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HL: Fachverband Halbleiterphysik

HL 70: Quantum Dots and Wires: Theory

HL 70.5: Vortrag

Donnerstag, 17. März 2011, 11:15–11:30, POT 151

Theory of exciton fine structure in cubic semiconductor quantum dots — •Erik Welander and Guido Burkard — Department of Physics, University of Konstanz, Konstanz, Germany

We theoretically investigate the radiative recombination of biexcitons in semiconductor quantum dots. The biexciton recombines via one out of two possible intermediate exciton states, causing two linearly photons to be emitted, | X ⟩| Y ⟩ or | Y ⟩| X ⟩. The order in which the photons are emitted depends on which exciton, | X ⟩ or | Y ⟩, mediates the recombination (which-way). If the intermediate state is energetically degenerate, a coherent superposition of the two double-photon states is possible, (| X ⟩| Y ⟩+ | Y ⟩| X ⟩)/√2. This allows the biexciton cascade recombination to produce entangled photon pairs. The geometry dependent electron-hole exchange interaction is known to remove the degeneracy of the intermediate exciton states. Since the polarization of the light then would be entangled with the photon energy, the which-path information would be available via frequency measurements and thus the creation of polarization entangled photons would no longer be possible. We develop a model for the quantum dot exciton fine-structure and its dependence on geometry. The emerging photon states are studied and explicit results are presented for a spatially asymmetric, harmonically confined GaAs quantum dot surrounded by AlAs. Moreover, we examine the possibility of restoring the degeneracy by applying external electric and/or magnetic fields.