Handle with care

In today’s quant-ph we find a report of a truly dramatic experiment — one that detected entanglement between Baton Rouge, Louisiana and Givarlais, France. How, you ask: by fiber-optic cable? Satellite? Neither: by postal mail! The authors don’t say if it was FedEx, UPS, or some other carrier that managed to ship half an EPR pair across the Atlantic without decohering it — but whoever it was, that’s who I’m using from now on.

(Note: On close reading, it appears that when the authors use the word “entanglement,” they actually mean “classical correlation.” However, this is a technical distinction that should only matter for experts.)

31 Responses to “Handle with care”

  1. Robin Blume-Kohout Says:

    Er, as the script kiddies say, “WTF”?

    Just as a sort of footnote to your footnote, “entanglement” appears to mean not just any old classical correlation, but the instantaneous communication kind. At least that’s what a cursory reading seems to indicate. Are the words “sympathetic magic” appropriate here, or did I miss something?

  2. Anonymous Says:

    Did you mean to link to http://www.arxiv.org/list/quant-ph/new, rather than a specific article appearing in the retrieval?

  3. Scott Says:

    Did you mean to link to http://www.arxiv.org/list/quant-ph/new, rather than a specific article appearing in the retrieval?

    No.

  4. Anonymous Says:

    So they were able to detect through some kind of response to heating in one crystal whether the other crystal had been heated or not? Doesn’t that violate the “no useable super-lightspeed information” rule (if the crystals can be brought far enough apart and have the experiment still work)?

    This probably just means I’ve misunderstood something fundamental, but what?

  5. Scott Says:

    This probably just means I’ve misunderstood something fundamental, but what?

    That the paper is completely wrong! If the authors mean instantaneous communication, then what they’re reporting is impossible; if (let’s give them the benefit of the doubt) they instead mean classical correlation, then what they’re reporting is trivial. There’s no indication anywhere that the authors understand what it means to test (for example) for a Bell inequality violation, let alone maintain an EPR pair for several months with the two halves on different continents (!).

    Help me, readers! What should I do? Should I just stop being sarcastic? Should I insert little “wink, winks”?

  6. Dave Bacon Says:

    I for one will just assume from now on that everything you say, Scott, is sarcastic. Then you will need to invent some little symbol for when you are being serious.

  7. Scott Says:

    <serious>Good idea, Dave!</serious>

  8. Anonymous Says:

    Their document doesn’t even pass the well-known “Microsoft Word” test for validity.

  9. Anonymous Says:

    <sa:semi-serious>Maybe this can be added to the W3C’s standardization agenda.</sa:semi-serious>

    [Why is it, whenever I see someone named Dave addressed by name in an email or blog comment, I hear echoes of "I'm sorry Dave, I'm afraid I can't do that." More here...]

  10. Anonymous Says:

    <serious>Good idea, Dave!</serious>

    are you being serious scott? ;)

  11. Scott Says:

    <serious><serious>Of course I am.</serious></serious>

  12. William Says:

    If they kept the wavefunction uncollapsed, they must not have observed the address on the package before shipping. So it was probably UPS.

  13. Anonymous Says:


    Help me, readers! What should I do? Should I just stop being sarcastic? Should I insert little “wink, winks”?

    Scott, it’s simple. You just have to resist the temptation to say when you’re being sarcastic and take delight in the (inevitable) argument about whether or not your post was sarcastic in the comments.

  14. quant-ph Says:

    Where’s the link to the referenced paper? Parent post links only to quant-ph/new/.

  15. Scott Says:

    Oops — so that’s what anonymous 10:25 was trying to tell me before! I assumed that I had linked to the article, and that this commenter was telling me I should instead link to quant-ph/new for some stupid and inexplicable reason. Sorry, my bad! It’s fixed now.

  16. Anonymous Says:

    This has nothing to do with anything:

    http://www.msnbc.msn.com/id/15321167/

  17. Anonymous Says:

    Speaking of entanglement, care to comment on this gobbledegook that’s making the rounds?

    http://seattlepi.nwsource.com/local/292378_timeguy15.html

  18. John Sidles Says:

    Anonymous said … Speaking of entanglement, care to comment on this gobbledegook that’s making the rounds?

    That reference is to an experiment being run at the University of Washington by John Cramer and Warren Nagourney, whose goal is to look for backwards causality in quantum measurements.

    I know both physicists quite well, and in particular, have discussed the physics of the experiment at some length with John.

    The quick summary is this: John understands perfectly well that if the orthodox POVM-based description of quantum measurement is true, then no backwards causality will be observed.

