Spin-state selective excitation in spin defects of hexagonal boron nitride

Hexagonal boron nitride (hBN) has emerged as a promising platform for quantum sensing, leveraging its optically addressable negatively charged boron vacancy (V^B) spin defects for sensing, and the ability to transfer thin hBN flakes onto materials or devices of interest. However, large hyperfine interactions cause overlap in spin transition spectra, hindering magnetic sensitivity, thus requiring new approaches to enhance the V^B magnetic sensitivity. Here we demonstrate microwave polarization induced spin-selective excitation of V^B spin transitions in He+ ion irradiated hBN using cross-shaped microwave waveguide. We scan the relative phase of two orthogonal linearly polarized microwave sources, generated from an RFSoC FPGA, and interfere them at a central cross of our microwave waveguide. The selective spin transitions are demonstrated through optically detected magnetic resonance (ODMR) spectra with phase-selective |0> <-> |-1> or |0> <-> |+1> excitation of V^B defects. This technique demonstrates ability to selectively address spin transitions making hBN a more powerful platform for quantum sensing, particularly important at low magnetic fields, by mitigating the low-field overlap of hyperfine broadened spin transitions.