Is That Quantum Computer for Real? There May Finally Be a Test

If Bonnie and Clyde can use only classical physics, then no matter how many “hidden variables” they share, it turns out that the best they can do is decide on a story before they get separated and then stick to it, no matter what the detective asks them, a strategy that will win the game 75 percent of the time. If Einstein had known about the Bell test, Vazirani said, “he wouldn’t have wasted 30 years of his life looking for an alternative to quantum mechanics.” He simply would have convinced someone to do the experiment. A Quantum Wrist Lock The Bell test does more than allow a physical system to prove that it is quantum, the April findings show: It gives a way for a complex quantum system to establish just what its internal state is, and what measurements it is doing. Reichardt, Unger and Vazirani showed that if Bonnie and Clyde are winning 85.4 percent of the time over many rounds of the CHSH game, then with almost perfect certainty, they must be doing it by measuring a large collection of EPR pairs — different pairs for different rounds of the game.