  Quantum optical input-output models are described for a class of optical
switches based on cavity quantum electrodynamics (cavity QED) with a single
multilevel atom (or comparable bound system of charges) coupled simultaneously
to several resonant field modes. A recent limit theorem for quantum stochastic
differential equations is used to show that such models converge to a simple
scattering matrix in a type of strong coupling limit that seems natural for
nanophotonic systems. Numerical integration is used to show that the behavior
of the pre-limit model approximates that of the simple scattering matrix in a
realistic regime for the physical parameters, and that it is possible in the
proposed cavity-QED configuration for low power optical signals to switch
higher-power signals at attojoule energy scales.

Quantum Physics