At the heart of the work is a differential interferometry scheme using Bose-Einstein condensed rubidium atoms. By comparing two spatially separated Mach-Zehnder interferometers, common noise sources such as laser phase noise and vibrational noise cancel out, enabling precise measurements even under the challenging vibrational conditions of the ISS. Using such interferometer sequences, the researchers were also able to infer curvatures of the magnetic field. Comparing measurements on magnetically sensitive and magnetically insensitive atomic states further allowed the team to confirm unambiguously that the measured forces are indeed of magnetic origin.

This was made possible through careful characterization of the interferometry laser beam and improved control of the atom source, which significantly extended the interaction time between the atoms and the laser beam. As a result, the experiments achieved interferometer times of up to 40.3 milliseconds, clearly surpassing previous realizations of Bose-Einstein condensate interferometers in space. The team determined the local magnetic field curvature inside the experiment's vacuum chamber to be (614.1 ± 0.3) nanotesla per millimeter squared.

Within the consortium, Professor Giese's group (opens in new tab), which is also involved in other projects funded by the German Aerospace Center, contributed to proposals for the interferometer sequences used and was involved in data anlysis collected aboard the space station.

The results are relevant for future precision measurements with quantum sensors in space: magnetic field gradients are among the leading systematic error sources in atom interferometry experiments, for instance in tests of general relativity. Since only the atoms themselves have access to the interior of the vacuum chamber, in-situ characterization performed directly in space provides important information at the exact measurement location for the design of future missions. Beyond this, the differential approach opens perspectives for multi-modal quantum sensors that could capture both magnetic fields and gravity gradients of the Earth.