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Weak measurements? Modified Double slit

  1. Jul 25, 2007 #1
    I came upon a very interesting article today:
    http://www.msnbc.msn.com/id/19875410/site/newsweek/

    I wanted to confirm what I read... this is the first time I ever heard of this kind of thing, and I was wondering if any of you have seen this before.

    It talks about a tweak of Young's double slit experiment. This is the main part.
    "If the blinds are closed so the detectors cannot see the slits, photons fly through both and form the stripes. Here's the twist: if the blinds open only after photons have passed the slits but before they reach the blinds, the stripes fail to form even though the photons have seemingly done what they must to form stripes—namely, fly through two slits, as they always do when unobserved. The act of observing alters what the photons did earlier, somehow changing things so they passed through one slit and not two."
     
  2. jcsd
  3. Jul 25, 2007 #2
    Could somebody knowing about experiments confirm if it is possible to measure which slit a photon went through? I understood it is possible for electrons, but is it also for photons? How?
     
  4. Jul 25, 2007 #3
    The “father” of that stuff is Y.Aharonov; see for example Y. Aharonov and L.Vaidman, Phys.Rev.A, 41, 11, (1990) and refs in it (as early as 1987). I never listen of any experimental confirmation and personally consider the paper wrong. However, there is remarkable footnote in it (#7) which is wrong mathematically (beta is not necessary real) but very deep physically (Yakir Aharonov outcome!).

    Regards, Dany.
     
  5. Jul 25, 2007 #4

    The paraphrasing of the 'experiment' in the article throws things off for me reading it, but my first thought is: it's amazing they are that good (and quick) at opening/closing the 'blinds'.---
     
    Last edited: Jul 25, 2007
  6. Jul 25, 2007 #5
    Come on! You need a journalist to make your mind about scientific paper?

    Regards, Dany.
     
  7. Jul 25, 2007 #6
    I was saying (in a 'weaker than my usual' self)--that it didn't sound right and how in the world (->amazing!!!*) can they block part off (the blinds) anything while a photon (wave?) is in flight (or whatever)/(as the article paraphrases it).--it sounds like another (-t) experiment.
     
    Last edited: Jul 25, 2007
  8. Jul 25, 2007 #7
    It will be interesting to read your arguments after you will be familiar with the arguments of Y.Aharonov/L. Vaidman/A. Casher/D. Albert (believe me, they are world league).

    Regards, Dany.
     
  9. Jul 25, 2007 #8

    I see they have many papers:


    http://eprintweb.org/S/authors/All/va/Vaidman

    http://eprintweb.org/S/authors/All/ah/Y_Aharonov


    there's just a (deep) personal feeling about all the entanglement/non-local/(-t) which doesn't settle any of the ambiguities with my view of quantum. It's a developing viewpoint which---............(hmmm)---




    ----let's go a different direction:


    why did you write?:

    "I never listen of any experimental confirmation and personally consider the paper wrong. However, there is remarkable footnote in it (#7) which is wrong mathematically (beta is not necessary real) but very deep physically..."
     
  10. Jul 25, 2007 #9

    Cthugha

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    That is no problem. The easiest way is to use linearly polarized light and put quarter wave plates immediately behind the slits. One plate makes the light become left handed circular polarized. The other makes it become right handed circular polarized.
    So you can tell which slit a photon went through by looking at its polarization. Some quantum eraser experiments work this way.
     
  11. Jul 25, 2007 #10
    I never listen of any experimental confirmation - just fact, but may be I missed something.

    personally consider the paper wrong – I wrote paper (quant-ph/0606121) which contradicts it. However, Y. Aharonov, A. Casher and S. Nussinov came independently to the same conclusion as far as the connection between L. Carroll and E. Schrödinger fantasies is considered. The entertainment detail is that Leva said that he consider my paper wrong. I asked him why. And he answered that he is not familiar with the math of Hilbert spaces (but like my relativity statements). He asks me not to recommend him as a referee.

    there is remarkable footnote in it (#7) which is wrong mathematically (beta is not necessary real) but very deep physically – I recently finished investigation which is further generalization of that point and allow to consider “relative states” locally.

    Regards, Dany.
     
  12. Jul 25, 2007 #11
    What I don't understand in this description is why this should be a surprise: if I open the venetian blinds, how should I get an interference pattern on the blinds. This does not need quantum theory. If the light falls through the blinds, certainly there is no interference on the blinds. What am I missing?

    Harald.
     
  13. Jul 25, 2007 #12
    nice paper---I like classical approaches too. Did you write the paper after/because of the one noted in the newsweek article? --and have you got a copy of your new paper available? I, again, also, like the idea of local "relative states" --although we may approach them (and specifically) in a different way.

    ----------------------------------------------------

    I wonder if anyone has written a paper from an idea that initiated here on the PF?
     
    Last edited: Jul 25, 2007
  14. Jul 25, 2007 #13
    Given the paper number (quant-ph/0606121), how can i view it? Sorry, im new to this
     
  15. Jul 25, 2007 #14

    George Jones

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    The arXiv is here. Under Physics, click on Quatum Physics (on the left of the page); this should take you here.

    The first 06 means 2006, so click on 2006. Once you're in 2006, click on 0606 (2006, June). Finally, find article number 121 in 0606.
     
  16. Jul 26, 2007 #15
    George Jones, thank you. Even simpler in one step: type the paper number under Search or Article-id and click.

    Regards, Dany.
     
  17. Jul 26, 2007 #16
    There are "many histories" a photon could have, such as passing through one slit or two, Davies writes in his new book, "Cosmic Jackpot."” – I have no idea who is Paul Davies and certainly do not intent to read his book. I consider all “interpretations” without exception nonsense. I am not familiar with the classical theory which required interpretation.

