Testing Quantum Entanglement...

Discussion in 'Physics & Math' started by Seattle, May 30, 2017.

  1. Seattle Valued Senior Member

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    If anyone here knows, how is quantum entanglement testing done? For instance, it is said that two entangled particles could be far apart, as in light years apart and their entangled state would still be intact.

    There is some discussion that information could be exchanged at rates faster than the speed of light. I've seen discussion that dissects the possibilities and shows that it can't be done.

    However, how is the claim backed up that two entangled particles can remain entangled even though they are light years apart? No one is able to separate an entangled pair by light years so is this just extrapolating from much smaller distances?

    In other words, is it just that the testers know of nothing that should unentangle the particles even should they be light years apart?
     
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  3. karenmansker HSIRI Banned

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    I don't know how the experiments are done. But I will hazard an OPINION (IMO) that if (in an experiment) quantum entanglement (by whatever method) is confirmed (by whatever method) between a pair of (then-entangled) particles, that entanglement-produced action on both interacting (entangled) particles would persist intact UNTIL some other interaction (e.g., subquantum, quantum or Planckian, or other force interaction) occurred with one of the particles and not the other particle. Then, the original entangled state (between the 2 particles) would be at least changed (or perhaps lost). In such an event (one such post-entanglement interaction with one of the particles) the second (un-interacted) particle would be unchanged by the other particle's interaction. The hypothetical 'spooky action at a distance' (non-local action) would NOT be seen - in which the action of the interacted particle would influence the non-interaction of the other particle. Just simple Newtonian (and force interaction) stuff, IMO. The unimpeded action at a distance condition will persist until that condition is 'interferred-with'. Then, unless the nature of the post-entanglement interaction (interference) is fully describable, or that interactive action equally affects both particles, the state of the remote (interacted) particle cannot be accurately predicted (known). All contrary notions are mathematical constructs that would remain unproven. All of the foregoing . . . . IMO, of course! HSIRI
     
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  5. Nacho Registered Senior Member

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    Well, I'll go out on a limb here. I hope someone that knows more will follow up.

    Q: How can you test for and agree about quantum entanglement:

    I don't think you can do it with, say 2 particles, both of which were so-called "entangled". I think you can do it only by statistical analysis of an ensemble of particles that SHOULD be entangled, to see if the analysis of that data AFTER the test is performed leads to the conclusion that there were coincidences between particles.

    Take the Alain Aspect experiments, the best page I could find on a short search that said anything about the setup of the experiment:


    https://www.revolvy.com/topic/Aspect experiment&item_type=topic


    This is for testing out the EPR thought experiments. He had a device that recorded particle coincidences from both channels of an (particle entangled) optical device. To call it a coincidence (entangled pair), there had to be particles entering his recorders (on either side of the experiment) within a predetermined time window. If there was a "hit" outside the time window it didn't count as a "hit".

    The detectors were not 100% efficient, so there was a discrepancy between the pairs that were supposed to be created VS the pairs that were detected.

    The 2 points I wanted to make:

    1) In practice, the devices to test for entanglement are not 100% efficient.

    2) He could only assume he detected an entangle pairs by using statistical analysis, i.e., because of the time window and not-100% effiency.


    I hope somebody that knows about how quantum computers are supposed to work will answer, and show how they know that multiple particles that were supposed to be in a superposition of states are now collapsed into a definite state.

    In general, I'd like to know if anybody knows of any experiment that can achieve results on just 1 (and only 1) quantum particle, VS getting results on an ensemble of particles.
     
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  7. karenmansker HSIRI Banned

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    Nacho: Thanks! Your analysis is likely correct, having done more source research than I.

    I find that there is much in the realm of theoretical (hypothetical?) physics that is more mathematical/statistical inference, and wishful conclusions from biased data, than is confirmed truth.
     
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  8. Nacho Registered Senior Member

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    Well, I haven't done any RESEARCH research .. just reading books and the like, but yeah. I agree somewhat. They call it "quantum", as in SINGLE particle mechanics, but I don't see anything to where results on single particles are being shown. It seems to me it is always averages or statistics of an ensemble of particles.
     
