Polarization-correlated three-photon emission from charged triexcitons in a single quantum dot

We demonstrate polarization-correlated three-photons emitted from a positively charged triexciton in a self-assembled GaAs quantum dot (QD). The charged triexciton consists of three electrons and four holes. Several intermediate states appear in the cascade recombination because of the exchange interaction. Spin singlet and triplet states of charged biexcitons and charged excitons are respectively identified in the photoluminescence spectra. We found that the degree of polarization correlation of the three-photons is different according to which intermediate states are used. A pathway through an excited state of a charged biexciton shows a high degree of polarization correlation, because the polarizations of these photons are dominantly determined by electron spins, which have longer lifetime than the holes. The spin relaxation times were estimated for an electron and a hole by a rate equation analysis with cross-correlation measurements.