Isotope engineering for spin defects in van der Waals materials

Abstract

Spin defects in van der Waals materials offer a promising platform for advancing quantum technologies. Here, we propose and demonstrate a powerful technique based on isotope engineering of host materials to significantly enhance the coherence properties of embedded spin defects. Focusing on the recently-discovered negatively charged boron vacancy center (${\mathrm{V}}_{\mathrm{B}}^{-}$) in hexagonal boron nitride (hBN), we grow isotopically purified $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$ crystals. Compared to ${\mathrm{V}}_{\mathrm{B}}^{-}$ in hBN with the natural distribution of isotopes, we observe substantially narrower and less crowded ${\mathrm{V}}_{\mathrm{B}}^{-}$ spin transitions as well as extended coherence time $T_2$ and relaxation time $T_1$. For quantum sensing, ${\mathrm{V}}_{\mathrm{B}}^{-}$ centers in our $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$ samples exhibit a factor of $4$ ($2$) enhancement in DC (AC) magnetic field sensitivity. For additional quantum resources, the individual addressability of the ${\mathrm{V}}_{\mathrm{B}}^{-}$ hyperfine levels enables the dynamical polarization and coherent control of the three nearest-neighbor ${}^{15}\mathrm{N}$ nuclear spins. Our results demonstrate the power of isotope engineering for enhancing the properties of quantum spin defects in hBN, and can be readily extended to improving spin qubits in a broad family of van der Waals materials.

8+5+12 pages, 4+5+8 figures