  In contrast to the free-space evolution of an atom governed by a multi-mode
interaction with the surrounding electromagnetic vacuum, the evolution of a
cavity-QED system can be characterized by just three parameters, (i)
atom-cavity coupling strength g, (ii) cavity relaxation rate \kappa, and (iii)
atomic decay rate into the non-cavity modes \gamma. In the case of an atom
inserted into a planar resonator with an input beam coupled from the outside,
it has been shown by Koshino [Phys. Rev. A 73, 053814 (2006)] that these three
parameters are determined not only by the atom and cavity characteristics, but
also by the spatial distribution of the input pulse. By an ab-initio treatment,
we generalize the framework of Koshino and determine the cavity-QED parameters
of a coupled system of atom, planar (leaky) resonator, and input single-photon
pulse as functions of the lateral profile of the pulse and the length of
resonator. We confirm that the atomic decay rate can be suppressed by tailoring
appropriately the lateral profile of the pulse. Such an active suppression of
atomic decay opens an attractive route towards an efficient quantum memory for
long-term storage of an atomic qubit inside a planar resonator.
