  Atomic interferometers have been studied as a promising device for precise
sensing of external fields. Among various configurations, a particular
configuration with a butterfly-shaped geometry has been designed to sensitively
probe field gradients. We introduce a Stern-Gerlach (SG) butterfly
interferometer by incorporating magnetic field in the conventional
butterfly-shaped configuration. Atomic trajectories of the interferometer can
be flexibly adjusted by controlling magnetic fields to increase the sensitivity
of the interferometer, while the conventional butterfly interferometer using
Raman transitions can be understood as a special case. We also show that the SG
interferometer can keep high contrast against a misalignment in position and
momentum caused by the field gradient.
