  A compact detector for space-time metric and curvature is highly desirable.
Here we show that quantum spatial superpositions of mesoscopic objects, of the
type which would in principle become possible with a combination of state of
the art techniques and taking into account the known sources of decoherence,
could be exploited to create such a detector. By using Stern-Gerlach (SG)
interferometry with masses much larger than atoms, where the interferometric
signal is extracted by measuring spins, we show that accelerations as low as
$5\times10^{-15}\textrm{ms}^{-2}\textrm{Hz}^{-1/2}$ or better, as well as the
frame dragging effects caused by the Earth, could be sensed. Constructing such
an apparatus to be non-symmetric would also enable the direct detection of
curvature and gravitational waves (GWs). The GW sensitivity scales differently
from the stray acceleration sensitivity, a unique feature of MIMAC. We have
identified mitigation mechanisms for the known sources of noise, namely Gravity
Gradient Noise (GGN), uncertainty principle and electro-magnetic forces. Hence
it could potentially lead to a meter sized, orientable and vibrational noise
(thermal/seismic) resilient detector of mid (ground based) and low (space
based) frequency GWs from massive binaries (the predicted regimes are similar
to those targeted by atom interferometers and LISA).
