  We demonstrate highly efficient switching of optical signals between two
optical fibers controlled by a single atom. The key element of our experiment
is a whispering-gallery mode bottle microresonator, which is coupled to a
single atom and interfaced by two tapered fiber couplers. Even in the presence
of the coupling fibers, the atom--resonator system reaches the strong coupling
regime of cavity quantum electrodynamics (CQED), leading to a vacuum Rabi
splitting in the excitation spectrum. We systematically investigate the
switching efficiency of our system, i.e., the probability that the CQED
fiber-optical switch redirects the light into the desired output. We obtain a
large redirection efficiency reaching a raw fidelity of more than 60% without
post-selection.
