A single self-assembled semiconductor quantum dot in a high-finesse optical microcavity - the subject of this thesis - is an interesting quantum-mechanical system for future quantum applications.... Show moreA single self-assembled semiconductor quantum dot in a high-finesse optical microcavity - the subject of this thesis - is an interesting quantum-mechanical system for future quantum applications. For instance, this system allows trapping of an extra electron and thus can serve as a spin quantum memory, or enables high-fidelity and high-rate single-photon production. We investigate several aspects in this thesis:First, the operation and manipulation of the system is achieved using resonant laser spectroscopy. This requires filtering out of the relatively strong excitation laser, which is often done using the cross-polarization technique. This approach, however, is complicated in optical setups by spin-orbit coupling of light at the beamsplitter. We experimentally firstly explore this effect in a cryogenic optical microscope and demonstrate its importance for quantum dot based single photon sources. Next, we develop a unique setup with a cold permanent magnet and firstly realise trapping of a single electron in our particular quantum dot - cavity devices and show spin control. Then we show how true single photons from our device can be used to create novel quantum states of light. First, we investigate theoretically single photon addition to coherent laser light including several experimental imperfections - we find an universal behaviour of the photon correlation function. Finally, we demonstrate entanglement of several consecutive photons by repeatedly using Hong-Ou-Mandel quantum interference of single photons with a photon quantum memory in the form of an optical delay loop. We show that this results in quantum states of light that have Poissonian photon statistics like laser light - therefore we call them artificial coherent states - but also that they are more complicated than ordinary coherent states and contain multi-photon quantum entanglement in the form of linear cluster states, a potential resource for universal quantum computing. Show less
The lack of useful and cost-efficient group-IV direct band gap light emitters still presents the main bottleneck for complementary metal-oxide semiconductor-compatible short-distance data... Show moreThe lack of useful and cost-efficient group-IV direct band gap light emitters still presents the main bottleneck for complementary metal-oxide semiconductor-compatible short-distance data transmission, single-photon emission, and sensing based on silicon photonics. Germanium, a group-IV element like Si, is already widely used in silicon fabs. While the energy band gap of Ge is intrinsically indirect, we predict that the insertion of Ge-Ge split-[110] interstitials into crystalline Ge can open up a direct band gap transmission path. Here, we calculate from first principles the band structure and optical emission properties of Ge, Sb, and Sn split-[110] interstitials in bulk and low-dimensional Ge at different doping concentrations. Two types of electronic states provide the light-emission enhancement below the direct band gap of Ge: a hybridized L-Γ state at the Brillouin zone center and a conduction band of Δ band character that couples to a raised valence band along the Γ-X direction. Majority carrier introduced to the system through doping can enhance light emission by saturation of nonradiative paths. Ge-Sn split interstitials in Ge shift the top of the valence band towards the Γ-X direction and increase the Γ character of the L-Γ state, which results in a shift to longer emission wavelengths. Key spectral regions for datacom and sensing applications can be covered by applying quantum confinement in defect-enhanced Ge quantum dots for an emission wavelength shift from the midinfrared to the telecom regime. Show less
Steindl, P.; Maddalena Sala, E.; Alén, B.; Fuertes Marrón, D.; Bimberg, D.; Klenovský, P. 2019
We study the effects of the nonlinear piezoelectricity and the In distribution on the exciton energy, the electron-hole electric dipole moment, and the fine-structure splitting in stress-tunable In... Show moreWe study the effects of the nonlinear piezoelectricity and the In distribution on the exciton energy, the electron-hole electric dipole moment, and the fine-structure splitting in stress-tunable In(Ga)As/GaAs quantum dots integrated onto a piezoelectric actuator. In particular, we investigate in detail the contributions of various elements of the expansion of the electrical polarization in terms of externally induced elastic strain on the latter two important quantum dot properties. Based on the comparison of the effects of first- and second-order piezoelectricity we provide a simple relation to estimate the influence of applied anisotropic stress on the quantum dot dipole moment for quantum dots significantly lattice mismatched to the host crystal. Show less
In this work we study theoretically and experimentally the multi-particle structure of the so-called type-II quantum dots with spatially separated electrons and holes. Our calculations based on... Show moreIn this work we study theoretically and experimentally the multi-particle structure of the so-called type-II quantum dots with spatially separated electrons and holes. Our calculations based on customarily developed full configuration interaction ap- proach reveal that exciton complexes containing holes interacting with two or more electrons exhibit fairly large antibinding energies. This effect is found to be the hallmark of the type-II confinement. In addition, an approximate self-consistent solution of the multi-exciton problem allows us to explain two pronounced phenomena: the blue-shift of the emission with pumping and the large inhomogeneous spectral broadening, both of those eluding explanation so far. The results are confirmed by detailed intensity and polarization resolved photoluminescence measurements on a number of type-II samples. Show less
Klenovský, P.; Hemzal, D.; Steindl, P.; Zíková, M.; Křápek, V.; Humliček, J. 2015
