  We propose and analyze an all-magnetic scheme to perform a Young's double
slit experiment with a micron-sized superconducting sphere of mass $\gtrsim
{10}^{13}$ amu. We show that its center of mass could be prepared in a spatial
quantum superposition state with an extent of the order of half a micrometer.
The scheme is based on magnetically levitating the sphere above a
superconducting chip and letting it skate through a static magnetic potential
landscape where it interacts for short intervals with quantum circuits. In this
way, a protocol for fast quantum interferometry using quantum magnetomechanics
is passively implemented. Such a table-top earth-based quantum experiment would
operate in a parameter regime where gravitational energy scales become
relevant. In particular, we show that the faint parameter-free
gravitationally-induced decoherence collapse model, proposed by Di\'osi and
Penrose, could be unambiguously falsified.
