Acoustic probing of spin-phonon interactions for solid-state defects in the quantum regime.

Understanding spin-phonon interactions is essential for solid-state quantum technologies that exploit the spin degree of freedom. Experimental probes for spin-phonon interaction in the quantum regime are therefore needed. We develop a versatile technique to probe the resonant coupling of solid-state defects to strain in the absence of thermal motion. Our technique consists in measuring high overtone frequency bulk acoustic wave resonators (HBAR) at 50 mK, in crystals hosting spin defects. By bonding a thin-film lithium niobate transducer onto the host crystal, we couple to its HBAR modes at GHz frequencies. Preliminary results demonstrate that we observe the characteristic acoustic response of HBAR structures and show the potential to measure spin-strain coupling for various crystal targets. This technique could be use to identify spin species suitable to acheive coherent spin-phonon interactions.