  Conical intersections (CI) between molecular potential energy surfaces with
non-vanishing non-adiabatic couplings generally occur in any molecule
consisting of at least three atoms. They play a fundamental role in describing
the molecular dynamics beyond the Born-Oppenheimer approximation and have been
used to understand a large variety of effects, from photofragmentation and
isomerization to more exotic applications such as exciton fission in
semiconductors. However, few studies have used the features of a CI as a tool
for coherent control. Here we demonstrate two modes of control around a conical
intersection. The first uses a continuous light field to control the population
on the two intersecting electronic states in the vicinity of a CI. The second
uses a pulsed light field to control wavepackets that are subjected to the
geometric phase shift in transit around a CI. This second technique is likely
to be useful for studying the role of nuclear dynamics in electronic coherence
phenomena.
