  The future of quantum information processing hinges on chip-scale
nanophotonics, specifically cavity QED and waveguide QED. One of the foremost
processes underpinning quantum photonic technologies is the phenomenon of Rabi
oscillations, which manifests when a qubit is irradiated by an intense laser
source. Departing from the conventional semiclassical framework, we expound on
the more general, quantum-theoretic case where the optical excitation takes the
form of a multiphoton Fock state, and the qubit couples to a continuum of
radiation modes. By employing the real-space formalism, we analytically explore
the scattering dynamics of the photonic Fock state as it interfaces with a
two-level emitter. The resulting amplitude for atomic excitation features a
linear superposition of various independent scattering events that are
triggered by the potential of sequential photon absorptions and emissions. The
lowest-order excitation event, initiated by the stochastic scattering of one of
the several photons, aptly characterizes the dynamics in a weak-field
environment. This is complemented by a multitude of higher-order scattering
events ensuing from repeated atom-photon interactions. The temporal evolution
of the qubit excitation in our configuration closely mirrors the semiclassical
predictions, particularly in the strong-pumping limit where Rabi oscillations
unfold. Notably, this compatibility with the semiclassical paradigm applies
both to the weak-driving and large-detuning limits. Our analysis, therefore,
extends the existing results on quantum Rabi oscillations pertinent to
single-mode cavity QED, to the multimode, waveguide-QED configurations wherein
flying photons are the information carriers. Finally, we explore the scattering
dynamics of pulsed wave packets, highlighting the potential to substantially
enhance excitation efficiency, even in scenarios involving just a few photons.
