Biexcitons or bipolaritons in a semiconductor microcavity

A well-resolved nonlinear optical transition associated with biexcitons is observed in a high-quality microcavity with a Rabi splitting exceeding the binding energy of biexcitons in the embedded quantum well. This transition is identified as an induced absorption from the lower polariton to the biexciton. The biexciton binding energy is found not to be significantly affected by the coupling with the cavity photons. In spite of the high quality of the sample, formation of a bipolariton as a bound state of two lower cavity polaritons with small in-plane wave vectors is not resolved.