Entangled particles

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  • #26
jfizzix
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If there are two entangled particles, and one of the pair is annhiliated, what, if any effect will it have on it's entangled partner??? Thanks
There will be no effect on the entangled partner.

There is no way of knowing whether a single particle is entangled with something else, without getting information from that something else. Correlations can change following annihilation, but the marginal statistics do not.
 
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  • #27
phinds
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If there are two entangled particles, and one of the pair is annhiliated, what, if any effect will it have on it's entangled partner??? Thanks
The state of the entangled characteristic of the non-annihilated particle will become "known" in the sense that IF the annihilation "measures" the character of the particle as it is being annihilated (which I think has to be the case), AND you can "catch" that value, AND you were to travel to where the other particle is and measure its characteristic you would find that it is what you would expect it to be based on the value of the annihilated particle
 
  • #28
TTIDCOYS
Thanks!!!
 
  • #29
morrobay
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I have some questions about quantum entanglement



Now... Why is this considered bizarre? Why can't we just realize that the two electrons had their spins already set up in the state we later would find them to be in? To be more precise, I will give an example

Before destroying the molecule:
Electron 1 has spin up in z direction
Electron 2 has spin down in z direction

Of course, calling "Electron 1" and "Electron 2" is just to keep things clear, afterall they are indistinguishable particles.

Suppose further we don't know these are their spin states. When the electrons got separeted, it seems obvious that their spin states will keep in that way. In other words, there is nothing bizarre happening, it is just we did not know what their spin state were.
Everything seems normal , realism, CFD ,when spins are measured along parallel angles at spacelike separated detectors A and B: producing this data set :
detector A detector B
x y z >>> x y z
+ + + >>> - - - n1
+ + - >>> - - + n2
+ - - >>> - + + n3
- - - >>> + + + n4
- - + >>> + + - n5
- + + >>> + - - n6
- + - >>> + - + n7
+ - + >>> - + - n8
So from here you could logically say n(y+x-) + n (z-y+) ≥ n(x+z-) , (n1,n2) + (n3,n4) ≥ (n1,n8).
But this inequality does not hold when detectors are not aligned
 
  • #30
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One can make entangled pairs of photons in the lab by Spontaneous Parametric Down-conversion. These entangled pairs of photons have been shown to have position and momentum correlations strong enough to violate a conditional uncertainty principle, demonstrating the EPR paradox.

http://www.pas.rochester.edu/~jhgroup/papers/schneeloch-prl-13-01.pdf

One can also perform similar experiments to close the locality loophole as well

https://arxiv.org/ftp/arxiv/papers/1111/1111.0760.pdf
I have no problem at all with the results of measuring entangled photons. If A and B measure along the same axis they will get the same result.

Now if A measures along axis α and gets result 1, while B measures along axis β and gets -1, then what EPR said (to claim HUP was violated) was that B's α value is thus 1. That is, if B had measured along axis α instead he would have gotten value 1.

Bohr disagreed, saying, to the effect, that experiment (A and B measure along α) wasn't made. If we make that experiment it might happen that A and B both get value -1. The assumption that in the initial experiment that B has an α value is CFD/realism, (see post #19) a classical and very intuitive assumption.

Bohr and Einstein died before Bell resolved the issue, showing Einstein's assumptions were invalid. How I would have loved to hear Einstein's response.
 
  • #31
entropy1
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Before destroying the molecule:
Electron 1 has spin up in z direction
Electron 2 has spin down in z direction
[..]
Suppose further we don't know these are their spin states. When the electrons got separeted, it seems obvious that their spin states will keep in that way. In other words, there is nothing bizarre happening, it is just we did not know what their spin state were.
I might add to my previous response: if (the spin direction of) electron 1 gets measured, then the probability electron 2 measures the opposite spin of that spin, is dependent on the angle between both detectors. This is a non-local property of entanglement, for it is dependent of both the properties of the separate detectors. You could also see it like this: if the angle of detector A is α, and it measures 'spin-up', then electron 2 'behaves' like its spin is along the basis of detector A (α). That is, electron 2 did not have a fixed spin (hidden variable), but behaves as if its spin got determined by detector A. This works vice-versa.
 
