Polymorphs of 17O-Implanted ST1 Spin Centers in Diamond and Spectroscopy of Strongly Coupled 13C Nuclear Spins

The so-called ST1 center in diamond is one of the very few known systems today that possesses properties similar to the nitrogen-vacancy (NV) center. The ST1 enables spin coherent control at room temperature with even larger readout contrast than NV centers and is therefore promising for quantum information or sensing at 300 K. However, the nature and methods of on-demand creation of the ST1 were still unknown and a large dispersion of the optical, spin properties, and photostability was reported. Here, using two independent methods, we definitely evidence that the ST1 center is made of oxygen. Contrarily to previous studies where the ST1 centers were found scarcely (likely created unintentionally by oxygen-plasma treatments), the centers are created here reproducibly by oxygen implantation in several samples and enable a comprehensive study of their "bulk" optical and spin properties. Electron spin resonance line widths as low as 330 kHz were measured, indicating electron spin coherence time T2* in the μs range at 300 K. Further, we report on the hyperfine interaction with 17O and with nearby 13C nuclear spins. Twenty different coupling types with 13C larger than 2.5 MHz are found. This highlights the low symmetry of the ST1, the presence of at least one carbon vacancy in the ST1 structure, and the possibility to address a larger number of discernible 13C nuclear spins than with the NV center. These results open the way to the creation and use of quantum registers or nuclear spin memories with a long coherence time based on ST1 centers, which also have potential for quantum sensing.