  The temporal dynamics of charge carriers determines the speed with which
electronics can be realized in condensed matter, and their direct manipulation
with optical fields promises electronic processing at unprecedented petahertz
frequencies, consisting in a million-fold increase from state of the art
technology. Graphene is of particular interest for the implementation of
petahertz optoelectronics due to its unique transport properties, such as high
carrier mobility with near-ballistic transport and exceptionally strong
coupling to optical fields. The back action of carriers in response to an
optical field is therefore of key importance towards applications. Here we
investigate the instantaneous response of graphene to petahertz optical fields
and elucidate the role of hot carriers on a sub-100 fs timescale. Measurements
of the nonlinear response and its dependence on interaction time and field
polarization allow us to identify the back action of hot carriers over
timescales that are commensurate with the optical field. An intuitive picture
is given for the carrier trajectories in response to the optical-field
polarization state. We note that the peculiar interplay between optical fields
and charge carriers in graphene may also apply to surface states in topological
insulators with similar Dirac cone dispersion relations.
