Constructing nano-object quantum superpositions with a Stern-Gerlach interferometer

Probing quantum mechanics and quantum aspects of general relativity, along with the sensing and constraining of classical gravity, can all be enabled by unprecedented spatial sizes of superpositions of massive objects. In this paper, we show that there is a feasible setup sourced by realizable magnetic field gradients O(10-100)T m-1 to construct a large spatial superposition of O(10-4-10-8)m for O(10-17-10-14)kg masses within a time of up to 0.1-10 seconds. The scale of superpositions is unrestricted as long as quantum coherence can be maintained for a required amount of time.