We experimentally demonstrate atom interferometry using the transverse phase profile of an optical mode. As proof of principle, we use the helical phase windings of hypergeometric-Gaussian beams for Ramsey interferometry with ensembles of ballistically expanding cold ${}^{87}\mathrm{Rb}\mathrm{atoms}$, and we show that the interferometer can measure rotations induced by a motor with a sensitivity that scales linearly with orbital angular momentum and interferometer time. We characterize the thermal decoherence of the interferometer, deriving and experimentally confirming a closed-form expression for the spatially varying interferometer visibility arising near the singularity of the helical phase winding, motivating the use of condensed atoms in ring-shaped traps.

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• Atom interferometry
• Atom optics
• Optical vortices
• Spatial profiles of optical beams
• Structured light