In quantum entanglement there is not known interaction between the entangled subjects.
Spin-orbit coupling or atom surface entanglement appears to me an unwarranted effort to promote already non intuitive concept of entanglement.
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- Thread starter arfa brane
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In quantum entanglement there is not known interaction between the entangled subjects.
Spin-orbit coupling or atom surface entanglement appears to me an unwarranted effort to promote already non intuitive concept of entanglement.
exchemist
Valued Senior Member
Yes that's why I'm a tad suspicious of the idea myself in contexts like that. But Arfa is no fool, so let's hear what he has to say.
He certainly is not, as I observed earlier in this thread and subsequently you also observed, that he had read too extensively on this subject, probably due to his interest in quantum computing, but he is not able to coherently set it together. His approach of accepting and attempting to fix all the text he has read as true is causing problem. Not his fault, the concept itself has the potential to accept weird chain of thoughts. That's why I suggested unlearning the unwarranted text.
Have you looked at the discussion at the physicsforum link I posted?exchemist said:
Interestingly, there is one forum member who also questions, like you're doing, what at least two other posters have to say about entanglement. The other two win the argument in my playbook, but you should have a look at it, it's only two pages.
This link should not be assumed to be the only evidence I've found that entanglement is very general, and it's a misconception to think it's only seen in the lab.
As to useful insights, I have no idea. I can't see what naming something can have to do with insights.
exchemist
Valued Senior Member
Yes I did look at the physics forum discussion but did not find it very persuasive. But then, it is only a discussion, rather than a setting out of a complete rationale.
As for the insights issue, I have a belief that the models we use in science need to serve a purpose in aiding understanding of how the world behaves. We often have more than one model to address a given physical situation or observed phenomenon. Based on what you have shown, I still do not see value in selecting the entanglement concept to account for spin-orbit coupling or chemical bonding (for example). I see it as a distraction rather than a help.
To return to specific instances of the above, you have yet to explain why you think entanglement is needed to account for why a solid is solid or what gives rise to friction, which you suggested were dependent on it. I have provided (post 360) the conventional explanation of both, as I understand them, in which entanglement does not feature. If you think I am missing something, as a result of overlooking entanglement, I should be grateful if you can indicate what it is.
Because, you see, that is what I am missing in everything you have written on this topic. You quote source after source but you seem unable to to show the value of the concept by applying it to specific instances.
Entanglement isn't something I think about as being "needed to account for" this or that state of some chunk of matter.exchemist said:
It's something I prefer to think about as being as fundamental as the Higgs field, say. Moreover, it isn't about the physics as such, it's about what observers know or can know about each other, pretty much.
But you do "need" the Hilbert space of complex amplitudes; it seems there are multiple ways to derive this fact (maybe that's interesting). It also seems interpreting QM doesn't seem to lead to much in the way of insights (many-worlds (?), hidden variables, pilot waves, . . .).
exchemist
Valued Senior Member
Well entanglement is a concept in physics and, as such, it is its job is to account for and predict observable phenomena. Which it does, very remarkably, in the case of spin-correlated particles at large separations.
It is fundamental if you take it to refer to all instances of combined QM states, since these are an intrinsic feature of QM, in a number of contexts.
Complex wave function amplitudes and state vectors in Hilbert space are mathematical features of QM which help to enable the model to make its vast array of of successful predictions.
As for "interpreting" QM in terms of many worlds and all that, I gave up on all that many years ago. The model seems so far to pass every test set for it. I do not aspire to be the next Enstein. Someone will come along in due course, probably after I am dead.
A possible recap of entanglement.
Write "up" on one piece of paper and "down" on another. Put each paper in an envelope and post one to London and the other to New York. On opening the envelope in New York, if the paper has "Up" on it then you know 'instantly' that the paper sent to London has "Down" written on it. The envelopes can be opened in any order and at any time and one observation will be sufficient to determine what the other envelope contains.
