  Cavity quantum electrodynamics has attracted substantial interest, both due
to its potential role in the field of quantum information processing and as a
testbed for basic experiments in quantum mechanics. Here, we show how cavity
quantum electrodynamics using a tunable photonic crystal nanocavity in the
strong coupling regime can be used for single quantum dot spectroscopy. From
the distinctive avoided crossings observed in the strongly coupled system we
can identify the neutral and single positively charged exciton as well as the
biexciton transitions. Moreover we are able to investigate the fine structure
of those transitions and to identify a novel cavity mediated mixing of bright
and dark exciton states, where the hyperfine interactions with lattice nuclei
presumably play a key role. These results are enabled by a deterministic
coupling scheme which allowed us to achieve unprecedented coupling strengths in
excess of 0.15 meV.
