  Ion trap systems built upon microfabricated chips have emerged as a promising
platform for quantum computing to achieve reproducible and scalable structures.
However, photo-induced charging of materials in such chips can generate
undesired stray electric fields that disrupt the quantum state of the ion,
limiting high-fidelity quantum control essential for practical quantum
computing. While crude understanding of the phenomena has been gained
heuristically over the past years, explanations for the microscopic mechanism
of photo-generated charge carrier dynamics remains largely elusive. Here, we
present a photo-induced charging model for semiconductors, whose verification
is enabled by a systematic interaction between trapped ions and photo-induced
stray fields from exposed silicon surfaces in our chip. We use motion-sensitive
qubit transitions to directly characterize the stray field and analyze its
effect on the quantum dynamics of the trapped ion. In contrast to incoherent
errors arising from the thermal motion of the ion, coherent errors are induced
by the stray field, whose effect is significantly imprinted during the quantum
control of the ion. These errors are investigated in depth and methods to
mitigate them are discussed. Finally, we extend the implications of our study
to other photo-induced charging mechanisms prevalent in ion traps.
