  We describe the design of a surface-electrode ion trap junction, which is a
key element for large-scale ion trap arrays. A bi-objective optimization method
is used for designing the electrodes, which maintains the total
pseudo-potential curvature while minimizing the axial pseudo-potential gradient
along the ion transport path. To facilitate the laser beam delivery for
parallel operations in multiple trap zones, we implemented integrated optics on
each arm of this X-junction trap. The layout of the trap chip for commercial
foundry fabrication is presented. This work suggests routes to improving ion
trap junction performance in scalable implementations. Together with integrated
optical addressing, this contributes to modular trapped-ion quantum computing
in interconnected 2-dimensional arrays.
