We demonstrate single spin spectroscopy of a fluorescent tumbling defect in silicon called the G center, behaving as a pseudo-molecule randomly reorienting itself in the crystalline matrix. Using high-resolution spin spectroscopy, we reveal a fine magnetic structure resulting from the spin principal axes jumping between discrete orientations in the crystal. Modeling the atomic reorientation of the defect shows that spin tumbling induces variations in the coupling to the microwave magnetic field, enabling position-dependent Rabi frequencies to be detected in coherent spin control experiments. By virtue of its pseudo-molecule configuration, the G center in silicon is a unique quantum system to investigate the mutual interaction between optical, spin and rotation properties in a highly versatile material.
@article{arxiv.2510.15590,
title = {A single optically detectable tumbling spin in silicon},
author = {Félix Cache and Yoann Baron and Baptiste Lefaucher and Jean-Baptiste Jager and Frédéric Mazen and Frédéric Milési and Sébastien Kerdilès and Isabelle Robert-Philip and Jean-Michel Gérard and Guillaume Cassabois and Vincent Jacques and Anaïs Dréau},
journal= {arXiv preprint arXiv:2510.15590},
year = {2026}
}