    Being himself an ultra-orthodox experimentalist, Cramer is strongly motivated to test the logical obverse, which is of course, that if backwards causality is observed, then POVM quantum mechanics is not true.

    It was on partly on this basis that his and Warren’s proposal passed peer-review; it also helped that the experiment itself is well-designed, and Warren is well qualified to run it.

    Which leads us to ask, is it even conceivable that POVM-based quantum mechanics (the foundation of e.g. “Mike and Ike”) is not true?

    Well, there are at least two plausible mechanisms: one is that measurement processes are described by physics outside of QM (like Cramer’s own transactional theories of measurement), the other (related) is that the dimensionality of Hilbert Space, viewed as a physical resource, is simply not big enough to describe classical observers via POVM-type mechanisms, because these mechanisms are too profligate of dimensionality.

    Just to challenge the POVM-loving theorists of Shtetl Optimized with a Fermi Question: how large does the dimensionality of Hilbert Space have to be, to describe a POVM universe large enough to host the Shtetl Optimized blog? And how can this number be measured?

    This pure number is seemingly an important physical constant of the universe. Therefore, a central question for POVM orthodoxy is, why is this physical constant so large? Obviously this question is directly tied to major mysteries of quantum field theory and quantum gravity, namely, the ubiquity of ultraviolet and infrared divergences.

    It is very remarkable IMHO that this important physical constant is not discussed, or even given a name, in any QM textbook that I know of.

    These considerations illustrate a duality which IMHO is essential to the vigor of physics: orthodox theorists and orthodox experimentalists each regard the other as heterodox!

    Just to state my own point of view—which is that of most engineers—I whole-heartedly embrace POVM quantum orthodoxy. And so, I am confident that the Cramer/Nagourney experiment will not see a causality-violating signal.

    Which leaves me marveling that Hilbert Space is so big.

    ——-

    As for making fun of the Cramer/Nagourney experiment: “Derision is pleasure arising from our conceiving the presence of a quality, which we despise, in an object which we hate. … Between derision (which I have stated to be bad) and laughter I recognize a great difference. (Spinoza)”

  19. chris Says:

    Which leaves me marveling that Hilbert Space is so big.

    Do you marvel similarly at the size of , say, the 1000th Busy Beaver number? And if not, why not?

  20. Niel Says:

    Just to challenge the POVM-loving theorists of Shtetl Optimized with a Fermi Question: how large does the dimensionality of Hilbert Space have to be, to describe a POVM universe large enough to host the Shtetl Optimized blog? And how can this number be measured?

    This pure number is seemingly an important physical constant of the universe. Therefore, a central question for POVM orthodoxy is, why is this physical constant so large?

    Wow! I wasn’t aware that the doings of Shtetl-Optimised and it’s readership were to important to the goings on of the universe.

    It seems to me that this question is related to the amount of energy in the universe and the number of particles in the universe, which (even without QM) are in principle similarly awe-inspiring, large, and unmeasurable “pure numbers”. Should we contemplate the threshold energy below which a universe which supports us is impossible?

  21. John Sidles Says:

    Just to remark, the question “Why is the dimensionality of Hilbert Space so big?” is equivalent to the seemingly unrelated question “Why is quantum measurement random?”

    The following simple argument explains why.

    Suppose that an experiment involving interferometric measurement has 2^n possible outcomes, where n is the number of photons that pass through an interferometric beamsplitter to be detected by either of a pair of diodes. Here n~10^16 would be a typical number of detected photons in a real-world experiment.

    Then according to Chaitin’s Theorem, all but an exponentially small fraction of possible experimental records (the n-bit long record of which photodetector fired on the i‘th detected photon) will not be algorithmically compressible.

    Since algorithmic incompressibility is the definition of “random”, it follows that large-dimension Hilbert spaces must predict random experimental results. QED!

    This simple argument is well-known within the quantum measurement community (I discussed in with Chaitin years afgo), but I have never seen it in a QM textbook!

    The point being, that the large dimensionality of quantum Hilbert space is indeed one of the deepest mysteries of physics.

  22. Anonymous Says:

    This discussion is absolutely amazing but I don’t understand a word of it. What do I do?

  23. Anonymous Says:

    J.Sidles writes: “The point being, that the large dimensionality of quantum Hilbert space is indeed one of the deepest mysteries of physics.”

