Colloquium

  • Optical coupling and properties in a single coupled quantum dot

  • Speaker : Prof. Heedae Kim
    Affiliation : School of Physics, Northeast Normal University
    Date : October 6, 2021 4:00 PM
    Place : Zoom Conference Room: Physics Seminar 2021-1 (ID: 835 7220 3524, Password:1882)
    Contact : agatha0206@unist.ac.kr (Youn-young Hwang, Academic & Student Affairs Team)
    Host : Prof. Hyeong-Ryeol Park (nano@unist.ac.kr)
  • Abstract

  • Recently, the droplet epitaxy techniques allow us to grow laterally coupled quantum dot (CQD) structure. The vertically CQDs have been intensively investigated in terms of optical coupling and entangling states [1,2] When the interdot distance between two quantum dots is short enough (d< 10nm) to result in a wave function overlap between the two quantum dots via the tunneling effect, the optical coupling is controlled by the interdot distance and external DC electric fields along the coupling direction. However, in the case of a laterally CQD, the separation of two quantum dots is not small enough to give rise to a sufficient wave function overlap for tunneling to occur, the exciton dipole-dipole interaction can be used as an alternative method to understand long range optical coupling procedure.

    We found that the exciton dipole-dipole interaction in a single laterally CQD structure can be controlled by the linear polarization of optical excitation. As the excitation intensity is increased with the linearly polarized light parallel to the lateral coupling direction, excitons (X1 and X2) and local biexcitons (X1X1 and X2X2) show a redshift along with coupled biexciton (X1X2), while neither coupled biexcitons nor a redshift are observed when the direction of excitation beam is perpendicular to the coupling direction. The polarized dependence and power dependent redshift are attributed to the exciton Forster resonant energy transfer interaction. This interaction becomes significant with increasing the excitation parallel to the coupling direction, where redshifts, an exciton population transfer, and a coupled biexciton appear.

    References

    1. M. Bayer et al., Science 291, 451 (2001)

    2. W. Sheng et al., Phys. Rev. Lett. 88, 167401 (2002)