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Dreaming of the Quantum Singularity with MIT

On my nightstand right now is Richard Feynman's _The Pleasure of Finding Things Out_, a short and sweet collection of essays and talks from the modern physics guru. And one of those talks is about Feynman's days working on the bomb at Los Alamos.
Image: Christine Daniloff/MIT

On my nightstand right now is Richard Feynman's The Pleasure of Finding Things Out, a short and sweet collection of essays and talks from the modern physics guru. And one of those talks is about Feynman's days working on the bomb at Los Alamos. In it, he's remembering managing a small array of OG IBM computers to figure calculations about just how much energy an atomic bomb is actually going to release. It took months of kicking long stacks of punch cards through different machines, big unweildy mechanical beasts all working on different elements of arithmatic (addition, multiplication, etc), to get answers. Months.

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That was only about one human lifespan ago. In the '40s, those computers were generally being used for business accounting; figuring out The Bomb was likely the hardest calculation of the time. And I bring this up because we have a new one and, possibly, the future of quantum computing hinges on being able to solve it.

Yesterday, MIT announced that it will present a paper in June outlining the first quantum computing experiment with the capability to prove that quantum computers can do things that classical computers, from your dual-core whatever to Feynman's room-filling dinosaurs, just plain can't. (Yes, for all of the quantum computing hype, this hasn't been a given.) The moment, when we outdo classical computers, has a name: the "quantum singularity." Ohhhh, ahhhhh.

The MIT experiment is based on a University of Rochester experiment from the '80s involving what's known as a beam splitter. Simply: fire a beam of light at said beam splitter, which sends the beam in two different directions, and if two of the beam's constituent photons—photons make up light, OK—hit the splitter at the same time, than they'll both go the same direction. They're not attached in any way, or by anything unseen that we know of in classical nothing-faster-than-light physics, but they're sharing something. There's no explanation for why it happens, but it does. Quantum mechanics is just mad weird.

Let's let MIT explain their version of the experiment:

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The MIT researchers' experiment would use a larger number of photons, which would pass through a network of beam splitters and eventually strike photon detectors. The number of detectors would be somewhere in the vicinity of the square of the number of photons — about 36 detectors for six photons, 100 detectors for 10 photons.

For any run of the MIT experiment, it would be impossible to predict how many photons would strike any given detector. But over successive runs, statistical patterns would begin to build up. In the six-photon version of the experiment, for instance, it could turn out that there's an 8 percent chance that photons will strike detectors 1, 3, 5, 7, 9 and 11, a 4 percent chance that they'll strike detectors 2, 4, 6, 8, 10 and 12, and so on, for any conceivable combination of detectors.

Calculating that distribution — the likelihood of photons striking a given combination of detectors — is an incredibly hard problem. The researchers' experiment doesn't solve it outright, but every successful execution of the experiment does take a sample from the solution set. One of the key findings in Aaronson and Arkhipov's paper is that, not only is calculating the distribution an intractably hard problem, but so is simulating the sampling of it. For an experiment with more than, say, 100 photons, it would probably be beyond the computational capacity of all the computers in the world.

So, in the stupidest terms I can come up with, we're trying to figure out the probability of the photons hitting the detectors if we're using a whole lot of photons. Which is a problem the best computer in the world couldn't handle. But using this sort of sub-computer "apparatus" it might just be possible. Might.

Maybe the most important takeaway from all of this is that building this thing and it being successful is easier than building an actual quantum computer, at least a quantum computer in the revolutionary sense that gets all the hype. It's a reality check. I get blasted with like 15 new items every day for "quantum computer" via Google Alerts and we're still in sub-baby steps in terms of making one. But, if the MIT experiment is successful, it points to us actually being able to and that physics isn't wasting its time with the idea.

Related:
Quantum Experiment Brings Us Closer To Super-Fast Computers
Quantum Computers Take Another Small Step Forward
Science Creeps Even Closer To Quantum Computing

Please explain it better to this writer at michaelb@motherboard.tv