Quantum Mechanics: Understanding Particles at a Distance

[Nugatory]

Its just when people say that they performed an entanglement experiment and got results in agreement with predictions, the ones listed above are no-where near the QM prediction.

Which people? If you don't go back to the original publication, you're hearing a conclusion while seeing neither the original results nor the steps by which the results are said to support the conclusion.

 

[jk22]

I appreciate that you see it as 2.82, but Wineland's team has a different value for their setup. As I say, each setup has different issues and you should not compare one directly to the other. Although you are determined to do that anyway...

My question then is how do they calculate the value for their setup ? Reading Bell's original work shows 2 things : local realism limits CHSH to 2, and QM gives 2.82 as prediction.

I found no trace of a theoretical calculation to obtain 2.37 in that experiment.

The thing that disturbs me is that 2.82 corresponds to prediction with certainty along the same axes, following EPR, whereas 2.37 does not imply such a fact.

 

[StevieTNZ]

Yes, I'm confused as well with this. I'm desperately trying to understand this matter myself.

 

[jk22]

The result 2.82 permits a prediction with certainty, whereas 2.37, since the covariance is also a cosine curve, doesn't.

Why bother about that prediction capacity : this is to find back in 1935's EPR paper :

EPR set up a criterion (without any proof) that if you can predict with certainty there should exist elements of phys. reality.

Bell quantum calculation permits such a prediction with certainty, so in the sense of EPR there should exist elements, but those are not the Bell's element lambda.

The latter point was proven by Wineland's experiment for example since CHSH is bigger than 2.

But this experimental result goes further : we cannot predict with certainty, hence following EPR there is no reason to believe there are elements of reality, the criterion for existence is not anymore fulfilled.

 

[DrChinese]

My question then is how do they calculate the value for their setup ? Reading Bell's original work shows 2 things : local realism limits CHSH to 2, and QM gives 2.82 as prediction.

I found no trace of a theoretical calculation to obtain 2.37 in that experiment.

Not quite correct. 2 is the upper limit for any local realistic (LR) theory, as you say. But 2.82 is the upper limit for QM, not the prediction. So a measured value of 2.3 rules out LR and validates QM.

Any pair which reaches the detectors but has experienced decoherence on the polarization basis serves to eat away at the actual rate and cause it to be lower. This can be estimated in advance, as calibration is occurring. For example, in Weihs et al, they obtained 97% visibility during that phase. Therefore they expected a result of about 2.82 * 97%, or 2.74. The experimental value was 2.73 +/- .02, in good agreement. See after their (1).

http://arxiv.org/abs/quant-ph/9810080

I realize it bothers you that some authors do not explain specifically how they arrived at their expected values, but this is more a matter of editing than anything else. The actual information to arrive at 2.37 is in the Wineland article for anyone who is interested.

Hint: (.88 - (2*.02)) * 2.82 and I will let you find and figure that out for yourself.

 

[DrChinese]

But this experimental result goes further : we cannot predict with certainty, hence following EPR there is no reason to believe there are elements of reality, the criterion for existence is not anymore fulfilled.

This statement is completely wrong. "Element of reality" is actually a requirement of the Bell proof. And the EPR criteria IS fulfilled experimentally in Bell tests is demonstrated, just not to 100% accuracy. 100% accuracy is not a requirement for any experiment.

What is not demonstrated is that there are *simultaneous* elements of reality. EPR discusses this point as well.

 

[jk22]

i don't mean the accuracy for prediction power. What I mean is that 2.37(prediction is not exact) is MORE accurate than 2.82, where prediction is exact.