For decades, physicists have worked to prove the strange predictions of quantum mechanics with real experiments. As quantum computers have grown more powerful, researchers have devised increasingly sophisticated ways to test whether these machines are truly harnessing quantum effects—but every method so far has run into limits.

In new research published in Nature Communications, a team led by computer scientists Marcello Benedetti and Harry Buhrman at Quantinuum in the U.K. has proposed a new kind of test built around a simple game with a mathematically guaranteed outcome.