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  9. karenmansker HSIRI Banned

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    Yes, there is some misunderstanding IMO regarding usage of the term 'quantum' since quantum theory seems to deal with processes that may not be (yet) quantifiable and much of such 'research' deals with mechanisms/processes that are 'below-the-screen' mathematically and physically. My usage is that 'quantum' deals with discrete quanta (e.g., photons, other quantizable entities, etc.) and particles/processes that can be measured. I usually refer to anything smaller than Planck (length) as subquantum or subplanckian - I am sure that many out-there will disagree with my usage. I am a firm believer in subquantum processes and mechanisms and perhaps subplanckian 'particles', waves, etc. All that I've seen on such subquantum 'critters' is mainly relegated to mathematical and statistical constructs, virtual particles, and so on. Current math only works relatively well to somewhat slightly above Planck. It would appear (on practical grounds) that if science cannot 'detect'/observe/measure an entity (due to scale/size), then perhaps it does not/cannot exist (cannot be proven or quantized). This will change with time and development of interactive (or inferrable) detectors - perhaps harmonic-like or field oscillators (e.g., Casimir Effect) - that are capable of seeing beyond (smaller than) Planck length and at much higher resolutions. But I ramble on . . . . . later! Thanks for your reasonable discussions!
     
  10. danshawen Valued Senior Member

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    Observing the state one of an entangled pair of particles, however distant from its quantum entangled twin, means that the entangled twin will instantly assume the opposite entangled state.
     
  11. Nacho Registered Senior Member

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    Thanks karenmansker! I've read your posts, and I always considered them reasonable. Let me ask you a question: Do you consider diffraction to be in the realm of quantum mechanics, or maybe more appropriately "a quantum event"? I do, as just about anything w/o a classical description I place into the realm of quantum mechanics. Maybe there is another realm though that it should go in, and that "quantum mechanics" has a more specific definition than "not-classical". Just wanted to know how others viewed this. (I'm getting way off topic here, and promise not to go any further).
     
  12. Nacho Registered Senior Member

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    Doesn't that though go too far, and suppose there is a cause/event associated with the first measurement? I don't think it is known that there is a cause/event on the twin particle, at measurement time for the first particle.

    Shouldn't that more appropriately be: "When observing the state of one of an entangled pair of particles, however distant from its quantum entangled twin, means that the entangled twin will show the opposite entangled state whenever it is found/measured".
     
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  13. Seattle Valued Senior Member

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    My take on quantum physics is that it's referring to discrete energy states as opposed to a continuum (as far as the name, particle vs wave or discrete energy states of the electron in a atom).

    My other take on this subject is that it works well in terms of its predictions in a practical sense. Why it works or what is actually going on isn't known and that's why there are so many "interpretations".

    It's hard to say whether it's simply a mathematical construct or physical reality since what we are talking about is too small to see. It could be either.

    The way I chose to "interpret" (just as a layman) is that it's much like General Relativity. Newtonian physics works for most things in our everyday lives but GR still applied but on a scale that is just too small to be significant until you get closer to the speed of light, large distances are involved or you are talking about nuclear physics.

    I see QM as possibly the same way. There may be waves associated with objects in our everyday world but the wave is insignificant until the sizes are Planck scale and the energies are low.

    That doesn't clear up all of the "mysterious" nature of QM but it makes it less so and whether it's right or wrong (since that is unknown at the moment) it's an easier way to approach this subject for me.
     
  14. arfa brane call me arf Valued Senior Member

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    Entanglement can be measured, it can be distilled and purified. Mostly there is always an entropy of entanglement.

    There are lots of ways to define entanglement measures though.
    p.s. another name for an entangled state is a Bell state.
     
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  15. karenmansker HSIRI Banned

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    Well . . . . . THAT certainly rings a Bell . . . .HAHA!

