Stephen Ornes in Quanta:
It was billed as the vindication of the quantum computer. Late last year, researchers at Google announced that a quantum machine called the D-Wave 2X had executed a task 100 million times faster than a classical computer. The claim implies that the machine can complete in one second a task that might take a classical computer three years.
It also erased one facet of the skepticism that has long faced this particular version of a quantum computer. In the past, critics of so-called “quantum annealers” made by the Canadian company D-Wave Systems have wondered if the machines make use of intrinsically quantum processes at all.
Part of the problem lies in the catch-22 of quantum computing: The quantum features only work when they’re not being observed, so observing a quantum computer to check if it’s exploiting quantum behavior will destroy the quantum behavior being checked. “It’s hard to devise a physics experiment to study something you aren’t allowed to observe,” said Catherine McGeoch, a computer scientist at D-Wave. December’s news convincingly satisfied critics that the quantum annealer really does exploit uniquely quantum effects.
But it didn’t settle a more important question: What can these computers do that classical computers can’t? The claim of a 100-million-factor speedup did not conclusively prove that the D-Wave 2X — and quantum annealers in general — will profoundly surpass the abilities of classical machines.