    Well, it seems that J. von Meumann wrote to G.D. Birkhoff, on 13 November 1935 (the EPR year!), “I would like to make a confession which may seem immoral: I do not believe in Hilbert Space anymore.”
    (G.D. Birkhoff, Proceedings of Symposia in Pure Mathematics, Vol. 2, p. 158, ed. R.P. Dilworth, American Math. Soc., Rhode Island, 1961).
    It seems to me that even the concept of “state” (and the term itself) is a bit tricky in a science based on measurements of observables that have no values before the measurements! See, ie, the second of the ‘Ten commandments of the church of the smaller Hilbert Space’ by M.Leifer.

  24. John Sidles Says:

    Thanks, anonymous. Here is a link to Liefer’s (very humorous) quantum commandments, which I enjoyed very much.

    May I say, anonymous, that you’ve written upon a remarkably broad range of topics :)

  25. scerir Says:

    Thanks John.
    No, unfortunately I’m not ‘that’ anonymous. I’m a photographer [1], and QM is just a little hobby.
    Regards,
    -serafino
    [1] I also took a picture of a Schroedinger cat, at home, before he self-collapsed away.
    http://www.flickr.com/photos/scerir/61885189/in/set-1297721/

  26. ichabod Says:

    Hey Scott, why would you post this? Why not just email the authors pointing out their misunderstanding — what is the point in publicly ridiculing them? I have seen you do this many times, and I wonder why a smart guy needs to bully others. And also why point out a mistake which will have little impact, and which is not a challenge
    to debunk.

    You can advance understanding without kicking other people in the face, just because they missed something you didn’t. All this does is discourage people from going into science. Many just can’t be bothered to put up with the pervasive intellectural-bullying which can exist in some fields.

    I admire people who are smart without feeling the need to prove they are smarter than others.

  27. Scott Says:

    Why not just email the authors pointing out their misunderstanding — what is the point in publicly ridiculing them?

    ichabod, I actually sympathize with your viewpoint — it’s the one I held 5 or 6 years ago. But have you ever tried emailing someone to point out a misunderstanding of this magnitude? Spending hours, days, or weeks boxing shadows, weaving sand, nailing Jello to a wall? After you’ve done it a few dozen times, it really changes your perspective.

    Since the arXiv isn’t peer-reviewed, the only way to impose a penalty for posting this sort of thing is through vigilante blog-justice. I try not to be as nasty as (say) Borat, or some of the anonymous commenters on this blog.

    But since it ’tis the season for mercy and compassion, let me make a standing offer to anyone whose errors I’ve ridiculed here: repent, and all will be publicly forgiven.

  28. John Sidles Says:

    I like Scott’s and Dave Bacon’s blogs because they so often communicate, not derision, but rather shared enthusiasm, which word—if I remember correctly—derives from the greek enthousiamos (sp?) meaning: possession by a god, supernatural inspiration, prophetic or poetic frenzy; … an occasion or manifestation of these.

    Speaking of which, I have just learned that there are deep mathematical connections between Kahler manifolds being ruled (which is important to engineers for achieving high numerical efficiency), and their having constant scalar Ricci curvature (which is important for achieving high fidelity in quantum MOR calculations).

    Here “deep mathematical connections” means, Iunderstandnotoneword.

    What else can we expect, when the gods speak to mortal humanzees? :)

  29. Anonymous Says:

    “This discussion is absolutely amazing but I don’t understand a word of it. What do I do?”

    for starters, go here:

    http://math.ucr.edu/home/baez/books.html

  30. John Sidles Says:

    Anonymous recommends: [John Baez' reading list How to Learn Math and Physics]

    … which is a truly wonderful reading list!

    And yet … by omission, Baez’ list suggests that that carbon-based, recently-evolved, primate-derived life forms can do math and physics perfectly well, without even knowing that they are carbon-based, recently-evolved, and primate-derived!

    Also, the whole point of Baez’ reading list to teach students how to generate new ideas … and yet the list omits any formal study of the history of ideas. Very interesting!

    On a less-stressed planet, or in an earlier century, it might have been OK to “drop these classes”. But surely, this is not that planet, or that century?

    Of course, there are other, more intellectually challenging reading lists out there. :)

    ———-

    BURKE: Look, this is a multimillion dollar operation. He can’t make that kind of decision. He’s just a grunt!

    … (glances at Hicks) No offense.

    HICKS: (coolly) None taken.

    ———-

  31. Anonymous Says:

    I think it is a good idea to post trackback to arxiv articles that get mentioned in blogs, especially in blog posts that point out flaws in those articles (regardless of how obvious they may be to people in the field). Such a feature has the potential to end up being used as a public review forum.