  Access to the neutron orbital degree of freedom has been enabled by the
recent actualization of methods to prepare and characterize neutron helical
waves carrying orbital angular momentum (OAM) at small-angle neutron scattering
(SANS) facilities. This provides new avenues of exploration in fundamental
science experiments as well as in material characterization applications.
However, it remains a challenge to recover phase profiles from SANS
measurements. We introduce and demonstrate a novel neutron interferometry
technique for extracting phase information that is typically lost in SANS
measurements. An array of reference beams, with complementary structured phase
profiles, are put into a coherent superposition with the array of object beams,
thereby manifesting the phase information in the far-field intensity profile.
We demonstrate this by resolving petal-structure signatures of helical wave
interference for the first time: an implementation of the long-sought recovery
of phase information from small-angle scattering measurements.
