• blue-UV wavelengths
• circular polarization
• integrated photonics
• outcoupler
• polarization purity
• quantum computing
• trapped ion
• waveguide

One of the most ambitious goals of modern Physics and Computer Science is the realization of a universal quantum computer. Among all the implementations of quantum systems as quantum bits (qubits) that are tested and pursued, ion trapping represents one of the most promising options. This is due to the long coherence times and lifetime of the electronic states used to encode the qubit.
However, scalability is possibly the most challenging to fulfil among all DiVincenzo's criteria for quantum computation and this is not just for trapped ion-based quantum processors, but for every kind of implementation.
For this reason, a development in designing ion traps and in-chip photonics is lately strongly pursued. In fact, integrated photonics have shown early promise, but the requirements of trapped-ion systems raise numerous challenges for integrated photonics. In particular, generating pure circularly polarized fields for state preparation and readout in ion-based qubits (and to some extent for laser cooling, i.e. EIT), and developing materials capable of guiding the blue and UV wavelengths of interest are two of major challenges in this direction.

The present Thesis aims at studying a micro-metric ring resonator, that in its structural simplicity and without active tuning, is able to emit highly pure P~99.9% circularly-polarized beams, that can be integrated into next-generation ion trap designs and used for high fidelity quantum state control. Furthermore, a study on Hafnium Dioxide (HfO2), used to realize multi-layer composite together with Alumina Al2O3, as a potential low-loss high refractive index material for blue-UV waveguides is presented. The resulting material gets as low as ~2.2 dB/cm for slab mode loss and ~4.2 dB/cm for material loss keeping an effective refractive index of n~1.96 at 406 nm, maintaining high performances in the whole visible spectrum. Furthermore, the deposition approach presents the possibility for further optimization. This multi-layer nano-laminate can be suitable for high-contrast diffraction gratings and highly confining waveguides in the blue-UV.