We report a novel GaAs-based device in which I = 3/2 nuclear spins of 69Ga, 71Ga and 75As in a nanometer scale region
can be manipulated by all-electrical means. The device comprises a quantum point contact (QPC), a narrow conduction
channel in a GaAs quantum well defined by split gates, integrated with an additional metal strip on top for applying a
radio-frequency (RF) pulse. With the device set in a special condition characterized by the Landau-level filling factor v =
2/3, nuclear spins in the narrow region near the QPC can be selectively polarized by driving a current through the QPC.
By applying a resonant RF pulse, the polarized nuclei can be coherently manipulated, which we detect through the
electrical resistance of the QPC. Different from the conventional nuclear magnetic resonance measuring the transverse
component of the magnetization, our device measures the longitudinal component, which enables us to observe
otherwise invisible multiple quantum coherences between states with z projection of the angular momentum differing by
more than one. By appropriately tuning the length, intensity, and detuning of the RF pulse, all possible coherent
superposition between two out of the four Zeeman levels can be created for each nuclide.