Exploring the Properties of the VB- Defect in hBN: Optical Spin Polarization, Rabi Oscillations, and Coherent Nuclei Modulation.

Optically active point defects in semiconductors have received great attention in the field of solid-state quantum technologies. Hexagonal boron nitride, with an ultra-wide band gap Eg = 6 eV, containing a negatively charged boron vacancy (VB-) with unique spin, optical, and coherent properties presents a new two-dimensional platform for the implementation of quantum technologies. This work establishes the value of VB- spin polarization under optical pumping with λext = 532 nm laser using high-frequency (νmw = 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. In optimal conditions polarization was found to be P ≈ 38.4 %. Our study reveals that Rabi oscillations induced on polarized spin states persist for up to 30‑40 µs, which is nearly two orders of magnitude longer than what was previously reported. Analysis of the coherent electron-nuclear interaction through the observed electron spin echo envelope modulation (ESEEM) made it possible to detect signals from remote nitrogen and boron nuclei, and to establish a corresponding quadrupole coupling constant Cq = 180 kHz related to nuclear quadrupole moment of 14N. These results have fundamental importance for understanding the spin properties of boron vacancy.&#xD.