Bright and strain-tunable semiconductor quantum dot devices

Sammanfattning: Optically active semiconductor quantum dots have proven to be excellent single- and entangled-photon sources, with applications in quantum optics and quantum photonics. These sources are considered crucial in the development of future photonic quantum technology, such as quantum communication, quantum computation and quantum metrology. In future quantum networks, they allow to share quantum information through optical fiber links and implement secure communication protocols based on quantum key distribution.However, there are several challenges when developing quantum dot devices in order to unlock the full potential of these quantum emitters. The ideal quantum dot source efficiently generates triggered single- and entangled-photons on-demand. It provides further high collection-efficiency, low multi-photon probability, near-unity indistinguishability and high entanglement fidelity. Finally, it also offers compatibility with other systems by providing photons with the desired spectral properties and enabling efficient photon coupling.In this thesis the development and fabrication of bright and strain-tunable quantum dot devices for single- and entangled-photon generation has been studied. It covers highly-symmetric GaAs quantum dots emitting in the near-infrared, InAs quantum dots generating photons in the telecom C-band and InAsP quantum dots embedded in InP nanowires enabling deterministic integration into photonic circuits. The main aspects of operating these quantum dots in cryogenic micro-photoluminescence experiments are described, with focus on enhancing the collection efficiency using solid immersion lenses. For strain-tunability, the focus lies on the fabrication of piezoelectric actuators as substrates for the integration of quantum dot samples by polymer-based bonding. Finally, this thesis describes the simulation, fabrication and measurement of a novel device featuring quantum dots embedded in broad-band parabolic mirror microcavities for enhanced light collection.Experimental results obtained with a variety of quantum dot devices are included: GaAs quantum dot devices featuring solid immersion lenses demonstrate record-low multi-photon probability and near-unity photon indistinguishability. Piezoelectric strain-tunable devices with InAs quantum dots emitting in the telecom C-band allow for on-demand generation of single- and entangled-photons with tunable quantum dot emission properties and high entanglement fidelity. Piezoelectric strain-tuning actuators enable further the realization of reconfigurable quantum photonic circuits featuring waveguide-integrated InAsP/InP nanowire quantum dots with tunable emission wavelength. Finally, GaAs quantum dots in microcavities with parabolic mirror integrated on piezoelectric actuators achieve an increase in brightness by one order of magnitude over planar structures while allowing to tune the emission wavelength to the atomic transition 87Rb D1 relevant for quantum memory applications.