Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Because of their unique coherence properties, Bose-Einstein condensates are ideal sources for an atom interferometer in extended free fall. In this Letter we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far field of a double slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.

Albert Einstein's insight that it is impossible to distinguish a local experiment in a "freely falling elevator" from one in free space led to the development of the theory of general relativity. The wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter.

Space offers virtually unlimited free-fall in gravity. Bose-Einstein condensation (BEC) enables ineffable low kinetic energies corresponding to pico-or even femtokelvins. The combination of both features makes atom interferometers with unprecedented sensitivity for inertial forces possible and opens a new era for quantum gas experiments 1, 2 . On January 23, 2017, we created Bose-Einstein condensates in space on the sounding rocket mission MAIUS-1 and conducted 110 experiments central to matter-wave interferometry. In particular, we have explored laser cooling and trapping in the presence of large accelerations as experienced during launch, and have studied the evolution, manipulation and interferometry employing Bragg scattering of BECs during the six-minute space flight. In this letter, we focus on the phase transition and the collective dynamics of BECs, whose impact is magnified by the extended free-fall time. Our experiments demonstrate a high reproducibility of the manipulation of BECs on the atom chip reflecting the exquisite control features and the robustness of our experiment. These properties are crucial to novel protocols for creating quantum matter with designed collective excitations at the lowest kinetic energy scales close to femtokelvins 3 .Quantum systems, such as matter-waves in the presence of a gravitational field 4 , shine new light on our understanding of both, general relativity 5 and quantum mechanics. Since the sensitivity for measuring inertial forces with matter-wave interferometers is proportional to the square of the time the atoms spend in the interferometer 6 , an extended free-fall promises an enormous enhancement in performance 1, 7 . In this context, Bose-Einstein condensates 8, 9 herald a shift in paradigm because they allow us to perform interferometry over macroscopic timescales on the order of tens of seconds. In addition, the extreme coherence length of delta-kick collimated BECs 10-12 , equivalent to temperatures as low as pico-or even femtokelvins, is mandatory to combine precision with accuracy 1 .Despite the generation and manipulation of this state of matter being delicate, we have successfully demonstrated key methods of atom optics in microgravity on board a sounding rocket. Our experimental apparatus 13-15 depicted in Fig. 1 is equipped with a multilayer atom chip 16-18 and achieved an, even for terrestrial experiments, high BEC flux 19 . The latter made it possible to perform a large number of experiments during the space flight, exemplified here by images of the first man-made space BEC (Fig. 1e) and Bragg scattering of a BEC (Fig. 1f). Figure 2 summarises the experiments of the MAIUS-1 mission performed in space, as well as during the launch of the rocket. They are instrumental for NASA's Cold Atom Laboratory 2 (CAL) on the International Space Station (ISS) and for the NASA-DLR multi-user facility Bose-Einstein Condensate and Cold Atom Laboratory (BECCAL), which is presently in the planning phase 20 .In this letter, we report on BEC experiments with Rubidium-87 a...

The theory of general relativity describes macroscopic phenomena driven by the influence of gravity while quantum mechanics brilliantly accounts for microscopic effects. Despite their tremendous individual success, a complete unification of fundamental interactions is missing and remains one of the most challenging and important quests in modern theoretical physics. The STE-QUEST satellite mission, proposed as a medium-size mission within the Cosmic Vision program of the European Space Agency (ESA), aims for testing general relativity with high precision in two experiments by performing a measurement of the gravitational redshift of the Sun and the Moon by comparing terrestrial clocks, and by performing a test of the Universality of Free Fall of matter waves in the gravitational field of Earth comparing the trajectory of two Bose-Einstein condensates of 85 Rb and 87 Rb. The two ultracold atom clouds are monitored very precisely thanks to techniques of atom interferometry. This allows to reach down to an uncertainty in the Eötvös parameter of at least 2 · 10 −15 . In this paper, we report about the results of the phase A mission study of the atom interferometer instrument covering the description of the main payload elements, the atomic source concept, and the systematic error sources.