Ultranarrow polaritons in a semiconductor microcavity

We have achieved a record high ratio (19) of the Rabi splitting (3.6 meV) t o the polariton linewidth (190 mu eV), in a semiconductor lambda microcavit y with a single 25 nm GaAs quantum well at the antinode. The narrow polarit on lines are obtained with a special cavity design which reduces the excito n broadening due to scattering with free charges and has a very low spatial gradient of the cavity resonance energy. Since the static quantum-well dis order is very small, the polariton broadening is dominantly homogeneous. St ill, the measured linewidths close to zero detuning cannot be correctly pre dicted using the linewidth averaging model. (C) 2000 American Institute of Physics. [S0003- 6951(00)02922-3].