Deployment of a Binary Atomic Species Superfluid in Space

The legacy of experimentally testing the universality of free fall (UFF), held by Einstein to be at the core of his gravitational theory, reaches back to the Renaissance and continues today. In modern theories, the foundations of gravity may yet yield to those of quantum mechanics, driving a contemporary hunt for small UFF violations on Earth and in space. Cutting-edge examples include a classical experiment by the MICROSCOPE satellite mission testing down to an unprecedented $10^{-15}$ level, and ground-based tests using quantum superposition within an atom interferometer. Owing to the fundamental differences in classical and quantum motion, combining these two research paths by deploying spaceborne quantum tests masses is a long-standing goal that has led to a variety of proposed missions. Utilizing upgraded capabilities of the multi-user Cold Atom Lab instrument within the International Space Station, we report the first simultaneous production of potassium ($^{41}$K) and rubidium ($^{87}$Rb) Bose-Einstein Condensates (BECs) in space, and the creation of ultracold rubidium and potassium ($^{39}$K) mixtures. We have achieved sequential interferometry of rubidium and potassium, and the first spaceborne demonstration of simultaneous interferometry with both species. Accessing resonant interactions among these quantum mixtures will allow scientists to explore few-body physics, quantum chemistry, and fundamental physics in novel energy regimes without the perturbing force of gravity. This work is a key pathfinder for prospective quantum tests of the universality of free fall in space.