  Practical and useful quantum information processing (QIP) requires
significant improvements with respect to current systems, both in error rates
of basic operations and in scale. Individual trapped-ion qubits' fundamental
qualities are promising for long-term systems, but the optics involved in their
precise control are a barrier to scaling. Planar-fabricated optics integrated
within ion trap devices can make such systems simultaneously more robust and
parallelizable, as suggested by previous work with single ions. Here we use
scalable optics co-fabricated with a surface-electrode ion trap to achieve
high-fidelity multi-ion quantum logic gates, often the limiting elements in
building up the precise, large-scale entanglement essential to quantum
computation. Light is efficiently delivered to a trap chip in a cryogenic
environment via direct fibre coupling on multiple channels, eliminating the
need for beam alignment into vacuum systems and cryostats and lending
robustness to vibrations and beam pointing drifts. This allows us to perform
ground-state laser cooling of ion motion, and to implement gates generating
two-ion entangled states with fidelities $>99.3(2)\%$. This work demonstrates
hardware that reduces noise and drifts in sensitive quantum logic, and
simultaneously offers a route to practical parallelization for high-fidelity
quantum processors. Similar devices may also find applications in neutral atom
and ion-based quantum-sensing and timekeeping.
