Monthly Archives: March 2013

The Dark Horse of Quantum Computing

D-Wave, Quantum Computing, ,

Updated below.

Recently, Science magazine prominently featured Quantum Information Processing on their cover:

 

The periodical has a great track record in publishing on QIS, and this is the main reason why I subscribe to it.

Unfortunatelly, reading this issue, yet again drove home what a dark horse enterprise D-Wave is. And this is despite some recent prominent news, that D-Wave effortlessly passed a test devised to check for the quality of entanglement that they realize on their chip. There is hardly any lingering doubt that they managed to leverage real quantum annealing, yet, neither their approach, nor adiabatic quantum computing, is featured at all in this issue of Science.  In the editorializing introduction to the cover story dubbed “the Future of Quantum Information Processing” these fields aren’t even mentioned in passing.  Are we to conclude that there is no future for adiabatic quantum computing?

This I found so puzzling, that it prompted me to write my first ever letter to the editors of Science:

The Science journal has been invaluable in the past in advancing the QIS field, publishing an impressive roster of ground breaking papers. Yet, it seems to me the editorializing introduction of the March 8th cover story by Jelena Stajic dropped the ball.

If QIS is prominently featured on the cover of your journal shouldn’t the reader at least expect a cursory exposition of all prominent developments in the entire field? There is nothing wrong with the authors of the paper on the superconducting Josephson junctions approach to QC, restricting themselves to universal gate based architectures. Nevertheless, at least in the accompanying editorial, I would have expected a nod towards adiabatic quantum computing, and approaches utilizing quantum annealing. This oversight seems all the more glaring as the latter already resulted in a commercial offering.

Sincerely,

Henning Dekant

Disclaimer: I am not affiliated with the company D-Wave, which ships the first commercial quantum computing device, just puzzled that an exemplary publication like Science doesn’t feature the entire spectrum of approaches towards quantum computing.

My bet with a sceptical QC and CIS expert is still outstanding, and in my exchange with him, he mentioned that he didn’t expect D-Wave to pass this first entanglement hurdle. The next one to pass now is the matter of actual benchmarking against established chip architectures.

If D-Wave’s One cannot outperfom a conventional single-threaded architecture I’ll lose 4 gallons of maple syrup, but even if that was to come to pass, it wouldn’t spell the end for D-Wave, as it’ll be just a matter of increasing the qbit density until a quantum annealing chip will surpass conventional hardware. The latter only improves linearly with the integration density, while a quantum chip’s performance grows exponentially with the numbers of qbits that it can bring to bear.

Update:

Without further comment, here is the answer that I received from Science:

Thank you for your feedback regarding the introductory page to our recent QIP special section. I appreciate the point you are making, and agree that quantum annealing is an important concept. Let me, however, clarify my original reasoning. The Introduction was aimed at the general reader of Science, which, as you are aware, has a very broad audience. It was not meant to be an exhaustive account, or to complement the reviews in the issue, but rather to serve as a motivation for covering the topic, and hopefully to induce a non-specialist reader to delve into the reviews, while introducing only a minimal set of new concepts.

I hope that this is helpful, and once again, I am grateful for your feedback.
Best regards,
Jelena Stajic
Associate Editor

Fun Stuff: When Shakespeare meets Schrödinger

Quantum Mechanics, ,

Shakespeares_cat

In the associated LinkedIn discussion to my previous post, commenters had some fun with the Shakespeare inspired headline. Clearly, if Shakespeare would have known Quantum Mechanics and the superposition that holds Schrödinger’s cat in limbo, some of the classic pieces would have sounded slightly different. Dr. Simon J.D. Phoenix had this brilliant take on it:

