We show the coherent control of dephasing process of exciton polarization due to heavy hole-heavy hole and heavy hole-light hole scatterings in a GaAs single quantum well. The memory time of the exction scattering is estimated as 0.47 ps.
We report the non-Markovian nature of heavy hole-heavy hole and heavy hole-light hole exciton scattering in a GaAs single quantum well. The homogeneous width depends on the exciton population, which is controlled by the delay time of phase-locked pulses. This effect is explained on the basis of excitation-induced dephasing in Markovian approximation. For short times, the homogeneous width decreases and deviates from the Markovian behavior, due to the non-Markovian behavior of the exciton-exciton scattering. We analyze the homogeneous width by using a weakly interacting boson model including the non-Markovian effect. The correlation time of the exciton-exciton scattering is estimated as 0.43 ps.
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 depends on the delay time ${t}_{{1}^{\ensuremath{'}}1}$ between the phase-locked pulses. The phenomenological dephasing time in the long-time (Markovian) region does not depend on the scattering. The dephasing process is suppressed when ${t}_{{1}^{\ensuremath{'}}1}$ corresponds to half the period of the non-Markovian oscillation. The dephasing suppression is the result of a fifth-order nonlinear optical effect (a six-wave mixing process).
Based on fully microscopic kinetic spin Bloch equation approach, we show the non-Markovian effect in spin dephasing of heavy holes in p-type GaAs quantum wells. The non-Markovian effect manifests itself in spin dephasing when the mean spin precession time is shorter than the momentum relaxation time. The spin dephasing becomes slower when the non-Markovian effect is important. Moreover, quantum spin beats due to the memory effect of the non-Markovian hole--longitudinal-optical phonon scattering are predicted.
We describe a novel three-pulse degenerate four-wave mixing configuration that permits the direct observation of the coherence between the σ+ and the σ− exciton states in a GaAs quantum well excited in a two-photon process. It is found that the phase coherence between the two single heavy-hole exciton states decays with a time constant that is considerably longer than the dephasing time of the coherence between these states and the ground state (interband coherence). All the experimental data are well described by numerical solutions of the optical Bloch equations for a phenomenological multilevel model.
We present an experimental and theoretical study of the dephasing of heavy-hole excitons in a 70-\AA{} GaAs/Alx${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As multiple-quantum-well stucture. We measure the time-integrated three-pulse four-wave-mixing signal of heavy-hole excitons in the quantum-well sample. We model the third-order nonlinear optical response incorporating the effects of a stochastic modulation of the transition frequency. We find that the dephasing of the nonlinear polarization is mainly the result of a spectral-migration process of the excitons and, to a lesser extent, due to a homogeneous dephasing process. The time dependence of the four-wave-mixing signal is very well described by theory if the spectral-migration process is assumed to be energy dependent.
We investigate interband coherences as well as coherences between ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}}$ exciton states in a 10 nm thick ZnSe/ZnMgSe single quantum well by spectrally resolved three-pulse degenerate four-wave mixing using circularly polarized 100 fs pulses. Polarization and intensity dependent measurements are performed to identify the coherent processes responsible for the nonlinear signal into the ${\mathbf{k}}_{3}+{\mathbf{k}}_{2}\ensuremath{-}{\mathbf{k}}_{1}$ direction and to study the influence of Coulomb scattering on the dephasing rates. The experiments reveal nearly equal zero-density dephasing rates for coherences between ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}}$ heavy- and/or light-hole exciton states as compared to the dephasing rate of the interband coherence between these states and the ground state. The measurements also demonstrate that exciton--exciton scattering destroys the phase coherence between heavy- and light-hole excitons about three times more effectively than the coherence between ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}}$ heavy-hole excitons. The characteristic features of the experimental results are explained and reproduced by numerical calculations of the optical Bloch equations for a ten-level model including excitation induced dephasing.