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One of the questions folks tend to ask me is some form of, "when can I expect my cellphone to contain a quantum co-processor?" That gives me an excellent opportunity to tell them everything that I know about cryogenic refrigerators (which only takes a minute).

The chips we make (speaking directly of D-Wave, but afaik this is true of all superconducting QC efforts) would cost pennies if we produced them at scale. But the surrounding machinery is extremely complex, and very expensive to manufacture -- and scale would only get you so far. My rough understanding of refrigeration is that the temperature differential strongly depends on the length of the heat exchanger. Qubits are famously sensitive to noise; and blackbody radiation gives an inescapable dependence between noise and temperature. In short, a miniaturized fridge would be necessarily hot, and therefore too noisy to perform quantum computation!

So the sad news is that, barring some major developments, we may never have miniature quantum computers. In the foreseeable future, hardware costs will be measured in millions of dollars. So even if you're a millionaire, you probably don't want to buy a quantum computer. If you work for a university, a national laboratory, or a major corporation, you might try to convince your organization to purchase a quantum computer. If you succeed in that pitch, you'd almost certainly need to share it with your colleagues over a network.

So to me, an industry insider, it feels that public access to quantum computing is almost necessarily QCaaS.

I wonder if we had the same perspectives when comptuers were first established in the 50's/60's.

We couldn't possible foresee how these monster of a machines could possible fit in the palm of our hands and yet, now, it's hard to see how we couldn't see that far in front of us.

We had this famous quote from IBM but, I wonder if as an industry this was a common perspective. Or wether between those who were building these machines could foresee where we'd be now? Is there some one in Quantum Computing who has the intelligence and creativity to think, nah, we'll have giant refrigerated quantum computing mobile phones in 5x decades time (I understand Quantum Computers wouldn't make great phones I'm just drawing baseless comparisons :) )

"I think there is a world market for maybe five computers."

Thomas Watson, president of IBM, 1943

= = = =

I only found out about wolframalpha a month ago and I'm still in awe of it. Quantum computing as a service? No idea what I'm going to want to do with it. But I re-watch this video by Veritasium and Andrea Morello from UNSW a couple of times a year to just remind myself how much I don't know.


Just as an aside, that quote is likely apocryphal. No one has ever been able to find actual evidence that he said this, and those close to him have rejected it as a false attribution. It was being recognized as a myth way back in the 1970s.

Even if he had said it, it was a very accurate statement at the time. Gordon Bell has noted that at the time he is claimed to have made that statement, it would have held essentially true for a decade. As something that would have likely been said (if said at all) in discussions around IBM's near-future business plans, or a sort of market analysis of the conditions at the time, it makes perfect sense.

See, this is why I would suck as a contestant on QI. Thank you. :)

Cooling chips to around room temp was an evolutionary process. Cooling chips to near absolute zero is another ball of physics entirely. I suspect it is like trying to have a pocket sized NMR machine, which needs liquid helium cooling etc. Those things can’t just be scaled down to pocket size.

What about photonic quantum computers? You can access quantum mechanical effects at room temperature with photonics. I don’t know if it’s more difficult to use them for computing though

Yes, because photons don't interact with each other

Are you supporting or refuting my thesis? Assuming the latter, just because photons as particles don’t “interact” (by which I presume you mean they are bosons) doesn’t mean you can’t get interesting multi particle quantum results with photons. See for example https://en.m.wikipedia.org/wiki/Hong–Ou–Mandel_effect

I'm not sure if it's up to the task (yet?), but thermoelectric coolers are routinely used for CCDs that operate below -80 °C (an overview: https://www.azom.com/article.aspx?ArticleID=14681). I suspect someone will come up with a solution once the technology starts to mature.

At those temperatures things get weird. Cryocoolers are established technology, but anything colder than the xx K range very quickly stops being easy in any way.

That said, LH2 temperatures aren't really hard and can easily fit in a 2U rackmount device, providing power/classical-RF uses of type2 superconductors. Think EMI shielding, power conditioning, ~50 GHz traces that can span a full backplane without fancy signal conditioning, etc.

Thermoelectric coolers are not even able to keep up with modern CPUs. Or rather, they can, but they are very energy hungry. As much or more so than the CPU itself.

Mostly: thermometric coolers are bad for >50K difference and >10W heat flux on the cold side. Most uses are better off with a sterling cooler or maybe even an absorption refrigerator, which can have no mechanical parts (just fluids, plumbing and heat exchanges) and could theoretically provide human-centric AC/refrigeration based on server waste heat.

Forgive my ignorance with this question. Would it be possible to run these quantum chips in space? Space is cold and quiet so maybe that’s cheaper at scale.

In general, you shouldn't think of space as being cold for intuitive hot-to-cold heat transfer. For example, the metallic side of a space ship would not be anywhere near 0K, whereas if you had a metal plaque between a liquid at around 0K and your hand, it would be.

It is very hard to dissipate heat from a solid object into space. This is not true for our bodies on the other hand, but that is more to do with pressure - if you expose cells to the Void of space, most liquids inside would quickly expand in size and essentially boil, consuming large amounts of heat to go through the phase transition from liquid to gas, thus quickly cooling surrounding tissue. You could theoretically use this to create evaporation-based heating, but you would have to transport vast quantities of water that would quickly be used up, since there is no hope of collecting them back most likely.

Shedding heat in space is a huge problem because you can only radiate it. Depending on the refrigeration requirements there may be too much excess heat to make it feasible.

You’d probably lose a lot of the advantages because you lose the naturally extremely effective radiation shielding of the earths magnetic field and atmosphere.

You'd probably always have to stay in the shadow of some celestial body and the 3K microwave background would be an issue as well that would have to be solved.

Maybe something a tiny little black hole could fix?

There’s just got to be a way, there’s no way we can just give up.

I’m fairly sure decades ago people assumed we may never have tiny computers in our pockets with the same certainty you have now.

This is what it means to be crazy enough to change the world.

On the other hand, many people assumed we'd have flying cars and colonies on Venus.

Oh, and fusion reactors.


Now that I think of it, there was a lot of variation in predictions of computing. But I would say that it's been pretty common for science fiction to describe technology 30 years out somewhat accurately, probably because it has inspired the actual tech in a self-fulfilling way.

So, in the 40s, a spaceship was envisioned able to carry only calculators and slide rules, with a radio link to a big central computer. That wasn't far off of how things developed in the 60s and 70s. But I think by the 60s and 70s, people were imagining pocket computers and tablets and such and that had a huge effect on people actually designing them when it was possible.

If people’s assumptions tend to be wrong then we can expect to someday have mini quantum computers since people assume they are impossible.

See my addition. My point is that some predictions are right and some are wrong.

> There’s just got to be a way, there’s no way we can just give up.

By no means do I intend to discourage progress! I wouldn't do the work that I do if it wasn't so difficult. I did hedge, a bit: "may never," "foreseeable future," "without major developments."

The fridge is just one major obstacle. There's a plethora of physics, engineering, and mathematical challenges out there impeding progress. Get to work!

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