“To be, or not to be, or maybe both

–that is the question:
Whether ’tis nobler in the mind to calculate
The slings and arrows of outrageous quanta
Or to take arms against a sea of interpretations
And by opposing end them.
To sleep, to wake —
No more, but both –and by a sleep to say we end
The headache, and the thousand natural shocks
That Bohr bequeathed. ‘Tis a consummation
Devoutly to be wished. To wake, to sleep–
To sleep–perchance to dream: ay, there’s the rub,
For in that sleep of Copenhagen what dreams may come
When we have shuffled all our mortal calculations,
Must give us pause. There’s the Aspect
That makes calamity of so entangled a life.
For who would bear the Bells and Wittens of time,
Th’ position’s wrong, the proud momentum’s contumely
The pangs of despised theory, the quantal law’s decay,
The insolence of academic office, and the spurns
That patient merit of th’ unworthy unlearned takes,
When he himself might his quietus make
With a bare bra-ket? Who would fardels bear,
To grunt and sweat under a weary state vector,
But that the dread of something not quite real,
The undiscovered counterfactual, from whose bourn
No traveller returns, puzzles the will,
And makes us rather bear those classical ills we have
Than fly to others that we know not of?
Thus common sense does make cowards of us all,
And thus the native hue of resolution
Is sicklied o’er with the pale cast of Heisenberg,
And enterprise of great position and momentum
With this regard their currents turn awry
And lose the name of action. — Soft you now,
The fair Dirac — noble and precise, in thy orisons
Be all my spins remembered.”

Nobel Laureates on the QM Interpretation Mess

Popular Science, Quantum Mechanics, ,

Update:  Perusing the web I noticed that John Preskill [not yet a Nobel laureate 🙂 ] also blogged on the same survey.  Certainly another prominent voice to add to the mix.

~~~

In the LinkedIn discussion to my earlier blog post that was lamenting the disparate landscape of QM interpretation, I had Nobel laureate Gerard ‘t Hooft weighing in:

Don’t worry, there’s nothing rotten. The point is that we all agree about how to calculate something in qm. The interpretation question is something like: what language should one use to express what it is that is going on? The answer to the question has no effect on the calculations you would do with qm, and thus no effect on our predictions what the outcome of an experiment should be. The only thing is that the language might become important when we try to answer some of the questions that are still wide open: how do we quantize gravity? And: where does the Cosmological Constant come from? And a few more. It is conceivable that the answer(s) here might be easy to phrase in one language but difficult in another. Since no-one has answered these difficult questions, the issue about the proper language is still open.

His name certainly seemed familiar, yet due to some very long hours I am currently working, it was not until now that I realized that it was that ‘t Hooft.  So I answered with this, in hindsight, slightly cocky response:

Beg to differ, the interpretations are not more language, but try to answer what constitutes the measurement process. Or, with apologies to Ken, what “collapses the wave function”: The latter is obviously a physical process. There has been some yeoman’s work to better understand decoherence, but ultimately what I want to highlight is that this sate of affairs, of competing QM interpretation should be considered unsatisfactory. IMHO there should be an emphasis on trying to find ways to decide experimentally between them.

My point is we need another John Bell.  And I am happy to see papers like this that may allow us to rule out some many world interpretations that rely on classical probabilities.

So why does this matter?  It is one thing to argue that there can be only one correct QM interpretation, and that it is important to identify that one in order to be able to develop a better intuition for the quantum realities (if such a thing is possible at all).

But I think there are wider implications, and so I want to quote yet another Nobel laureate, Julian Schwinger, to give testament to how this haunted us when the effective theory of quantum electrodynamics was first developed (preface selected papers on QED 1956):

Thus also the starting point of the theory is the independent assignment of properties to the two fields, they can never be disengaged to give those properties immediate observational significance. It seems that we have reached the limits of the quantum theory of measurement, which asserts the possibility of instantaneous observations, without reference to specific agencies.  The localization of charge with indefinite precision requires for its realization a coupling with the electromagnetic field that can attain arbitrarily large magnitudes. The resulting appearance of divergences, and contradictions, serves to deny the basic measurement hypothesis.

John Bell never got one of these, because of his untimely death.