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
(VBββ) in hexagonal boron nitride (hBN), we grow
isotopically purified h10B15N crystals
for the first time. Compared to VBββ in hBN with the
natural distribution of isotopes, we observe substantially narrower and less
crowded VBββ spin transitions as well as extended
coherence time T2β and relaxation time T1β. For quantum sensing,
VBββ centers in our
h10B15N samples exhibit a factor of 4
(2) enhancement in DC (AC) magnetic field sensitivity. For quantum registers,
the individual addressability of the VBββ hyperfine
levels enables the dynamical polarization and coherent control of the three
nearest-neighbor 15N 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.Comment: 8+4+8 pages, 4+4+6 figure