  Reliable control of quantum information in matter-based qubits requires
precisely applied external fields, and unaccounted for spatial cross-talk of
these fields between adjacent qubits leads to loss of fidelity. We report a
CMOS foundry-produced, micro-fabricated silicon nitride (Si3N4) optical
waveguide for addressing a chain of eight, unequally-spaced trapped barium ions
with crosstalk compatible with scalable quantum information processing. The
crosstalk mitigation techniques incorporated into the chip design result in a
reduction of the measured optical field by at least 50.8(1.3) dB between
adjacent waveguide outputs near 650 nm and similar behavior for devices
designed for 493 nm and 585 nm. The waveguide outputs near 650 nm, along with a
global laser near 493 nm were used to laser-cool a chain of eight barium-138
ions, and a camera imaged the resulting fluorescence at 493 nm.
