Synthesis and characterization of quantum-grade diamond

The use of solid-state spin defects as qubits for quantum applications requires long spin coherence times (defined as the maximum duration a system can remain in a prepared quantum state). This coherence time is limited by the interaction of spin qubits with the magnetic noise resulting from the surrounding electron and nuclear spin bath. The quality of the host material is thus an essential factor for the development of high performance solid-state qubits.

Based on our recognized expertise in the field of diamond synthesis by plasma enhanced chemical vapour deposition (PECVD), we work on the development of quantum-grade diamond, presenting ultra-high isotopical and structural purity compared to commercially available materials. This work involves the optimization of PECVD reactors and epitaxial growth parameters for the preparation of high-quality single crystal diamond layers.

Another objective is the formation of spin defects with controlled density, depth, charge state and coherence time by in-situ doping during PECVD. The properties and location of color centres in the diamond crystal can be engineered, for example through co-doping with different atoms or by etching and selective CVD overgrowth of diamond. Our research is particularly focused on the fabrication of doped single-crystal materials presenting optimal properties for the photoelectric readout of spin states. In parallel, we also investigate the seedless PECVD growth of doped nanodiamonds presenting high crystal quality, controlled size and long T₁ spin coherence times, which are required for nanoscale quantum sensing especially in biological environment.

The optimization of the host material quality, as well as the study of the spin defects formation mechanism and the assessment of their quantum properties is based on the feedback of in-house characterization of structural, optical, photoelectric and spin properties by various advanced techniques including SEM, AFM, confocal microscopy, photoluminescence and photocurrent spectroscopy, time of flight and spin coherence measurements.