Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 64: Quantum Information Systems: Mostly Concepts (jointly with HL)

TT 64.8: Talk

Wednesday, March 18, 2015, 12:45–13:00, EW 202

Influence of Hyperfine Interaction on the Entanglement of Photons Generated by Biexciton Recombination — •Erik Welander, Julia Hildmann, and Guido Burkard — Department of Physics, University of Konstanz, Germany

The quantum state of the emitted light from the cascade recombination of a biexciton in a quantum dot is theoretically investigated including exciton fine structure splitting (FSS) and electron-nuclear spin hyperfine interactions. In an ideal situation, the emitted photons are entangled in polarization making the biexciton recombination process a candidate source of entangled photons necessary for the growing field of quantum communication and computation. The coherence of the exciton states in real quantum dots is affected by a finite FSS and the hyperfine interactions via the effective magnetic field known as the Overhauser field. We investigate the influence of both sources of decoherence and find that the FSS combined with a stochastic exciton lifetime is responsible for the main loss of entanglement. Furthermore, we examine the possibility of reducing the decoherence from the Overhauser field by partially polarizing the nuclear spins and applying an external magnetic field. We find that an increase in entanglement depends on the degree as well as the direction of nuclear spin polarization.