    BTW: In Aspect's (and others) entanglement experiments, what were the distances involved (inches, feet, light years?). We are 'told' that entanglement operates over vast (light-year) distances - perhaps, if no intervening particle 'trip' interactions (see my previous post above). Were the experimental results actually detected directly (e.g., opposite states?) or were they mathematically/statistically inferred?
     
    Last edited: May 31, 2017
  16. danshawen Valued Senior Member

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    Our knowledge about quantum entanglement began with Pauli's exclusion principle.

    Within atomic structure, no two electrons in the electron cloud surrounding an atom may occupy the same energy state. A consequence of this is that pairs of electrons within atomic structure are entangled. One is in the quantum state termed "spin up", and its entangled twin is in the corresponding "spin down" quantum states. Electrons are fermions, which means, among other things, that they occupy half integer spin states within an atom.
     
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  17. danshawen Valued Senior Member

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    One of the really odd things about the way Maxwell put together his wave function for electromagnetic radiation is that the mechanism for producing photons is really not specified, other than to say that photons are produced when electrons are accelerated. Within atomic structure, this means the electron(s) that produced the photon (or absorbed a photon) transitioned from a higher to a lower, or from a lower to a higher energy state respectively.

    But to accelerate an electron ALWAYS requires another electric charge (or a photon, obviously). To PRODUCE a photon, either TWO electrons are needed, or in the special case of hydrogen, an electron and a proton.

    Why is this important to understand? Because to produce a photon entangled with itself, or to produce two entangled photons, two entangled electrons are required. Hence the WAVE FUNCTION of both the entangled electrons in atomic structure TOGETHER WITH the entangled photons(s) is really a single extended wave function, and this remains the case no matter how far the entangled photons may propagate.

    Any questions so far?
     
  18. karenmansker HSIRI Banned

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    Thanks, Nacho!:

    IMO, the slit portion (of the experimental design) is likely 'borderline' Planck scale since we are considering atoms (quantized) that comprise the slit material and that material's energetic edge interaction(s) with passing/interacting photons. The photon 'aspect' of the slit is more likely 'quantum' (possibly subquantum/subplanckian) until photon interaction with the slit occurs. IMO, 'diffraction' is due to interaction of the photon stream with the slit material, and as such is actually a 'special refraction condition' that involves exchange and transfer of energy between the photons and the slit edge material. Probably a similar condition exists for for electron (and other particle stream) 'diffraction'.

    IMO, my explanation for how slit diffraction occurs will 'raise the hackels' of many on this Forum. If you too want to risk such ire, I can send you a link if you will provide/PM your email to me.
     
  19. Seattle Valued Senior Member

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    What would "a photon entangled with itself" mean or look like?
     
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  20. Nacho Registered Senior Member

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    karenmansker,

    If I remember right, the experiment was performed on light, entangled by way of a cascade emission. I'm not sure of the exact distances -- I believe they were just a few meters -- but by timing constraints they were far enough apart that no signal could have traveled between the two detectors given the speed of light. There are some nuances of this experiment (Bell Inequality Tests) that I can't quite fathom, but they seem to mean that we have to accept FTL communications, and/or accept there are no hidden variables to the tests, or give up on realism (cause-effect, casualty). I'm at my limit here! and have probably stated some of that incorrectly.
     
  21. danshawen Valued Senior Member

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    It would have components of both left hand and right hand circular polarization; in other words, "unpolarized". Photons considered as wave energy have the property of superposition, so this is possible.
     
  22. Seattle Valued Senior Member

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    I think superposition is just a mathematical construct isn't it or it will turn out to be a more deterministic form of randomized (if that makes sense). I'm thinking of the pilot wave explanations or recent testing of oil droplets on a vibrating wave.

    In other words very random or erratic movement that "with perfect knowledge" would be deterministic as opposed to everywhere at once until measured.
     
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  23. danshawen Valued Senior Member

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    http://www.geneman.com/pubs/physics_bell/A_Physics_based_Disproof_of_Bells_Theorem.pdf

    Bell's Theorem has been falsified experimentally. He chose the wrong geometry.
     

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