Comments for Wavewatching http://wavewatching.net Observations on the nascent quantum computing industry & physics Sun, 21 Sep 2014 18:45:25 +0000 hourly 1 http://wordpress.org/?v=3.9.2 Comment on What Defines a Quantum Computer? by Henning Dekant http://wavewatching.net/2014/09/21/what-defines-a-quantum-computer/#comment-81751 Sun, 21 Sep 2014 18:45:25 +0000 http://wavewatching.net/?p=3287#comment-81751 A notion certainly anathema to most complexity theorists and physicists, Hava Siegelmann is probably one of the few computer scientists who think similarly.

She wrote a monograph on this: Neural Networks and Analog Computation: Beyond the Turing Limit (Progress in Theoretical Computer Science)

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Comment on What Defines a Quantum Computer? by Kingsley Jones http://wavewatching.net/2014/09/21/what-defines-a-quantum-computer/#comment-81750 Sun, 21 Sep 2014 06:41:01 +0000 http://wavewatching.net/?p=3287#comment-81750 Yes, there is confusion. What Deutsch did not realise, or those that came later is that quantum computing can be fully embedded in classical computing.

I don’t know when the penny will finally drop.

It has been decades now and people still have not seen it.

I remain flabbergasted :-)

However, I am not surprised. It takes a lot to prise the scales from people’s eyes.

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Comment on The Church of D-Wave by What Defines a Quantum Computer? | Wavewatching http://wavewatching.net/2014/03/31/the-church-of-d-wave/#comment-81749 Sun, 21 Sep 2014 04:11:49 +0000 http://wavewatching.net/?p=3060#comment-81749 […] In the quantum computing domain, things are less clear cut. In my earlier post where I tried my hand at a quantum computing taxonomy, I focused on maturity of the technology, less so on the underlying theoretical model. However, it is the dichotomy in the latter that has been driving the heated controversy of D-Wave's quantumness. […]

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Comment on The Business Case for D-Wave by Quax http://wavewatching.net/2014/07/22/the-business-case-for-d-wave/#comment-81748 Sat, 20 Sep 2014 14:13:01 +0000 http://wavewatching.net/?p=3222#comment-81748 If you believe that they have and that 500 qubits are comparable to billions of bits, then you believe that D-wave is achieving a quantum speedup, and not just a “modest” one.

If I thought that was true I wouldn’t have conceded the bet I had with Mathias Troyer, and wouldn’t be short of four fine jugs of Maple Syrup :-)

Look, I am really not quite sure what we are arguing about at this juncture.

The Troyer et al. paper shows that there is no evidence for quantum speed-up (yet?) in the D-Wave One, on the other hand it also shows that it performs as fast as a current multi-core CPU with a hand-optimized annealing code. And yes, the latter should have billions of transistors, so I fail to see your point.

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Comment on The Business Case for D-Wave by aramharrow http://wavewatching.net/2014/07/22/the-business-case-for-d-wave/#comment-81747 Sat, 20 Sep 2014 09:09:34 +0000 http://wavewatching.net/?p=3222#comment-81747 I wouldn’t say they’ve “caught up” with conventional chips, or that they have established faster than linear scaling.

If you believe that they have and that 500 qubits are comparable to billions of bits, then you believe that D-wave is achieving a quantum speedup, and not just a “modest” one.

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Comment on The Business Case for D-Wave by Henning Dekant http://wavewatching.net/2014/07/22/the-business-case-for-d-wave/#comment-81746 Fri, 19 Sep 2014 19:16:56 +0000 http://wavewatching.net/?p=3222#comment-81746 I’m now somewhat lost. “Rising integration density” just means more qubits per chip, right?

Yes.

If you believe quantum speedup can be achieved by the D-wave architecture, then this grows more rapidly than c * N for any constant c.

This, to me, is the missing link in our conversation that resulted in the confusion.

In my mind a modest better than linear grows in performance from one D-Wave generation to the next wouldn’t necessary constitute hard evidence for quantum speed-up.

The Chimera architecture hasn’t changed significantly, I don’t think.

When last I spoke to Geordie he mentioned that they are constantly changing the details of the architecture even if the underlying Chimera architecture stays the same.

That’s why I wouldn’t rule out that D-Wave may simply take advantage of incremental smarter engineering of their hardware as they learn to control the fab process better, and that this may contribute to the faster than silicon performance gains. After all their current structures are gigantic in comparison to what’s in your laptop’s CPU.

