Characterization of Fast Ion Transport via Position-Dependent Optical Deshelving

Ion transport is an essential operation within some models of quantum computing, where fast ion transport with minimal motional excitation is necessary for efficient, high-fidelity operations. We demonstrate fast linear transport of Ca⁺ in a surface-electrode ion trap, measuring average ion velocities up to 219 m/s over a distance of 120 µm by characterizing the ion’s trajectory via a position-dependent optical deshelving technique. Here we prepare the ion in the D_5/2 level before transport and then partially repump it to S_1/2 via a short (100 ns) 854 nm laser pulse at a later time. The Gaussian intensity profile of the laser beam leads to a position-dependent repump probability which we measure and invert to determine the ion’s position at a given instant. We also characterize the axial normal mode excitation using a Fast Fourier Transform analysis of the blue sideband Rabi spectroscopy to obtain the thermal and coherently excited portions of the ion’s motional state. We remove the coherently excited portion by applying a resonant radiofrequency pulse with appropriate amplitude, frequency, and phase to achieve a final axial mode occupation n<1.  This work was done in collaboration with Los Alamos National Laboratory.