Engineering Boron Vacancy Defects in Boron Nitride Nanotubes.

Spin defects in hexagonal boron nitride (hBN) are emerging as promising platforms for quantum sensing applications. In particular, the negatively charged boron vacancy ( V _B ^- ) centers have been engineered in bulk hBN and few-layer hBN flakes, and employed for sensing. Here, we investigate the engineering of V _B ^- spin defects in boron nitride nanotubes (BNNTs). The generated spin defects are distributed along and around the BNNTs. Moreover, in contrast to hBN flakes, the spins in BNNTs exhibit a directional response relative to the direction of a surrounding magnetic field, which is consistent with the tubular geometry. The unique geometry of BNNTs allows for a more controlled and predictable placement of spin defects compared to bulk hBN, paving the way for innovative sensing applications with high spatial resolution and optomechanical studies of spin defects in hBN.