Observing odd numbers of polaritons in pillar microcavities

The polarisation dynamics of a GaAs/AlGaAs micropillar in the non-linear regime under non-resonant excitation is studied.The polarisation of photoluminescence from a microcavity in the strong coupling regime is directly linked to the spin state of the polaritons when they decay, i.e. polaritons with spin-up or spin-down. This splitting leads to an oscillation in the linear polarisation of the photoluminescence. The energy splitting required producing the oscillation period that we observe corresponds to an imbalance of a single polariton.