According to popular science mag Nature, physicist Paul Kwiat has built a Quantum computer which uses 'counterfactual computation' which can infer an answer before it knows the question.
Apparently by using two coupled optical interferometers, nested within a third, Kwiat's team managed to counterfactually search a four-element database using Grover's quantum search algorithm, said Nature.
By placing a photon in a quantum superposition of running and not running the search algorithm, the team managed to get the answer even when the photon did not run the search algorithm.
Unfortunately the computer cannot be scaled up so that it can do anything more useful, like guessing which horse will win the Grand National or calculating the correct lottery numbers.
More here. µ
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