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We have investigated a coherent spectral change of exciton-polaritons in a ZnSe epitaxial layer. Using spectrally resolved four-wave mixing spectroscopy, we have observed the dramatically changed spectra, which exhibit an exchange of the dominant peak position between the different polariton branches. This result reflects the initial creation process of polaritons including the exciton-exciton interaction.

We have observed the excitonic wave‐packet motion through spectrally resolved four‐wave mixing measurements in a layered semiconductor GaSe, and demonstrated that the four‐wave mixing spectroscopy is a useful tool to observe the wave‐packet motion. We have found that the wave‐packet motion in a quasi‐two‐dimensional system is explained theoretically by using the configuration coordinate model, where the adiabatic potential curve is shifted due to the exciton‐phonon interaction.

Laterally aligned, unstrained GaAs/AlGaAs quantum dot molecules (QDMs) are created by droplet epitaxy, utilizing the anisotropic surface potentials of the GaAs (100) surface for the migration of Ga adatoms. Single QDM photoluminescence spectra show a doublet structure, for which effective mass approximation calculations (including the size of the QDM) suggest it originates from molecular orbital energy levels in the QDM.

We have studied the micro‐photoluminescence spectra of strain‐free GaAs/AlGaAs single quantum dots, coupled with magnetic field dependence, time‐resolved, and photon correlation measurements. The experimental behavior can be well explained by a model calculation based on the successive relaxation of multi‐excitons.

We show the coherent control of the non‐Markovian oscillation of exciton‐folded acoustic phonon scattering in GaAs multiple‐quantum wells by using four‐wave mixing measurements. The extent of non‐Markovian scattering is suppressed when the delay time between the phase‐locked pulses corresponds to half the period of the non‐Markovian oscillation.

We report the demonstration of decoherence control on excitons in a layered compound semiconductor GaSe by using successive femtosecond pulses, i.e., the multi‐wave mixing method. The intermediate pulse acts as a π‐pulse, which reverses the time evolution of non‐Markovian dynamics. By changing the pulse interval conditions, we confirmed the suppression of exciton decoherence by pulse irradiation.

Time‐resolved four‐wave mixing technique (FWM) is used to study the phonon induced dephasing of the excitons in CdTe self‐assembled quantum dots. The FWM signals show two different decay structures with fast and slow decay components, indicating a non‐Lorentzian lineshape with a zero‐phonon line and a broadband from exciton‐acoustic phonon interaction in the spectral region. The dephasing of the zero‐phonon line and the sideband components both show non‐linear characteristics with respect to temperature. The experimental data are reproduced well by a theoretical model taking into account the carrier‐acoustic phonon coupling.

The control of the dephasing of excitons was performed in GaSe by using successive three femtosecond pulses, i.e., six‐wave‐mixing. By changing the pulse interval conditions, we observed for the fist time the suppression of the dephasing of the excitons by π pulse irradiation.