Two-laser spectroscopy and coherent manipulation of color-center spin ensembles in silicon carbide

To build quantum applications that outperform their current-day, classical counterparts (for example, unbreakable encryption, or exponentially faster computation), we require better quantum components than we now have. These carriers of quantum information (called qubits) should easily scale up to big systems, integrate well with current technology, and be affordable to boot. We explore a novel type of qubit called color center, which is a naturally occuring atom-sized qubit in certain semiconductor materials. In our material of choice, silicon carbide, hundreds of such distinct systems exist, possibly fulfilling the above criteria, each with its own pros and cons for applications. Two red threads run through this work. Firstly, the development of experimental techniques and analysis to fully characterize color centers in bulk by optical means, inside of a non-ideal, strained, inhomogeneous material (as is the natural state of such a crystal unless great care is taken when growing it). This facilitates the search for the right quantum system for the right job. Secondly we show control over the quantum state of three particular centers (two types of so-called divacancies having different symmetries, and molybdenum impurities), using only light. This work shows the strengths of the defects under investigation, and points the way to all-optical quantum applications integrated on a chip using these defects.