A Reality Check on Quantum Computers

Companies like Rigetti are betting on making money by building quantum computers.

Whether they prove to be right or wrong, their motives aren't primarily scientific.

Or, not exactly unheard of, they aim at finding a buyer for themselves well before a time when it may become clear whether the product would really be viable or not. In those cases the product is the company itself and they don't need to have a finalized working and useful real product. Works especially well in "hype" topics where hope can more easily win against common sense (of the buyer).

> The most profound issue, however, concerns the meaning of quantum supremacy. After all, it doesn’t take qubits to solve important quantitative problems faster than any classical computer. Any carbon atom can “calculate” the solution of a very important practical problem—how does carbon behave?—simply by doing its thing.

The author [1] is trivializes the notion of computational machine. Calculating using a classical/quantum computer vs doing the experiment, differ in at least two important respects.

(1) Computers are fully programmable while experimental setups are usually specific to calculating a choice few parameters. The universality of various computational models implies exactly this: a well designed physical machine can simulate any other physical system, assuming you have the correct model of the system. A carbon-spectra calculating experimental setup does not have this universal programmability.

(2) A computer often yields the correct answer with a lot fewer resources, again assuming your model of the simulated system is correct. This is because, a well designed computation can ignore unneeded part of the model, which the experimental system must include. In fact, computers are precisely useful where we can get such an advantage, and useless where we can't. As the author points out this is not possible for some carbon atoms, and it also is not possible for medical drugs. But it is possible for a wide variety of other systems - say rockets to the moon.

[1] a Nobel prize winner, so take my words with a grain of salt.

I think he is well aware of this. The current quantum device Google build is however not much different than a sufficiently complex other physics experiment and so far they have not been able to demonstrate that it is capable of fault-tolerant error-corrected computation (which they basically won't be able to do in the foreseeable future).