  • #32
morrobay
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I might add to my previous response: if (the spin direction of) electron 1 gets measured, then the probability electron 2 measures the opposite spin of that spin, is dependent on the angle between both detectors. This is a non-local property of entanglement, for it is dependent of both the properties of the separate detectors.
Yes and the probability for opposite spins : P-+ = P+- = 1/2 ( cos θ/2)2 That are dependent on both detector settings , θ = β - α
What are the alternative explanations for the correlations between spacelike separated entangled particles that do not include a superluminal signal ?
In this paper http://www.mathpages.com/home/kmath731/kmath731.htm and elsewhere are the terms:
1. " QM non separability"
2. Correlations " encoded during preparation of entanglement .
Then how are 1 and 2 in accord with P++ = P-- = 1/2 (sin θ/2)2 that imply a dependence on detector settings A and B for the distant correlations that violate Bell's inequality , but again do not include superluminal signals ?
 
  • #33
entropy1
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What are the alternative explanations for the correlations between spacelike separated entangled particles that do not include a superluminal signal ?
Non-CFD/non-realism might be one I guess.
 
  • #34
entropy1
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Non-CFD/non-realism might be one I guess.
However, the detection of a photon or elektron doesn't contain/reveal the angle of, or between, the detectors, and as such information about the angles isn't part of the measurement. Rather, it is revealed in an ensemble. It means that a single measurement could just as well have been local what information is concerned. Verifying if it was local, requires locality (bringing the results together), so that locality is not violated. The one locality is as it were replaced by the other; if you make the results local, the experiment is no longer required to be local, which is what we observe.
 
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  • #35
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There is no way of knowing whether a single particle is entangled with something else, without getting information from that something else. .
This one is bending my mind (it is probably supposed to). If you are to get information from the something else, you need to know what the something else is and probably where it is (which puts us into red green sock territory). Presumably if a particle is entangled with something else, and is going to respond when the state of that something else changes, there must be something in the particle that 'knows' which something it is entangled with.
 
  • #36
DrChinese
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This one is bending my mind (it is probably supposed to). If you are to get information from the something else, you need to know what the something else is and probably where it is (which puts us into red green sock territory). Presumably if a particle is entangled with something else, and is going to respond when the state of that something else changes, there must be something in the particle that 'knows' which something it is entangled with.
You really don't get any information. It's random and essentially redundant.
 
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  • #37
entropy1
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You really don't get any information. It's random and essentially redundant.
I don't immediately agree with that: when data from 'the other side' is added, we have information about the relative orientation of the detectors, right?
 
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  • #38
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I should not have used the term 'information', I was addressing the post that I quoted. Certainly 'you' don't get anything. The second part was really my 'philosophical' question which is that if a particle is going to respond to something that happens to its entangled particle 'it' must 'know' which particle to respond to.
But that's probably getting off topic.
 
  • #39
morrobay
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Non-CFD/non-realism might be one I guess.
Yes since the inequalities are derived from CFD: From spin 1/2 particles the strict anti correlations along parallel settings enables you to deduce
A+B- , A-B+ for one pair of particles and
A+C-, A-C+ for another pair. Leading to this general form of Bell inequality: N(A+B-) + ≤ N(A+C-) + N(B-C+)

And for the CHSH inequality : (AB) + (AB') + (A'B) - (A'B') ≤ 2 A,A' B,B' = ± 1
However in the just closed thread; Quantum entanglement information. Post # 43 ,
@Mathematech states that CFD is an invalid assumption when there are more than two variables.
Quote: (selected) "The point of particular importance is the idea of combining counterfactual results with factual results gives the same statistics. It is a mathematical fact that when the counterfactual results are possible alternate results that were not obtained due to an incompatable experiment being performed instead, then when more than two variables are involved, the statistics need not be the same as a scenario where the counterfactual results were not obtained "

I would like to see an elaboration on the above claim that CFD is not valid for
the two inequalities above that results in the violations
 
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  • #41
entropy1
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What are the alternative explanations for the correlations between spacelike separated entangled particles that do not include a superluminal signal ?
I would like to see an elaboration on the above claim that CFD is not valid for
the two inequalities above that results in the violations
What I ment was that, as long as one of the two measurements is not examined, there is no need for a superluminal signal. If and when that other measurement will be examined, it will already be a non-superluminal course of events.
 
  • #42
DrChinese
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While I have great respect for Hess and Michielsen and the teams they are a part of: a) this is not a suitable reference; and b) it is far off-topic. The primary objective of their work is to produce mathematical models that can reproduce local realism in various respects.

This is a "B" level threat about quantum entanglement, not about arguing for or against local realism. You should start a new thread if you wish to go in that direction.
 
  • #43
PeterDonis
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This thread has run its course and is now closed.
 

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