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Micron sized object observed in quantum state

  1. Mar 18, 2010 #1
    In a following link:


    authors claim to design a 40 micron sized resonator which they were able to set into a superposition of states. Should this be true, I find it fascinating and a new, fruitful way to explore quantum-classical border. Any opinions or comments?
  2. jcsd
  3. Mar 18, 2010 #2
    cool, but there is no surprise and because "quantum-classical border" does not exist
  4. Mar 18, 2010 #3
    God, I really don't want to initiate another ("Local realism ruled out? (was: Photon entanglement and...) ") zillion posts thread, but how the hell do you think that there is no border? Because things around look mighty non-unitary to me ... :rolleyes:
  5. Mar 18, 2010 #4
    Do you think that systems with N atoms can be in superposition while systems with N+1 atoms cant? There are no people who seriously defend collapse interpretations after the discovery of Quantum Decoherence and (partial) resoltion of the measurement problem.

    If we exclude Mascoscopic realism aka Shut up and calculate interpretation, and with Collapse ruled out, there are only non-collapse interpretations left, so the is no any "border". Any system can be put in superposition: atom, C60 molecule or a cat
  6. Mar 18, 2010 #5
    Well said, and in my opinion that's the view of many people actually working in the field. I don't really understand why people are so obsessed with formulating Interpretations for an incomplete (albiet AMAZING and fruitful) theory? QM is an amazing collection of principles, but so many of the problems it creates exist only in the minds of theoreticians and such, and are simply resolved incrementally as we are able to observe new phenomena, or old ones with new methods (and higher energy levels).

    We're at a point where people are honestly debating whether a kind of... elongated... dipole in a spin-ice is a magnetic monopole in "The Dirac Sea". Everything has to be formulated now in terms of an ultimate theory, when the reality IS incremental steps with tipping points. We can't CHOOSE our tipping points...
  7. Mar 18, 2010 #6


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    It is not actually very surprising that they've succeded. People have been working on exactly this type of experiment for a few years now (I've actually been involved in one such project myself) and there are several papers where people have managed to cool a MEMS resonator into a very low state. There are at least a couple of other groups that are likely to manage to repeat the same experiment later this year, Cleland and co just happened to be faster than anyone else.
    So yes, it is certainly true. The physics is also quite well understood since people have been doing exactly the same type of experiement with qubits and electromagnetic resonators for a few years (since 2004). It would have been more suprising if it had NOT worked with a good MEMS resonator.

    So yes, it is a very impressive experiment and a nice demonstration of QM; but the result is not surprising to me or anyone else that knows something about the field, and I am not sure it really tells us something new about QM.
    Last edited by a moderator: Apr 24, 2017
  8. Mar 18, 2010 #7
    True, but every Apollo mission needs its predecessors.
  9. Mar 19, 2010 #8
    Yeah, there are serious lack of diffuse boundaries in physics. :biggrin: You are aware you just pulled classical sophism on me as an argument?

    Ok, I looked it up and you seem to know what you are talking about and others seem to support you. So, IIUC When interacting with environment, state of isolated system get's "lost" by a unitary developement in larger phase space. Due to a much larger number of dimensions, part of new phase space that state is lost in can usually be projected to only one eignestate of original isolated system thus giving appearance of collapse - did I get that right?

    Because there is only unitary development and correlation don't end - thay basically quickly become so "fine" that we can no longer practically difference them from any alike correlation thus giving us random view.

    This is really interesting. I am far from convinced, but interested.

    And no offence but ... I will not take your work for that cat. :)
  10. Mar 19, 2010 #9
    Cool experiment, but it would only get really interesting if they managed to make the metal strip interfere with itself. I'm talking about something analogous to the double-slit experiment. Now that would be something.
  11. Mar 19, 2010 #10
    What exactly is interesing?
    Do you still believe in Copenhagen Interpretation and Collapse? Then you are probably the last one on this forum :)
  12. Mar 20, 2010 #11
    right, quantum mechanics is demonstrated, like say you; unsurprising, foreseeable, expected.
    but what is really at stake, is, the standard quantum mechanics vs nonlinear quantum mechanics, not the superposition itself (per se), but the time of the superposition vs the time of decoherence, if last more or less; if last less, nonlinear model are the correct, if last more, linear models are.
    from various sources there is growing evidence for nonlinear models (specific tests must be developed for them, to see which one is the correct).
    Last edited: Mar 20, 2010
  13. Mar 21, 2010 #12
    ah, you look at it as a test of objective collapse theories?
  14. Mar 21, 2010 #13

