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Spin and Photon Coherence and Entanglement in Semiconductor Quantum Dots

Spin and Photon Coherence and Entanglement in Semiconductor Quantum Dots

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WELANDER, Erik, 2014. Spin and Photon Coherence and Entanglement in Semiconductor Quantum Dots [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Welander2014Photo-28880, title={Spin and Photon Coherence and Entanglement in Semiconductor Quantum Dots}, year={2014}, author={Welander, Erik}, address={Konstanz}, school={Universität Konstanz} }

Welander, Erik eng Welander, Erik The aim of this thesis is to theoretically investigate two possible applications of semiconductor quantum dots for the growing field of quantum information and communication. The first one is the generation of entangled photons, which can be created by the radiative recombination of a quantum dot biexciton. This non-classical state of light is for instance used for teleportation of quantum information over distance. Although other methods of creating entangled photons exist, they suffer from problems such as inefficiency and unreliability, and an alternative which can produce an entangled photon pair on-demand within a given time interval would be most welcome. The second application is the implementation of a quantum bit using the intrinsic angular momentum of a single electron confined to a quantum dot. The quantum bit is the basic element of any quantum computer and is used to store quantum information.<br /><br /><br />The work is divided into four main parts. We begin with an introduction which contains a short description about entanglement and quantum information followed by a brief review about the electron structure of semiconductors. This review aims to provide knowledge about some key methods and results from the semiconductor physics, which we will need in the following chapters.<br />In the second part we will turn our attention to the generation of entangled light by the recombination of semiconductor biexcitons, which are composed of two excitons. We will discover that the excitons show an energy structure which requires extending the semiconductor theory from the introduction to be able to properly describe the observed effects. Once the exciton energy structure is known, we will examine a method to improve the quality of the emitted light with respect to entanglement.<br /><br /><br />The third part considers effects from interactions between nuclear and electron spins. Focusing on storing one quantum bit using a single electron spin, we investigate the possible loss of information caused by interaction with the nuclear spins. We find that the temporal fluctuations of the nuclear spins give rise to an upper limit on the electron coherence time, during which quantum information can be accurately stored. We also investigate possible techniques to reduce the fluctuations and prolong the coherence time.<br /><br /><br />In the fourth part we combine knowledge about the nuclear spins with the biexciton recombination process to investigate what effect exciton-nuclear spin interaction has on the entangled light. We find that the interaction with nuclear spins degrades the entanglement of the emitted light. To restore the quality of the entanglement, we investigate the effect of polarizing the nuclear spins and find that this can improve the entanglement. terms-of-use 2014-09-02T11:16:02Z 2014-09-02T11:16:02Z 2014 Spin and Photon Coherence and Entanglement in Semiconductor Quantum Dots

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