Quantum supremacy?

This morning’s Observer column:

Something intriguing happened last week. A paper about quantum computing by a Google researcher making a startling claim appeared on a Nasa website – and then disappeared shortly afterwards. Conspiracy theorists immediately suspected that something sinister involving the National Security Agency was afoot. Spiritualists thought that it confirmed what they’ve always suspected about quantum phenomena. (It was, as one wag put it to me, a clear case of “Schrödinger’s Paper”.) Adherents of the cock-up theory of history (this columnist included) concluded that someone had just pushed the “publish” button prematurely, a suspicion apparently confirmed later by stories that the paper was intended for a major scientific journal before being published on the web.

Why was the elusive paper’s claim startling? It was because – according to the Financial Times – it asserted that a quantum computer built by Google could perform a calculation “in three minutes and 20 seconds that would take today’s most advanced classical computer … approximately 10,000 years”. As someone once said of the book of Genesis, this would be “important if true”. A more mischievous thought was: how would the researchers check that the quantum machine’s calculation was correct?

A quantum computer is one that harnesses phenomena from quantum physics, the study of the behaviour of subatomic particles, which is one of the most arcane specialisms known to humankind…

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