For entangled (say) photons it is an act of faith (on my part) that the up/down wasn't predetermined at the time of entanglement. I justify my faith that the up/down isn't determined at the time of entanglement by noting that the people making that claim are very clever and will have tested the possibility of predetermined outcome to the point that the predetermined outcome option is now generally discarded.
Write "up" on one piece of paper and "down" on another. Put each paper in an envelope and post one to London and the other to New York. On opening the envelope in New York, if the paper has "Up" on it then you know 'instantly' that the paper sent to London has "Down" written on it. The envelopes can be opened in any order and at any time and one observation will be sufficient to determine what the other envelope contains.
For entangled (say) photons it is an act of faith (on my part) that the up/down wasn't predetermined at the time of entanglement. I justify my faith that the up/down isn't determined at the time of entanglement by noting that the people making that claim are very clever and will have tested the possibility of predetermined outcome to the point that the predetermined outcome option is now generally discarded.
exchemist
Valued Senior Member
That fits my understanding of the term exactly.
BdS
Registered Senior Member
I don’t get it. When they are created they are a pair up and down, so when you open one up it’s obvious the other is down.
If you change the up to a down when it’s on route, does the other original down become up?
But, that's not quite right, is it?
Instead you don't write up or down on any of the 2 pieces of paper. Send them on their way. When you open one of them in either city, it will have either up or down written on it. Then you will instantly know the state of the other [edit -- added] when it is looked at[edit-- added].
To assume/project the outcome of the state before it is measured can not work.
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Nacho: You make important points! Entanglement is basically a logic experiment IMO. IF true entanglement occurs regardless of the original relational state (co-condition) of each of two entangled entities are known, a change in condition of one entity will necessarily change the condition of the remaining paired (entangled) entity.
I'd philosophically refer tothe options as "passive" enganglement vs "active" entanglement. An example of the former (passive) might be pre-printing the two envelopes - one says up and the other says down. Opening them at their respective destinations will not change the state of either - and the opened state is the the same as the orignial state for both - up in one and down in the other. These relative states DO NOT change, and indeed one can 'know' the state of the remote case when the local case is revealed - knowing the "rule" set up in the experiment initialization is required.
However, sending both envelopes to their respective destinations, with no understanding of the initialization "rules", (i.e., they can have either up or down emplazoned) or different experimenters individually (without knowledge of the other's choice) choosing to label each up or down will reduce the state of both entities to probabalistic endeavors. This resultcould also be circumvented if the individual experimenters communicate after the delivery events and share their initializations. In this case, the entanglement would not be primary , but rather secondary . . . IMO, of course!
There are likely other experimental setups/solutions that would mimic entanglement, but NOT actually be entanglement. After-the-fact (envelope delivery) changing of one condition (up or down) on one of the envelopes would NOT change the original condition of the remote envelope, IMO. of course.
I'm sure I have not explained my reasoning adequately (for me either!) . . . I'll have to study more thoroughly when I get some time! . . .later!
BTW: IMO, true entanglement, if not a simple logic argument, would require some extensable, instantaneous reactive media for communicating initial and final (choice) states (conditions) between the two entangled entities.
What's needed to refute the possibility of classical entanglement? Why aren't the contents of the two envelopes "mixed up" like qubits?
Pedantically, you could argue that the envelope's contents can't be in superposition, or exhibit any interference. Or in short, you can't write an equation that corresponds to an entangled pair of classical states--they're always in the wrong Hilbert space.
If, that is, the term entanglement is restricted to $$ \mathbb C^{2n} $$.
And you could argue that Shannon entropy (of the contents of classical envelopes), is a subset of von Neumann entropy. The latter is an entanglement measure as well as quantifying quantum/classical information content.
Pedantically, you could argue that the envelope's contents can't be in superposition, or exhibit any interference. Or in short, you can't write an equation that corresponds to an entangled pair of classical states--they're always in the wrong Hilbert space.
If, that is, the term entanglement is restricted to $$ \mathbb C^{2n} $$.
