Experimental test of Born's rule by inspecting third-order quantum interference on a single spin in solids

As a fundamental postulate of quantum mechanics, Born's rule assigns probabilities to the measurement outcomes of quantum systems and excludes multiorder quantum interference. Here we report an experiment on a single spin in diamond to test Born's rule by inspecting the third-order quantum interference. The ratio of the third-order quantum interference to the second order in our experiment is bounded to the scale of 1×10^-3, which provides a stringent constraint on the potential breakdown of Born's rule.