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 $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, which provides a stringent constraint on the potential breakdown of Born's rule.