Nuclear spin manipulation in semiconductor nanostructures

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.