D-Wave Withdrawal Relief

AAFor anybody needing an immediate dose of D-Wave news, Wired has this long, well researched article (Robert R. Tucci summarized it in visual form on his blog). It strikes a pretty objective tone, yet I find the uncritical acceptance of Scott Aaronson’s definition of quantum productivity a bit odd.  As a theorist, Scott is only interested in quantum speed-up. That kind of tunnel vision is not inappropriate for his line of work, just an occupational hazard that goes with the job, but it doesn’t make for a complete picture.

Other than that, the article only has some typical minor problems with QM.

At this point, you don’t really expect a journalist to get across how gate model quantum algorithms work, and the article actually does this better than most. But the following bit is rather revealing; The writer, Clive Thompson, describes visually inspecting the D-Wave chip:

Peering in closely, I can just make out the chips, each about 3 millimeters square. The niobium wire for each qubit is only 2 microns wide, but it’s 700 microns long. If you squint very closely you can spot one: a piece of the quantum world, visible to the naked eye.

SQUIDs for magnetometers don’t have to be very small. (Photo approximately to scale – as indicated by the handwriting on this lab sample). This is because for this application you want to measure the magnetic flux encompassed by the loop.

Innocuous enough quote, and most physicists wouldn’t find anything wrong with it either, but therein lies the rub. SQUIDs can be fairly large (see photo to the right).

Any superconducting coil can harbour a coherent quantum state, and they can be huge.

The idea that quantum mechanics somehow only governs the microcosm has been with us from its inception, because that’s what was experimentally accessible at the time i.e. atomic spectra.  But it is a completely outdated notion.

This is something I only fully came to grasp after reading Carvar Maed’s brilliant little book on Collective Electrodynamics. In it, he makes a very compelling case that we are due for another paradigm change.  To me, the latter means dusting off some of Schrödinger’s original wave mechanics ideas. If we were to describe a simple quantum algorithm using that picture, there’s a much better chance to give non-physicists an idea of how these computation schemes work.

 

12 thoughts on “D-Wave Withdrawal Relief

  1. Hi Henning: Thanks for this blog post. I, literally read it, just before I saw your new post and came roughly to the same conclusions that you did!. In fact, I expressed my sentiments to them, in a brief blurb in their “Comments” section!. Thanks again.

    1. Didn’t pick up on the article before I saw Bob’s post. Didn’t even realize that Wired survived the .com era 🙂

  2. On the visualization front check out this tool from Google:

    http://qcplayground.withgoogle.com/#/home

    I agree with your sentiments regarding the confusion which has grown up around use of the terms “quantum” and “classical” to describe micro and macro behavior.

    Mead does give some excellent physical examples of how this is a well-outdated notion. One would think this understanding would have penetrated in quantum computing, but for some reason it has not. Folks seem to have taken the bait that the single concept of “decoherence” is sufficient to understand what goes on with quantum measurements. As a result, we have seen a belief grow up that the quantum theory in its present form is sufficient to fully explain the underlying phenomena.

    It seems to me that this is (perhaps) why there is such confusion as to whether the superconducting chip in the D-Wave device actually does exhibit quantum mechanical properties. The cult of decoherence as an explanation for the non-observation of Schroedinger cat states has convinced people that strong quantum correlations could not be present. However, the argument based on decoherence as an explanation of individual events has always fallen short of an important observational fact.

    We do not see an “ensemble” result. We see individual results with a certain statistical distribution.

    That was always the criticism of Einstein and people have resorted to ever more elaborate mental gymnastics about how to reconcile the assumption of quantum jumps with coherent behavior.

    Now I think we are just at the start of the real work and real opportunity.

    Experimental observation, manipulation and control of coupled flux qubits or coupled quantum dots is now within reach – as demonstrated by the D-Wave engineers themselves. Hence we now have the ability to actually probe the temporal behavior of these weakly open (nearly isolated) systems.

    In a proper scientific discipline this would give theorists some pause on their grounds for confidence that we can say, with certainty, what is going on in that place where traditionally we invoked a “jump”.

    Perhaps there is no jump at all? Perhaps Schroedinger was right all along? Perhaps the actual real ground for quantum reality is a wave in configuration space for which we only see a shadow?

