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Re-preparing a dust particle

  1. Feb 5, 2016 #1
    A few photons (even 2?) are enough to decoherence a dust particle in space (position eigenstates chosen) . If further photons impinge on it.. Can the dust particle be re-prepared? I think yes because the quantum is never switched of. So that it mean whenever eigenstates were chosen via decoherence.. it can still be reprepared, is this correct?

    If so.. then it is technically possible to re-prepare a small stone to change shape by shining massive laser photons into it? How? What must be the experimental setup to do that? And why not? What experiments have this done akin to this?
     
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  3. Feb 5, 2016 #2

    bhobba

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    Only in very simple cases can decoherence be undone.

    Thanks
    Bill
     
  4. Feb 5, 2016 #3
    You mean to say when decoherence occurs and eigenstates chosen.. any additional photons would no longer re-prepare it? And the only way it can be re-prepare is to initiate re-coherence?

    But Zurek argument for Einselection is the system can be reprepared by interacting with it.. that's why he proposed propagating states to the environment in quantum Darwinism. How do you reconcile this with what you mention a quantum system needs recoherence first before further photons can re-prepare it?
     
  5. Feb 5, 2016 #4

    bhobba

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    I am saying decoherence has scrambled it so much nothing you can do can unscramble it.

    Thanks
    Bill
     
  6. Feb 5, 2016 #5
    So why is Zurek worried about the observers repreparing the system. Or better a quote: http://arxiv.org/pdf/0903.5082v1.pdf


    "Fragility of states is the second problem with quantumclassical
    correspondence: Upon measurement, a general
    preexisting quantum state is erased { it \collapses" into
    an eigenstate of the measured observable. How is it then
    possible that objects we deal with can be safely observed,
    even though their basic building blocks are quantum?"
     
  7. Feb 5, 2016 #6

    bhobba

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    Beats me. Phases usually get very scrambled so much so you cant restore it. In principle it can be - in practice it can't - except as I said in simple cases eg the quantum eraser. This is very very well known, so I think you need to carefully understand Zurek's context.

    Added Later:
    That's Zurek's quantum Darwinism paper. I know a bit about it but am no expert on it. What Zueck is attemptiong to do though is develop observations as stable manifestations of decoherence. I supect its related to that stability criteria.

    Schlosshauer examines this in his standard text:
    https://www.amazon.com/Decoherence-Classical-Transition-Frontiers-Collection/dp/3540357734

    The general requirement is the basis that emerges must commute with the Hamiltonian or something like that to be stable.

    Thanks
    Bill
     
    Last edited by a moderator: May 7, 2017
  8. Feb 5, 2016 #7
    I see. So I guess he meant only for simple quantum system.. not complex one..

    Speaking of complex system. If you have decoherence without born rule selection (or no eigenstates chosen), the phases are still so scrambled that you can see the object in one location.. and since the eigenstates were in the order of 0.0000001 micron distance.. we won't able to tell whether it has any eigenstates chosen.. so without born rule selected.. won't you be able to see it having classical positions?
     
  9. Feb 5, 2016 #8

    bhobba

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    I am not sure I understand your question. However it is of some controversy if Zurek's derivation of the Born rule is correct - many think its circular.

    BTW I looked up in Schlosshauer where he discusses it. Its on page 73. I personally find him easier to understand that Zurek who I find wordy and somewhat obscure because of it.

    Thanks
    Bill
     
  10. Feb 5, 2016 #9
    Isn't it decoherence and born rule are separate.. if classical objects like table just has decoherence but no born rule selected (no position eigenstates selected).. what would you see.. would you still see a table? (just for sake of discussion)
     
  11. Feb 5, 2016 #10

    bhobba

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    Zurek tries to derive it from decoherence via a process called envarience:
    http://arxiv.org/abs/quant-ph/0405161

    Its rather controversial.

    I personally am ambivalent to it and prefer Gleason.

    We are however straying way off topic. If you want to pursue it best to start another thread.

    Thanks
    Bill
     
  12. Feb 6, 2016 #11
    According to http://www.univie.ac.at/qfp/research/matterwave/decoherence/index.html
    "According to decoherence theory a typical collision with a gas particle localizes the fullerene to the scale of about 1 nm,"

    Bill. In the above where the fullerene interacts with hot gas particle on way to detector, does the born rule already apply or does it mean an eigenstate is chosen? Or can localization occur without any born rule applied (note the above mention "localizes")?
     
  13. Feb 6, 2016 #12

    bhobba

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    I have zero idea what you mean by that. The Born rule is an integral part of QM. Zurek claims you can derive it from the state and a symmetry of etanglement - so its there regardless.

    Thanks
    Bill
     
    Last edited: Feb 6, 2016
  14. Feb 6, 2016 #13
    Born rule is related to collapse. I was asking if the Fullerene hitting the gas particle can collapse it (or eigenstates formed) before reaching the detector? If not.. I was wondering why only the screen detector can make the Fullerene form eigenstates (or collapse or many worlds branches established or Ensemble statistics engaged or whatever you want to name collapse)?
     
  15. Feb 6, 2016 #14

    bhobba

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    Not necessarily. Its related to observation. Collapse may or may not occur. If Zueck is correct you cant have QM without the Born rule - it makes no sense.

    Here is the Born Rule;
    There exists a positive operator of unit trace, P, such that given an observable O, the expectation of the outcome is Trace(PO).

    Zurek thinks the existence of a wave-function and entanglement leads to the Born rule. That means your question makes no sense - at least I cant see any in it.

    If you want to pursue it I will have to leave it to someone else.

    Thanks
    Bill
     
    Last edited: Feb 6, 2016
  16. Feb 6, 2016 #15

    bhobba

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    I would say yes - but I cant recall seeing a model of that situation.

    Thanks
    Bill
     
  17. Feb 6, 2016 #16
    You mentioned born rule is related to observation (let's ignore Zurek for now but the mainstream view). So if we don't "observe" the fullerume hitting the gas particle.. it looked like collapse has occur but because we don't use observation, then we can't use born rule. Is this what you mean (at least believed by the mainstream)?
     
  18. Feb 6, 2016 #17

    bhobba

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    Decoherence converts a superposition to a mixed state. The modern view is to consider it a proper mixed state so observation effectively has occurred.

    Thanks
    Bill
     
  19. Feb 6, 2016 #18
    You keep saying this. The Ensemble view is like someone asking how a television screen work.. and giving the answer.. "the modern view is to consider it as proper display so observation effectively has occurred".. this is because of ignorance of the internal circuitry of a television. One billion years from now. when the quantum mystery is solved (that may require beyond quantum gravity).. this analogy may be accurate.. isn't it.
     
  20. Feb 6, 2016 #19

    bhobba

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    You are making unwarranted assumptions on assumptions. It may be that nature is simply like that.

    Many people have not thought about the nature of explanation and every explanation requires assumptions. You have gained nothing in a fundamental sense explaining one thing by another. QM is one area confusion abounds unless you take that on board.

    Thanks
    Bill
     
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