Is it a QC?

This post began its life as a supposedly brief update to my earlier post [^] on D-Wave’s paper, but the text soon grew long enough to become a separate post by itself. So, here we go.

Predictably, a controversy concerning the D-Wave paper (and its coverage in the media) came up soon later, at Prof. Scott Aaronson’s blog [^]. At 300+ comments (as of publishing this post), there is a lot of speculation, skepticism, and hilarity of the usenet/slashdot kind going on over there, apart from also some commentary.

However, as far as I am concerned, the most interesting part in (re) examining the paper and the related claims, was the following doubt which the controversy helped highlight: whether this particular D-Wave device had actually succeeded in exploiting, at least in part, the specifically quantum-mechanical effects, or not; whether there was an engineering success in controlling, at least in part (and to a practically significant extent), the quantum decoherence effects, or not.

The controversy was not entirely unexpected; recall this bit from the first New York Times story [^]:

““There is no sense in which this is the definitive statement about quantum computing,” Ms. McGeoch said. “I’m more interested in how well it works, not whether or not it is quantum.””

Though they called it a “quantum computer” (and I repeated the term), the term obviously was being used in a somewhat loose sense.

And, yes, I will admit it: without going through the paper well, I rather relied on the peer-review process, and so certainly thought, at least at the time of writing my earlier post, that D-Wave had a more impeccable and comprehensive result than what now seems to be the case.

But returning to who is interested in what: Well, as far as I am concerned, the issue of whether they got any speed-up or not, is strictly secondary—it’s “just” a consequence!

(In fact, I even don’t care if a QC research group cannot factor any composite beyond some single digit number, as of today. So long as they demonstrate a practically significant control of decoherence, and some clue about how they expect to scale it up, even their success in factoring only a small number would still make sense to me. Any future value of a QC in cracking open secret codes, or in designing better drugs through quantum chemical modeling, would be “just” a consequence, as far as I am concerned.)

To my mind, the real issue is: whether D-Wave succeeded in building a quantum computer (with some promise of some significant levels of a future scalability), or not.

So, from this angle, the most significant comment at Aaronson’s blog has been this one [^] by Prof. David Poulin, alerting the appearance of a paper by John Smolin and Graeme Smith, both of IBM, at arXiv, yesterday [^]. In case you are wondering whether to give this paper a read or not, let me remind you that IBM is a (corporate-sector) competitor to D-Wave. And, if that isn’t going to help, let me quote a bit from the main text of the paper:

“Since classical simulated annealing is intrinsically random and ‘quantum annealing’ is not…”

[emphasis mine]

and a line from their conclusions section:

“The deterministic nature of quantum annealing leads to rather different behaviors than the random processes of simulated annealing.”

[emphasis mine]

Interesting, no? (LOL!)

Of course, my own interests are in the foundations of QM, in providing a proper conceptual explanation for (and even mathematical expression to) the specifically quantum-mechanical effects/paradoxes/oddities, and not in the details of this or that quantum-mechanical process, whether it has some/a lot of/very great merit in building a scalable QC, or not.

So, I am not going to look too closely into this IBM paper either. Or provide a commentary on the position(s) it takes, its merits, or any polemical value it provides in this controversy (or in any other!). Or, add in any other way, to this D-Wave-related  controversy. … That way, I am not totally averse to controversies, but as far as this one goes, I find that it is a greater fun taking a ring-side view, here.

For another thing, these days, I am also thinking of quite different (and between them, somewhat unrelated) things: diffusion, small dams and water resources engineering/management, and tensors. Expect a post or two on these topics, soon enough.

So, all in all, even if I am having fun watching this controversy develop and grow, I guess I am going to sign off blogging about it. I won’t write any further on this topic, unless, of course something even more funny (or definitive, even if a bit serious) emerges from it.

[E&OE]

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One thought on “Is it a QC?

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