  Conical intersections between electronic potential energy surfaces are
paradigmatic for the study of non-adiabatic processes in the excited states of
large molecules. However, since the corresponding dynamics occurs on a
femtosecond timescale, their investigation remains challenging and requires
ultrafast spectroscopy techniques. We demonstrate that trapped Rydberg ions are
a platform to engineer conical intersections and to simulate their ensuing
dynamics on larger length and time scales of the order of nanometers and
microseconds, respectively; all this in a highly controllable system. Here, the
shape of the potential energy surfaces and the position of the conical
intersection can be tuned thanks to the interplay between the high
polarizability and the strong dipolar exchange interactions of Rydberg ions. We
study how the presence of a conical intersection affects both the nuclear and
electronic dynamics demonstrating, in particular, how it results in the
inhibition of the nuclear motion. These effects can be monitored in real-time
via a direct spectroscopic measurement of the electronic populations in a
state-of-the-art experimental setup.
