Manipulating fine structure splitting and exciton energy in semiconductor quantum dots
Ranber Singh (Max-Planck-Institute für Festkörperforschung, Stuttgart)

Semiconductor quantum dots (QDs) are being investigated for the generation and manipula- tion of single photons and entangled photon pairs. A QD placed inside an optical microcavity has enhanced spontaneous emission of photons through the Purcell effect and can be used as an efficient single photon source. In an idealized QD with degenerate intermediate exciton states the polarization of a photon stemming from, biexciton (|XX> ) → exciton (|X> ), is entangled with a photon stemming from, exciton (|X> ) → ground state (|0> ). However, in real self-assembled semiconductor QDs grown along the [001] crystallogroghic direction the existence of non-vanishing energetic difference between the intermediate exciton states (“so-called” fine structure splitting (FSS)) destroys the polarization entanglement between the photons produced in biexciton cascade process. Thus, to use the QDs as a source of on demand single photons and entangled photon pairs, we need to manipulate the QD’s photon energy and reduce FSS to zero. In this talk I will address these issues of tuning the QD’s photon energy and FSS by applying external perturbations and growing the QDs along high symmetry growth directions.