Defect centers in diamond has outstanding properties, including long coherence times and the presence of a nuclear spin bath, which make them highly promising for quantum applications. However, the technology for large-scale integration of defect centers is still in its early stages. There are various methods for the integration of diamond centers for quantum applications. Here we focus on the hybrid integration of diamond nanophotonic structures in three aspects: 1) adiabatic coupler design, 2) pick-and-place integration of diamond chiplets with silicon nitride (SiN) photonic platform, and 3) preparation of a diamond membrane for nanofabrication. An adiabatic coupler has been designed for an existing diamond chiplet. The optimal performance has been obtained at 12 μm taper length and 120 nm tip width with an insertion loss of 0.16dB, and coupling efficiency of 78.2%. It has also been demonstrated that much better performance could be obtained by reducing the diamond waveguide thickness from 485 nm to 200 nm, giving an insertion loss of 0.094dB and a coupling efficiency of 97.2%. The optimal taper lengths in this case have been determined as 12 μm for the SiN waveguide and 8 μm for the diamond waveguide. The effect of surface treatment on the pick-and-place transfer has been investigated as well. The time dependence of the contact angle of various surface treatments applied on the SiN surface has been characterized. It has been found that the optimal pick-and-place condition can be obtained with HMDS treatment at a contact angle range of 20∘ −30∘ measured by water, corresponding to a time between 1 and 2 hours after the treatment. One issue found in pick-and-place experiments is the roughness of the diamond nanophotonic chiplet bottom surface. Etching of diamond on insulator (DOI) substrates has been performed for two kinds of diamond samples. It is found that the minimum surface roughness achievable by Ar/Cl2 + Ar/O2 etching is limited by the initial surface quality. The average surface roughness was lowered from 5.71 nm to 1.19 nm using a higher-quality diamond.

The quantum diamond microscope (QDM) is a device that uses nitrogen-vacancy (NV) color centers in diamond to detect magnetic fields using a technique called optically detected magnetic resonance (ODMR). NV centers are suitable for biological measurements because they can operate at room temperature and diamond is bio-compatible. This thesis works towards integrating this technology in a compact portable quantum bio-sensor, for which a chip with single photon detectors is a promising integration platform. Before this thesis started, a CMOS chip had been fabricated with single photon avalanche diodes (SPAD) on it including circuitry for digital communication.
During this thesis, first, software was improved for an existing confocal ODMR setup, adding all necessary features for 2D scanning routines. Then, a new widefield setup was designed and established for testing the CMOS SPADs. Afterwards, the SPADs were electrically characterized and optically tested, the latter by using the widefield setup. The SPADs dit not function correctly and thus could only be partially characterized, leading to the CMOS design needing to be checked for errors. Finally, an attempt at bio-sensing was made. A sample was prepared by cultivating human embryonic kidney (HEK) cells on diamond, submersed in a 40 $\mu$g/mL solution of magnetic nanoparticles (MNP). During incubation the cells absorbed the MNPs, making them responsive to magnetism. This diamond has been scanned with the confocal setup while applying an external magnetic field of 1.07 mT. No HEK cells were found this way, even though the photo-luminescence intensity map hints at their presence within the scanning area, indicating that the external magnetic field and/or the concentration of the MNPs may be too low. More research is needed to confirm this.

To realize large-scale, optically accessible diamond-based spin quantum systems, heterogeneous integration is essential. This involves interconnecting and manipulating defect spin qubits in diamond photonic structures via intricate photonic components and circuits fabricated from materials like silicon nitride (SiN). This thesis develops and automates a characterisation setup for photonic components operating within the visible spectrum, suitable for characterising photonic components designed to implement and integrate in diamond spin quantum systems. The main goal being achieving a transmission efficiency of more than 0.2% for the provided silicon nitride waveguides. The setup is capable of measuring power and spectral response with high precision, achieving transmission loss measurements up to 3 dB/cm, limited by current waveguide/photonic component performance, and a positional accuracy of less than 100 nm. Using silicon nitride waveguides coupled with grating couplers, transmission loss measurements were obtained that closely matched previous results, validating the setup’s accuracy. To further validate the setup, a transmission efficiency of up to 3.2% was achieved for the silicon nitride waveguides, which is more than 10 times higher than results from a comparable setup. Automated measurements show below a minute measurement time per device, enabling efficient and repeatable testing. Furthermore, the Pick and Place diamond waveguide showed a transmission of 1.7 μW with an input power of 2.75 mW. This was a first in our research group and validates the performance of the characterisation setup as well. This automated setup thus provides a scalable solution for rapid photonic component evaluation, addressing integration challenges in diamond-based quantum architectures by improving measurement throughput and coupling efficiency.