Quantum Test of the Universality of Free Fall

The universality of free fall (UFF) emerges [1] from theequality of the inertial and the gravitational mass, whichHeinrich Hertz [2] already in 1884 called a ”wonderfulmystery”. In 1915 Albert Einstein made this postulateinto one of the cornerstones of general relativity. Al-though UFF has been verified in numerous tests [3, 4] to-day different scenarios reconciling general relativity andquantum mechanics allow a violation of the UFF. Forthis reason more precise tests are presently pursued [5–7] and new measurement techniques are developed. Oneintriguing approach consists of comparing the accelera-tions of different quantum objects to a high precision. Inthis Letter, we report the first quantum test of the UFFwith matter waves of two different atomic species.We simultaneously compare the free-fall accelerationsg