Universiteit Leiden

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Quantum dots in microcavities: From single spins to engineered quantum states of light

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. 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.

P. Steindl
05 juli 2023
Thesis in Leiden Repository

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.

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