Rotation of the center-of-mass of single fluorescent defects in silicon*

The boom of silicon in semiconductor technologies was closely tied to the ability to control its density of lattice defects. After being regarded as detrimental to the crystal quality in the first half of the 20th century, point defects have become an essential tool to tune the electrical properties of this semiconductor, leading to the development of a flourishing silicon industry. At the turn of the 21^st century, progress in Si-fabrication and implantation processes has triggered a radical change by enabling the control of these defects at the single level. This paradigm shift has brought silicon into the quantum age, where individual dopants are nowadays used as robust electrical quantum bits to encode and process quantum information. Fluorescent defects recently isolated at single-defect scale in silicon could follow suit.

Among the many color centers isolated in silicon over the past three years, the G center has attracted particular attention because it combines telecom single-photon emission with a metastable spin triplet that could potentially be used as a qubit. As demonstrated in recent theoretical studies, this defect is said to present a remarkable microscopic configuration associated with a rotational dynamics. However, the rotation of the G center has never been demonstrated on the scale of a single defect. In this talk, we will investigate individual G centers in silicon through low-temperature photoluminescence measurements. We will reveal a fine structure in their photoluminescence spectra and multipolar emission that are compatible with a model of center-of-mass rotation of G centers during optical excitation. Using symmetry point group theory, we will model the rotational states of the center G under external perturbations to identify the dominant interaction producing the observed fine structures. These results highlight the rich physics of this quantum system and open the way to exploring its rotational quantum degree of freedom.