  Preparation of a so-called circular state in a Rydberg atom where the
projection of the electron angular momentum takes its maximum value is
challenging due to the required amount of angular momentum transfer. Currently
available protocols for circular state preparation are either accurate but slow
or fast but error-prone. Here, we show how to use quantum optimal control
theory to derive pulse shapes that realize fast and accurate circularization of
a Rydberg atom. In particular, we present a theoretical proposal for optimized
radio-frequency pulses that achieve high fidelity in the shortest possible
time, given current experimental limitations on peak amplitudes and spectral
bandwidth. We also discuss the fundamental quantum speed limit for
circularization of a Rydberg atom, when lifting these constraints.