    Decoherence is a collapse. A natural collapse of many systems.
  15. Mar 21, 2010 #14
    No, decoherence is vanishing of the non-diagonal elements.
    Collapse is more: only one element (one branch) is left.
    Last edited: Mar 21, 2010
  16. Mar 21, 2010 #15
    Correct me if i am wrong, but decoherence is when particles systems fall into quantum mechanically-defined states. This is still found by their constituent wave functions to be a probability yes of [itex]\int |\psi|^2[/itex]?

    Perhaps wiki is more your street?

    ''Quantum decoherence gives the appearance of wave function collapse''

  17. Mar 21, 2010 #16
    From the same article:

    So decoherence explains why we don't see superposition of dead and alive cat, but it does not explain why nature cohses the specific state of a cat. For me, as I like MWI, both cats exist.
  18. Mar 21, 2010 #17
    I've never seen a problem with this. The ''why'' seems quite obvious; the more a particles wave function entangles with a system of other quantum entangled objects, the more probability of a wave function-like appearance of a collapse. It's like a natural cut-off for frequencies in their wave functions.
  19. Mar 21, 2010 #18
    Yes, as a result of decoherence superposition collapses into:

    sad observer looking at dad cat
    happy observer looking at alive cat

    so cat is dead AND alive, but it does not explain why cat is dead OR alive
    In another words, QM without collapse (with decoherence) is deterministic, so if it is deterministic, why the world looks random for us? There are different ways to explain this: MWI, BM for example
  20. Mar 21, 2010 #19
    Both states cannot exist. One must exist in more a defined state than the other. Macroevents do not exist as states [itex]|\psi>=\frac{1}{2}A|\psi>+\frac{1}{2}B|\psi>[/itex] - macroevents are not in a high wave function state like quantum particles. It has a vanishingly small wavefunction in fact. You will by quantum mechanical laws of decoherence, find either the cat dead or alive, but never both.
  21. Mar 21, 2010 #20
    No, they DO exist. If you have 2 outcomes with the same probability, then in deterministic theory (and QM with decoherence withoutcollapse is the one) you can not in principle explain why only one specific outcome exist. Why, for example, that specific neutron decayed at 745th second, while another one at 739th?

    And yes, macroevents can't coexist - in one branch but they can coexist in different branches! so yes, it is "vanishingly small" possibility to observe another branch. Different branches simple stop interacting.
  22. Mar 21, 2010 #21
    Another example: I have 2 neutrons: Left and Right. Setup is symmetric
    I wait which neutron decays first. Say, L decayed first. Now P symmetry is broken.

    Do you understand that deterministic theory can't, in principle, break P symmetry?
  23. Mar 21, 2010 #22

    The last post was specifically aimed at your macro-environmental approach - nothing to do with quantum objects. You can't have the experiment say two cats are dead and alive when their is a cutoff in the wave function for them.
  24. Mar 21, 2010 #23
    Yes, and this is the whole point of the decoherence: it explains why it is true.

    But decoherence (check again wiki article) itselft does not explain how deterministic evolution of global wavefunction of the universe appears 'random' to the observers. It just explains why observers dont see a superposition of outcomes, but it does not explain how particular outcome is chosen.
  25. Mar 21, 2010 #24
    Observers do not have many explanations in physics, from were we stand. Our lack of knowledge in a system makes the universe appear so ''randomly-chosen''. Deterministic physics will always question how and why the great blue-print manifested.
  26. Mar 21, 2010 #25
    We don't know what the "consciousness" is, but we still can talk about the dead observers in terms of the state of their memory. For example, a question how photo-camera + computer behaves is a valid physical question which does not include consiousness.

    Non-collapse interpretations, like MWI and BM are motivated by the fact that decoherence does not explain that apparent randomness.
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