To me it seems to be an established fact that they realized these faster performance gains, but I am not comfortable to speculate what enables this trend without having more data.

From my point of view, you argue in a somewhat backwards manner. To you any such gain would proof quantum speed-up, yet since research on the D-Wave One has not established such speed-up, you argue that D-Wave shouldn’t have been able to make better progress in terms of performance than classical hardware. The latter though is in contradiction to the fact that they manged to catch up to conventional chips within ten years.

Is there something ‘quantum’ to the magic that allowed them to play catch-up? Maybe, but in my blog post I argue that this doesn’t really matter as long as they can continue on this trajectory. That’s all it takes to make this commercially interesting.

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Comment on The Business Case for D-Wave by aramharrow http://wavewatching.net/2014/07/22/the-business-case-for-d-wave/#comment-81745 Fri, 19 Sep 2014 16:02:06 +0000 http://wavewatching.net/?p=3222#comment-81745 I’m now somewhat lost. “Rising integration density” just means more qubits per chip, right? The Chimera architecture hasn’t changed significantly, I don’t think.

The question is how the computational power of D-wave scales with the number of qubits N. I am 99% sure that the power costs can be modeled as a + b N, for some constants a,b, and that we are currently in the regime where a >> bN. For computational power, if you believe quantum speedup can be achieved by the D-wave architecture, then this grows more rapidly than c * N for any constant c. The presence of quantum speedup in the D-wave architecture is still an open question, both empirically and theoretically. Empirically, Alex Selby’s code (among others) is still much faster. Theoretically, no examples of speedup have been proved, even for a hypothetical noise-free version of the D-wave architecture. Counter-arguments can be made, but you should at least acknowledge that claiming a quantum speedup for D-wave is highly controversial.

I realize that the D-wave promotional materials present this an uncontroversial fact. You should understand that they are literally selling something, and that the science press is usually too credulous about these things.

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Comment on The Business Case for D-Wave by Henning Dekant http://wavewatching.net/2014/07/22/the-business-case-for-d-wave/#comment-81744 Fri, 19 Sep 2014 15:49:39 +0000 http://wavewatching.net/?p=3222#comment-81744 You are now saying that D-Wave’s chips exhibit quantum speedups.

Just to be clear on this, observing that their performance grows faster with rising integration density than classical chips implies to you that there must be a quantum speed-up?

Let me just recap briefly. The apparent lack of increased energy usage is because of the large constant term.

That’s entirely possible but without more data I don’t consider this is a foregone conclusion.

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Comment on The Business Case for D-Wave by aramharrow http://wavewatching.net/2014/07/22/the-business-case-for-d-wave/#comment-81743 Fri, 19 Sep 2014 14:46:52 +0000 http://wavewatching.net/?p=3222#comment-81743 You are now saying that D-Wave’s chips exhibit quantum speedups. This is in fact controversial among experts. But leaving that aside for now, the point of your blog post was that quantum speedup was not necessary for D-wave’s devices to be valuable. This is the point I’m arguing against.

Let me just recap briefly. The apparent lack of increased energy usage is because of the large constant term. It’s like saying that adding RAM to my laptop doesn’t increase its power use because the screen uses so much more power. Here RAM:qubits and screen:fridge. For it to be different, you need quantum speedup.

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Comment on The Business Case for D-Wave by Henning Dekant http://wavewatching.net/2014/07/22/the-business-case-for-d-wave/#comment-81742 Fri, 19 Sep 2014 14:37:11 +0000 http://wavewatching.net/?p=3222#comment-81742 The debate about whether there is a quantum speedup, or whether they have “caught up with conventional hardware”, is a different and much longer one. Presumably this is what you are saying when you say that the performance is growing nonlinearly. Most experts would say that this claim is speculative at best..

What I am trying to say is really quite simple, and apparently I am not saying it very well.

The early D-Wave chips were no match for classical hardware. They then doubled their chips’ density pretty consistently every 15 months, which is slightly faster than Moore’s law. But not fast enough for them having caught up on this basis alone. So the annealing scheme they implement seems to gain more performance as the density increases. I.e. D-Wave receives more of a performance boost when doubling the qubits than you get when doubling the transistors on a conventional chip. From my point of view this observation shouldn’t be very controversial.

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