  Recent proposals for space-borne gravitational wave detectors based on atom
interferometry rely on extremely narrow single-photon transition lines as
featured by alkaline-earth metals or atomic species with similar electronic
configuration. Despite their similarity, these species differ in key parameters
such as abundance of isotopes, atomic flux, density and temperature regimes,
achievable expansion rates, density limitations set by interactions, as well as
technological and operational requirements. In this study, we compare viable
candidates for gravitational wave detection with atom interferometry, contrast
the most promising atomic species, identify the relevant technological
milestones and investigate potential source concepts towards a future
gravitational wave detector in space.