And you could argue that Shannon entropy (of the contents of classical envelopes), is a subset of von Neumann entropy. The latter is an entanglement measure as well as quantifying quantum/classical information content.
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That's interesting karenmansker. I've never heard of "passive" VS "active" entanglement. I'd like to hear more when you get time.
I think there are other things in this "envelopes being sent to New York & London" scenario, that needs to be considered or pointed out to fully and adequately demonstrate the outcome of entanglement measurements. Some I thought of are:
1) The person sending the envelopes and the 2 persons reading the envelopes are all different persons.
2) It cannot be known which of the persons in New York or London will open their envelope first.
3) When the person in New York reads their paper they then know what the state of the paper in London will be IF (but not WHEN???) it is read.
4) Same for the person in London.
5) The only way the person in New York or the person in London will know for sure that the letter in the other city was received and opened is if they contact the other person, latter.
I think there are other things in this "envelopes being sent to New York & London" scenario, that needs to be considered or pointed out to fully and adequately demonstrate the outcome of entanglement measurements. Some I thought of are:
1) The person sending the envelopes and the 2 persons reading the envelopes are all different persons.
2) It cannot be known which of the persons in New York or London will open their envelope first.
3) When the person in New York reads their paper they then know what the state of the paper in London will be IF (but not WHEN???) it is read.
4) Same for the person in London.
5) The only way the person in New York or the person in London will know for sure that the letter in the other city was received and opened is if they contact the other person, latter.
But it doesn't. True entanglement is a measurable and replicable state of real world entities, nevertheless: there is no such medium, no such communication takes place as far as anyone can determine even theoretically, there is only one initial state "between" the "two entities", and so forth.
You could also, rather than rely on faith, run through the violations of Bell's theorem that have been experimentally verified - repeatedly, in dozens of different contexts, with many different kinds of entities, now over distances of hundreds of light years (so that the predetermination would have to have been set up to look like entanglement to us, now, hundreds of years ago).
One way to check would be to determine whether Bell's Theorem held for such mailings - if it does, they aren't "mixed up like qubits", but in some other way.
Whether you want to refer to their Bell's Theorem governed correlations as "classical entanglement" is up to you, but I would find it confusing and likely to cause mental errors. Reserving the term "entanglement" for the fundamentally different Bell's Theorem violating quantum situations seems prudent, to me.
Spin-orbit coupling, or why it's perfectly sensible to call it entanglement between the spin and orbital momentum of a single particle.
Roughly, spin-orbit coupling is the interaction between the spin magnetic moment of an electron and the nuclear magnetic field. But the nuclear magnetic field is something that exists for the electron, because in the electron's frame the nucleus is orbiting around it. This is entanglement because there are two "observers" of the total angular momentum, there are two Hilbert spaces.
Roughly, spin-orbit coupling is the interaction between the spin magnetic moment of an electron and the nuclear magnetic field. But the nuclear magnetic field is something that exists for the electron, because in the electron's frame the nucleus is orbiting around it. This is entanglement because there are two "observers" of the total angular momentum, there are two Hilbert spaces.
Do measurements of spin orbit couplings violate Bell's Theorem?
Well. That means you're implying a third observer, right?iceaura said:
Apart from the nucleus and the electron.
Once more with feeling, lads. This is a game of two halves. (two inseparable Hilbert spaces, I should say)
Why it's sensible to say the two emerging beams from a Stern-Gerlach apparatus are spin-polarized. Why it's also sensible to say each beam is spin-position entangled.
It's because if you measure the spin of either beam, it's 100% correlated (up to uncertainty or quantum noise) with the position of that measurement.
Why it's sensible to say the two emerging beams from a Stern-Gerlach apparatus are spin-polarized. Why it's also sensible to say each beam is spin-position entangled.
It's because if you measure the spin of either beam, it's 100% correlated (up to uncertainty or quantum noise) with the position of that measurement.