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How is quantum entanglement observed? 
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#1
Jul3110, 10:57 AM

P: 24

Any measurement device used to witness the phenomenom seems like it would disrupt quantum entanglement. How do scientists manage to observe it?



#2
Jul3110, 07:01 PM

P: 18

One of the big experimental problems with entanglement is that it is very hard to directly check if you have an entangled state until you actually use up the entanglement. (and even then it's usually a problem for a single system). If you do have some other entanglement which you can "trust" it is possible to make a nonlocal measurement such as a bell measurement (not to be confused with the bell inequality) to verify if your system is entangled, this is very hard to do in experiment. What you need for that is an entangled measuring device which lets you record the modular sum of the spin in the X and Z directions. 


#3
Aug110, 07:40 AM

PF Gold
P: 1,662

If the photon pairs are not entangled – you will have 100 random measurements of (0, 0) or (1, 1) or (1, 0) or (0, 1). (Note: To get real violation of Bell Inequalities, you need to do more measurements on all relative angles, not only parallel.) P.S. There is something called Entanglement swapping where Quantum teleportation is used to entangle particles that never interacted with each other! 


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