a lot of particle, even one at the time. The resulting will recreate an interference pattern.

To understand why, you need to stop thinking a photon is only a particle and see it as a wave. A wave can easily pass though both slit at the same time and interfere with itself.

Now you are going to say, if I put a detector in front of each slit, I will see the photon in either one of the slit. YES. But when you do place a detector, you make the wavefunction collapse and the photon start acting like a particle.

Does the experiment needs to be done in vaccuum? Can only dust particle make the wavefunction collapse?

If a photon hits a dust particle, it will bounce on the dust particle and deviate. The photon will never be capture by the tiny detectors. If you think about it, it isthe reason why you can "see" a laser beam when it is on, because some photons bounce on dust particle and reach your eyes.So there is no need to do the experiment in a vaccuum chamber, but it might incresea little bit the number of photon you can collect.
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What if you look at the data, confirm it behaved like a particle, and then erased the data? Would it go back to an interference pattern, or would the observation of the data before deleting it mean it would have to stay
as a particle?

blablabla.

Conclusion

Q&A

Similar Experiments

Overview

Polarizers

Single and double slit