  We present, for the first time, the quantum mechanical description of
light-matter interaction in the presence of optical cavities that are
characterized by radiative losses. Unique to radiative losses is the unitary
evolution and their full preservation of the coherence, in stark contrast to
the usually considered dissipative losses. We elucidate the reduction of exact
quantum electrodynamic equations to a form similar to the familiar
Jaynes-Cummings model through the introduction and study of a new class of
noise operators. The dynamics of this henceforth inherently dissipative model
are then presented by formulating the resulting equations of motion.
Furthermore, an input- output formalism is established, which provides a direct
connection to the dynamics of output states accessible with detectors. The
application-oriented cases of coherent and pulsed laser pumping are discussed
as inputs. Finally the single-photon dynamics in an optical cavity with
significant radiative loss - whose importance has to be contextualized in view
of the prospects of light-matter interaction applications - are reviewed
according to the proposed model. The formulation is kept as general as possible
to emphasise the universal applicability to different implementations of
quantum optical systems but from our own background we have an application in
mind in the context of nanooptics.

Quantum Physics;Optics