Effects of biexcitons on exciton decoherence processes in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum dots

Exciton decoherence (dephasing) properties are examined for the effects of biexcitons in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum dots. The dephasing time of higher exciton states is measured from the linewidths of discrete exciton absorption lines by employing a high-energy-resolution microphotoluminescence excitation method in single isolated quantum dots. The excitation intensity dependence and temperature dependence of the exciton linewidth are used to consider the effects of exciton-biexciton and exciton-phonon interactions. The excitation intensity dependence reveals that the exciton-biexciton interaction contributes crucially to the exciton dephasing processes. A numerical calculation undertaken with a density-matrix method interprets this result as an enhancement of the power broadening effect due to coherent coupling between excitons and biexcitons. The temperature dependence indicates that the exciton-biexciton interaction dominates the exciton-phonon interaction below 40 K. These results provide a guideline for achieving a long-lived coherence in quantum dots, which is a key to the implementation of quantum information processing.