Abstract
Being able to control the physical properties of individual quantum systems has triggered the boom of the field of quantum technologies aimed at creating new components and machines with functionalities unmatched by conventional physical systems. Among the quantum systems studied, the optically active point defects in semiconductors have the advantage of behaving like artificial atoms in the solid state. Isolated on an individual scale, they exhibit an emission of single photons that can be used for quantum communications. Some defects also have a controllable electronic spin that can serve as a quantum memory and a nanoscale quantum sensor. The NV center of diamond is currently by far the most studied fluorescent defect because its quantum properties can be exploited at room temperature. However, the ideal platform for developing large-scale technologies is silicon. Still, this semiconductor was left out because of its low bandgap energy. In fact, no optically active defect had been detected in it at the start of this thesis.After initial work on the NV center and its state of charge conversion dynamics, the core of this thesis was devoted to the study of fluorescent defects in silicon to be able to isolate them on an individual scale. This objective first required the development of a new optical microscopy setup at low temperature, optimized for the near infrared. The first efforts were devoted to the detection of a defect based on carbon impurities, called the G center, which exhibits an optical emission at telecom wavelengths suitable for propagation in optical fibers, and potentially advantageous spin properties for quantum technologies. The exploration of carbon-implanted silicon samples enabled the detection of single G centers, but also uncovered seven other families of individual fluorescent defects not listed in the literature on ensemble measurements. In parallel, individual defects associated with a complex of interstitial silicon atoms were also observed in another silicon sample. The analysis of the emission of single photons from these different emitters, as well as their optical spectroscopy, made it possible to determine properties inaccessible on the ensemble measurements.The detection of individual optically active defects in silicon opens a new path for quantum technologies in this learning material of the semiconductor industry. One of the next challenges will be to demonstrate the control of the spin states associated with these unique defects. Beyond quantum applications, the study at the individual scale of fluorescent silicon defects could also bring new discoveries on these systems of both fundamental and applied interest.