Caratterizzazione delle proprietà quanto-ottiche di centri stagno-vacanza in diamante

We are currently in the midst of the second quantum revolution, it will take the rules of the first quantum revolution and use them to develop new technologies,\autocite{SR} such as quantum metrology, quantum key distribution and quantum entanglement. Its start may be fixed in the 1980s when Richard Feynman realised that a quantum system was essential to simulate another quantum system. The essential building block for the development of these technologies are Single Photon Sources (SPS). During the past decade, diamond has emerged as one of the most appealing materials of study within the field of photonics, because its lattice can host different defects, named colour centres, that can be single photon sources. In 1997 the first colour centre in diamond was discovered, it was the nitrogen-vacancy (NV) defect. Since 1997, a lot of colour centres have been discovered and investigated. Nowadays, of particular interest are inversion-symmetric colour centres based on group-IV impurities (SiV, GeV, SnV, PbV) because they strongly emit into their zero-phonon lines and are insensitive to electric field noise to first order. Among group-IV colour centres, the SiV is the most studied. Despite its advantageous properties, it displays low single-photon emission rates. Therefore, the other defects are studied. The knowledge and the control of their charge state are one of the major issues. More precisely, tin-vacancy colour centres (SnV) in diamond have emerged as promising candidates for quantum emitters because of their excellent optical and spin properties including narrow-linewidth emission and long spin coherence times. It has been identified two classes of centres, emitting either at 620 nm or at 646.8 nm. While the emission at 620 nm has widely been attributed to the negatively charged of the SnV defects, the 646.8 nm line requires further investigations. Indeed, the aim of this Thesis work is to characterize the optical properties of both lines at room temperature and at cryogenic temperatures. Furthermore, a statistical study of the charge state as a function of surface termination was carried out. The investigation of the optical properties of tin-related colour centres was performed at the University of Turin and at the University of Ulm in the context of an Erasmus traineeship. This thesis summarizes the state of the art of research in this area and describes the work carried out according to the following organization: Chapter 1: introduction of diamonds as an appealing material for quantum optics. Description of its main properties and of the processes for its growth. Illustration of the known optical properties of group-IV colour centres, focusing on the tin-vacancy defects. Introduction to the single photon sources and description of the used technique for their characterisation. Chapter 2: detailed description of the employed experimental setups. Chapter 3: illustration of the experimental work and of the obtained results. This chapter is divided into two main sections. The first one shows the investigation of the 620 nm line. The second one, rather, describes the characterization of the 647 nm zero-phonon line.