There are rumors that Google has achieved quantum supremacy. According to Scott Aaronson, my go-to person for all things quantum mechanics, we weren't meant to know about this yet. As Scott says on his blog:

As the world now knows, Google is indeed preparing a big announcement about quantum supremacy, to coincide with the publication of its research paper in a high-profile journal (which journal? you can probably narrow it down to two). This will hopefully happen within a month. Meanwhile, though, NASA, which has some contributors to the work, inadvertently posted an outdated version of the Google paper on a public website. It was there only briefly, but long enough to make it to the Financial Times, my inbox, and millions of other places. Fact-free pontificating about what it means has predictably proliferated.

Quantum supremacy sounds like a big deal, and eventually it probably will be. It means performing a calculation using a quantum computer that would be either impossible for a conventional computer, or would take it years. If the problem is actually useful, say decrypting some conventionally unbreakable code, so much the better. It seems that the problem Google solved is not useful in the slightest. Ideal problems to solve in these early days are ones that are hard to solve, but where deciding whether the solution is correct is simpler. An example of a problem like this is factorizing large numbers. This is very hard, but verifying tat the factors do indeed multiply up to the original number is easy.

I'm not going to try and explain what the problem Google solved was, since it is so obscure and complex. Scott does explain it in detail but feels embarrassed doing so. Scott's summary is:

The quantum computer is simply asked to apply a random (but known) sequence of quantum operations—not because we intrinsically care about the result, but because we’re trying to prove that it can beat a classical computer at some well-defined task.

Google performed this task in 200 seconds and it would have taken the world's fastest supercomputer, Summit, 100,000 years. The reason this is so significant is that after billions of dollars and decades of research, this is the first time that a quantum computer has solved anything faster than you could solve it on a server, and probably on your smartphone.

Google's quantum computer has 54 qubits (around the same number as those at IBM, Intel, and probably others). A qubit can be held for a time in a superposed state where it represents both 0 and 1.

This is not something that means Google can break all the codes, or solve the traveling salesman problem, or anything like that. Scott likens it to the flight of the Wright Flyer by the Wright Brothers. It was a significant first step, but didn't mean that commercial jet aircraft were imminent, or even that you could fly ten miles. Indeed, if you were skeptical that commercial aircraft service would ever be possible, the Wright Flyer was not going to change your mind, although, as Scott points out, it shouldn't reassure you. "It is a proof of concept, but you need a proof of concept before you can do useful things."

The picture at the start of this post is not Google's quantum computer, which I have never seen, but IBM's. I took this photo since they had brought it along to ES Design West in July. It is just the internals since in operation the entire beautiful structure is immersed in liquid helium to get it as close to absolute zero as possible. To the right is an earlier version of the IBM quantum computer that I photographed when they brought it along to CES last year (2018).

Encryption

One worry about quantum supremacy is that it will break internet encryption. You may know that the public key encryption that is used for the key exchange when setting up an https: connection depends on the difficulty of factorizing a very large number into two large primes (think hundreds of digits). This is actually something that complexity theorists have never managed to prove is fundamentally hard, even for conventional computers. Google's achievement is nowhere near doing this, and cryptographers have already come up with encryption schemes that are not vulnerable to attack by quantum computers.

For more about this, see Wired's take Google’s ‘Quantum Supremacy’ Isn’t the End of Encryption.

Dario Gil, IBM’s director of research, was quoted in the Wired piece, and is worried that the term "supremacy" overhypes the achievement:

We need to build machines that have more practical value, and that is not now or next year, It’s going to take some time.

As it happens, Dario gave one of the keynotes at last year's DAC, which covered quantum computing among other things. You can read my post about that in DAC Tuesday: IBM's AI, Jay's Wall Street View, Lip-Bu's Chat, Monster Chips.

Hurry Up and Wait

Now we all have to wait for the official publication of Google's paper, and the more considered response once all the details have been announced.

But as a takeaway, let me give you the quote that Scott has in the title banner to his blog:

If you only take just one piece of information away from this blog, it is that quantum computers would not solve hard search problems instantaneously by simply trying all the solutions at once.

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