    However, if you mean Y. Aharonov and L.Vaidman, Phys.Rev.A, 41, 11, (1990): then no/yes.

    No: The identification of the classical physics with the set of real Hilbert spaces was the result obtained in my Ph.D. study. The approach was strongly supported by L.P. Horwitz, Y. Aharonov and N. Rosen. When I had been involved into Quantum Information and Quantum Communication stuff it was clear for me that the central problem is the communication between the quantum computer and the readers/writers. It was obvious that the languages should be matched.

    Yes: The solution was just in front of my eyes but somehow I did not see it. I do not remember why I looked at Yakir paper (I usually do that to know what he is doing). I started read the paper and met the footnote. I was shocked. I realized that I see something very important. Several hours I looked on two lines and finally the coin collapsed: it explains why the wave packet spread (notice that exp (i*phi) =cos (phi) +i*sin (phi) – the wave packet with the exactly the same structure).

    The rest was practically instant.

    No, I did not write it yet. Notice that the mistake in footnote mentioned above is the relative phase. Now if you apply the same operator to |psi1> together you will get the Hadamard matrix and the Zeilinger “eigenschaften”. It works in general. That is the idea (the content).

    I don’t know about anyone else, but that one is connected with my discussions with CarlB and DrChinese. Another one in progress about the coherent states is connected with my discussions mainly with Vanesch and most important for me uses the idea (explanations) provided for me by Hans de Vries. It isn’t finished yet but related to my already published paper that may be interesting for you: physics/0504008.

    By the way, in the session where Hans de Vries did that it was somebody that called his explanations “garbage”. I could not hold myself cool and called him “idiot”.

    I believe that your idea is also something. Now I understand why ZapperZ did not answer. If you understand something in the details of particle accelerators, go ahead.

    Raffiniert ist der Herr Gott, aber boshaft ist er nicht.

    Regards, Dany.
     
    Last edited: Jul 26, 2007
  18. Jul 26, 2007 #17
    my, my, my---let's see.....

    I consider all “interpretations” without exception nonsense. I am not familiar with the classical theory which required interpretation.

    I get the feeling you're thinking of something specific here (maybe, CI ?). My idea of 'interpretation' is that it follows some of the analogies in the story of the house build on sand.



    I read "Measurement of the Schrodinger wave of a single particle"

    http://xxx.lanl.gov/abs/hep-th/9304147

    "This is our main argument for associating physical reality with the quantum state of a single particle."

    and

    "If we are interested in all the details of this
    time-dependent state we cannot use measurements which are too slow. Every measurement
    of the density and current of a Schrodinger wave must last a period of
    time which is smaller then the characteristic time of the evolution of the state; and
    the time intervals between consecutive protections must be even smaller. However,
    in principle, Schrodinger wave measurement to any desired accuracy is possible:
    for any desired accuracy there is a density of the state-verification measurements
    that will protect the state from being changed due to the measurement interaction."

    and

    "Our direct measurements
    of the density and the current of the Schrodinger wave challenge the
    commonly accepted notion that quantum states can be observed fully only when
    the measurement is performed on an ensemble of identical systems."

    and can see that you admire his (Aharonov's) work---do you know him personally? (you referred to him as 'Yakir', like he may be an acquaintance)

    Y. Aharonov and L.Vaidman, Phys.Rev.A, 41, 11, (1990)

    Resolution of a “Retrodiction Paradox” ?---is this the paper you mean?


    It isn’t finished yet but related to my already published paper that may be interesting for you: physics/0504008.

    yes--I read that at the same time as your other one---and I can see a 'little' correlation to the interest in accelerators.

    and (I am grateful to L.P. Horwitz, Y. Aharonov, S. Nussinov, and I.D. Vagner
    for the stimulating discussions.)---Was this a 'local' thing/conversation?---yes, I was looking for 'something' in that thread and... ---oh well)


    Raffiniert ist der Herr Gott, aber boshaft ist er nicht.

    Something specific?---or did you go to Princeton?


    It is amazing to me how little lab work he did--(or, at least, how it is written about his 'distain for'/'absence of' it)

    ---------------------
    The rest was practically instant.

    Isn't that one of the greatest feelings when it happens--and it doesn't seem to happen often enough.
     
    Last edited: Jul 26, 2007
  19. Jul 26, 2007 #18
    No. The paper entitled “Properties of a quantum system during the time interval between two measurements”.

    This is well known aphorism of A. Einstein that means:

    God is subtle, but he is not malicious.

    Go to Princeton? Unfortunately, it is too late. Today is 2007.

    Regards, Dany.
     
  20. Jul 26, 2007 #19
    No. The paper entitled “Properties of a quantum system during the time interval between two measurements”.

    OK--I'll take a look


    This is well known aphorism of A. Einstein that means:

    God is subtle, but he is not malicious.

    Go to Princeton? Unfortunately, it is too late. Today is 2007.


    I was wondering it you were applying to some part of your thread. (it's above some door at Princeton--I thought you may have went there)

    Do you know Aharonov personally? (you referred to him as 'Yakir', like he may be an acquaintance)
     
  21. Jul 26, 2007 #20


    I think we moved too far from OP. The only real contribution was made by George Jones, that is, the demonstration how Mephisto may find the relevant information using names, paper ID, etc. We added some colour to it.

    In order to finish that discussion in proper mood, I will tell you that your question is connected with the great mystery in my life. I never visited Princeton; long ago S.L. Adler sent me invitation to give seminar there. I received the letter two years later after it was sent. Would you believe? I mean about 10 days or never. But after two years!

    Regards, Dany.
     
    Last edited: Jul 26, 2007
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