Microgravity is expected to be a decisive condition for the next leap in tests of fundamental physics of gravity, relativity, and theories beyond the standard model. Promising techniques for fundamental tests in the quantum domain are matter-wave sensors based on cold atoms or atom lasers, which use atoms as unperturbed microscopic test bodies for measuring inertial forces or as frequency references.
Microgravity is of high relevance for matter-wave interferometers and experiments with quantum matter, like Bose-Einstein condensates (BEC) or degenerate Fermi gases, as it permits the extension of the unperturbed free evolution of these test particles to long time-scales on the order of seconds in a low-noise environment.
In the beginning of the QUANTUS-Project in 2004, the ZARM drop-tower in Bremen was choosen as a microgravity platform, since it provides good accessibility and better quality of microgravity than other ground based platforms. At the drop tower, an experiment capsule can either be dropped 110m inside an evacuated vacuum-tube to generate 4.72s of microgravity time or launched in a piston-catapult, to almost double the microgravity time to 9.3s. The project, however, aims at space bound microgravity platforms like sounding rockets, ISS-experiments and satellites. In QUANTUS, the technology and the physical understanding of such high complex experimental apparatuses is being developed and preliminary studies are performed to be ready for the even more complex space applications.
The (fundamental) physics goal of the project is to test for the univerality of free fall. Therefore, two different atomic species (Rb-87 and K-41) are cooled down to quantum-degeneracy and long-time matter-wave interferometry is performed on both species. With this setup, the gravitational acceleration on both atomic species can be measured, to test for mass-dependent differences in gravitational acceleration and herewith test for the universality of free fall. Technology developed for the drop-tower experiments were either taken one-to-one or enhanced for the use on sounding-rocket missions that led to the first human made BEC in space in January 2017.
Current activities in QUANTUS are dealing with the reduction of the already slow expansion of the BEC to velocities comparable to temperatures of around 50pK. This step is crucial to expand the free evolution of the BEC during the interferometer, increasing the sensitivity of the measurement.
