  The development of alternative platforms for computing has been a
longstanding goal for physics, and represents a particularly pressing concern
as conventional transistors approach the limit of miniaturization. A potential
alternatice paradigm is that of reservoir computing, which leverages unknown,
but highly non-linear transformations of input-data to perform computations.
This has the advantage that many physical systems exhibit precisely the type of
non-linear input-output relationships necessary for them to function as
reservoirs. Consequently, the quantum effects which obstruct the further
development of silicon electronics become an advantage for a reservoir
computer. Here we demonstrate that even the most basic constituents of matter -
atoms - can act as a reservoir for optical computers, thanks to the phenomenon
of High Harmonic Generation (HHG). A prototype single-atom computer for
classification problems is proposed, where parameters of the classification
model are mapped to optical elements. We numerically demonstrate that this
`all-optical' computer can successfully classify data with an accuracy that is
strongly dependent on dynamical non-linearities. This may pave the way for the
development of petahertz information processing platforms.
