  We report on the observation of the strong coupling regime between a single
GaAs quantum dot and a microdisk optical mode. Photoluminescence is performed
at various temperatures to tune the quantum dot exciton with respect to the
optical mode. At resonance, we observe an anticrossing, signature of the strong
coupling regime with a well resolved doublet. The Vacuum Rabi splitting amounts
to 400 &#956;eV and is twice as large as the individual linewidths.
