A better understanding of gravity is today one of the most important issues in fundamental physics. We lack a joint theory for gravity and quantum mechanics. Promising candidates for resolving this issue predict new forces, which might lead to a modification of the equivalence principle. The principle of equivalence states that the gravitational mass equals the inertial mass and that bodies of different mass and composition should display an equal rate of free fall.

One of the most puzzling features of matter is its wave nature. The propagation of matter waves in gravity is at the heart of both gravity and quantum mechanics. The Task Group “Quantum Test of the Equivalence Principle” develops tools for tailoring matter waves for precision experiments. The tools enable testing of the universal propagation of matter waves. Matter waves are very efficiently formed from different isotopes of potassium and rubidium. The resultant wave propagation is compared using precision interferometry to an accuracy of a few billionths of the acceleration due to gravity.

This will be the first dedicated experiment to compare the propagation of matter waves using state-of-the-art techniques. The sensitivity of these experiments is greatly enhanced by the extended time of free fall of these quantum objects. The scientists are therefore aiming at an even more challenging approach to do such an experiment to be carried out in a in drop tower or even in space. A first step is the demonstration of Bose-Einstein condensation in microgravity at the 146 meter high drop tower in Bremen.