Coherent spin control of the G center in silicon: from ensembles to single defects

Félix Cache

Silicon lies at the heart of the microelectronics and photonics industries and benefits from the most advanced growth and nanofabrication processes. Building on these advantages, it has emerged as a platform of choice to develop promising quantum technologies such as electrically controlled spin qubits and quantum photonic circuits. In 2020, the first optical isolation of a color center in silicon at the single-defect level was a major breakthrough, offering new perspectives for the development of deterministic single-photon sources and spin–photon interfaces directly integrated into silicon. Since then, many other defects have been isolated at the single scale, some attractive for their optical properties and others for their spin states. Among these, the G center, a carbon-based complex emitting in the telecom O-band, has been extensively studied recently for its optical characteristics. This thesis focuses on the properties of its spin triplet state, located in a metastable photo-excited level. First, we investigate the photodynamics of the metastable spin triplet level of G-center ensembles in order to design the optimal pulse sequence for the optical detection of its magnetic resonances. We then demonstrate the first coherent control of the electron spin of a G-center ensemble and investigate its spin coherence properties. After, to enable the coherent spin control of single G centers, we integrate individual defects into photonic microcavities to enhance their photoluminescence signal. Finally, single-spin spectroscopy measurements allow to evidence a fine spin structure resulting from the spin tumbling motion of the G center between discrete orientations in the crystal. This work reveals the G center in silicon as a complex physical system with interplaying telecom photon, spin and rotation degrees of freedom in the most mature platform for nanofabrication.