    Perhaps, as I have argued elsewhere, we only see the quasi-classical field represented by the one-body density – the continuum fields equivalent of a simultaneous measurement of all “particles” present?

    Visualization tools will help understand how to translate that hypothesis to real-world models.

    Equally, simulation tools and real-world coupled qubit circuits will help us devise the tests.

    For too long, physicists have assumed they know the right theory to describe these specific domain of behavior. However, in truth they were always phenomenological patches: quantum jumps; transition probability rules and hand-wavy arguments that a diagonal density matrix is equivalent to the real world observation of individual events with certain stochastic properties.

    Dogma won’t do anymore.

    The people actually want some Science and the time is ripe to deliver it.

    1. Playing around with how to simulate wave equations (and what makes for the best Laplacian) gave me a new appreciation for the wave mechanics aspect, and the value of visualization. I.e. in my mind’s eye something likes Shor’s algorithm looks more like an engineered tsunami that when measured at the right time gives you the location of the main wave crest with very high probability, which in turn gives you the right factorization answer.

      I think this picture also gives you more of an appreciations why it is so hard to build something like gate based Quantum Computing. Essentially these algorithms are the equivalent to freak waves (which BTW are describe by a great word in German: Kaventsmann).

  3. That’s interesting as I worked on HTS materials a long time ago (at the time when enthusiasts hoped we would soon have superconducting cables everywhere).

    The idea of the giant quantum state felt like a normal thing to me, and you could ‘explain’ it in a rather simple way using the phenomenological model of Ginzburg-Landau.

    When we did ‘science events’ for the public at the university, a demo of Meissner-Ochsenfeld effect was always given – which should also make the ‘delicate quantum effects’ quite palpable.

    1. Josephson junctions have always been my favorite quantum system ever since I gave a short seminar presentation on them, but I never did much hands on HTC work (although I got to play a bit with liquid nitrogen and got to see the Meissner-Ochsenfeld effect, which never fails to impress).

      But it never quite clicked for me before reading Carvar Maed books that this really means that we’re kind of stuck in the wrong paradigm with regards to QM.

      As to HTC cables etc. that’s a good idea for another blog post, it took a long time but slowly most of the technological challenges of working with these pesky ceramic materials have been overcome. If I am not mistaken the longest HTS transmission cable now covers just shy of a kilometers, and there are some interesting ideas out there to power ships with huge HTS motors.

  4. Thanks for your comments and for the links you supplied. I’d like to call attention to the following work:

    ‘The interpretation of quantum mechanics: Dublin seminars (1949-1955),’ by Schrödinger.

    Therein we find the following remarks, which jibe with my own views to a remarkable degree.

    “What this something is cannot be said; by calling it matter or field or whatnot, we just give it a name. The relevant point is that it is not supposed to have any other properties but geometrical configuration, changing in time according to certain “laws of nature.” It is not in itself yellow or green, sweet or cold. If parts of it appear to us so, there is no hard, indubitable fact to make this judgment true or false.

    This view is strongly supported by our analysis of actual experimental procedure, and it is attractively simple. It carries us comfortably a long way, indeed so long, that we may have forgotten its artificiality, when we meet the obstacles that it renders unsurmountable. So it is better to ask the naive but very pertinent question right away: how do red and yellow, sweet and hot come in at all? Once we have removed them from our “objective reality,” we are at a desperate loss to restore them. We cannot remove them entirely, because they are there, we cannot argue them away. So we have to give them a living space, and we invent a new realm for them, the mind, saying that this is where they are, and forgetting the earlier part of the story—all that we have been talking about till now—is also in the mind and nowhere else. But deeming it to be something else—objective reality—we run against the unanswerable question: how does matter act on mind, to produce in it the sensory qualities—and also how does mind act on matter, to move it at will? These questions cannot, so I believe, be answered in this form, and they owe their embarrassing form precisely to our having posited an objective reality which is a pure geometrical scheme of thought and deprived of everything real given by experience.”

    http://bit.ly/1noTrp4

  5. Henning, there seems to be a small glitch in how you have your WordPress set up. When I go to the homepage of the blog, I get this May 2014 entry at the top instead of the latest June 2014 entries

    1. Thanks for letting me know. Not sure what it causing this. Don’t see it on my end, but suspect some trouble with my page caching plug-in.

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