Optical control and electron-phonon dynamics in semiconductor quantum dot structures
Prof. Dr. Tilmann Kuhn
(Westfälische Wilhelms-Universität Münster)
18.01.2012
By using optical pulses the quantum state of electrons in a semiconductor quantum dot can be manipulated to a high degree in a controlled way. This makes such structures promising candidates for many new applications in the fields of optoelectronics, spintronics and quantum information processing. Limitations in the controllability arise due to the coupling of the electrons to the environment, here in particular the coupling to the phonons. In this talk I will discuss different aspects related to the electron-phonon interaction and optical control scenarios in quantum dot structures.
In the first part I will review some of our recent results on the coupled electron-phonon dynamics quantum dot structures. The optical excitation of an exciton in the quantum dot gives rise to the creation of a lattice displacement. One part of this displacement remains in the region of the dot and forms a polaron, the other part leaves the dot region and is thus the reason for decoherence. I will discuss the role of phonons for the dephasing after an excitation by an ultrafast laser pulse as well as for the damping of Rabi oscillations in the case of a continuous excitation.
In the second part I will present recent results on the optical control of the Mn spin state in a quantum dot doped with a single Mn atom. Here the light field does not directly couple to the Mn spin. However, the Mn spin is strongly exchange-coupled to the spins of electrons and holes, which allows one to manipulate the Mn spin state via an optical manipulation of the exciton states. I will show different protocols based on suitable sequences of circularly polarized light pulses tuned either to the heavy hole exciton or the light hole exciton transition that allow one to drive the Mn spin into each of its eigenstates.