Sofie Lindskov HansenSofie Lindskov Hansen

A thesis submitted  September 2017 for the degree of Doctor of Philosophy and defended November, 2017.

The PhD School of Science
Faculty of Science, Quantum Photonics Group, Niels Bohr Institute, University of Copenhagen

Academic supervisor:
Peter Lodahl

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Single-Photon Manipulation inNanophotonic Circuits

Quantum dots in photonic nanostructures has long been known to be a very powerful and versatile solid-state platform for conducting quantum optics experiments. The present PhD thesis describes experimental demonstrations of single-photon generation and subsequent manipulation all realized on a gallium arsenide platform.

This platform offers near-unity coupling between embedded single-photon emitters and a photonic mode, as well as the ability to suppress decoherence mechanisms, making it highly suited for quantum information applications. In this thesis we show how a single-photon router can be realized on a chip with embedded quantum dots. This allows for on-chip generation and manipulation of single photons. The router consists of an on-chip interferometer where the phase difference between the arms of the interferometer is controlled electrically. The response time of the device is experimentally shown to be in the sub-microsecond range.

The performance of the device is limited by the reflections from the out-coupling gratings used, and we thus developed a new type of out-coupler that reduces reflections as well as increases the coupling efficiency to the fiber. The grating design is inspired by a well-known design from silicon photonics and is adopted for quantum dot emission wavelengths. The new gratings offer a fivefold increase in efficiency compared to the gratings used previously. These results are found from simulations as well as transmission measurements and have recently been confirmed in singlephoton experiments.

Lastly, an examination of some of the possible applications of quantum dots efficiently coupled to the propagating mode of a photonic crystal waveguide is presented. Specifically, we describe how we can realize propagation-direction-dependent light-matter interactions in engineered nanostructures, and how we can utilize a well coupled quantum dot to realize giant nonlinearities at the single-photon level.

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