Towards a coherent spin-phonon interface in diamond*

Mechanical vibrations interact with a variety of quantum systems, and can serve as a channel between qubits with different physical realizations. Here, we describe our experimental efforts towards a coherent interface between phonons and a spin qubit. The spin qubit of our choice is the silicon-vacancy (SiV) color center in diamond. A combination of the large response of the SiV spin to oscillating strain from phonons, and the confinement of relevant phonons in compact mechanical modes provided by optomechanical crystals (OMCs) will allow strong coupling with MHz single-phonon coupling rates. Towards this end, we establish the strain response of the SiV spin using a nanoscale cantilever, and measure a large strain susceptibility of 100 THz/strain. In parallel, we demonstrate high quality-factor (10⁵) GHz frequency mechanical modes in diamond OMCs. With current experimental parameters, this platform will allow laser cooling of the mechanical resonator at 4 K, and phonon-mediated two-qubit gates as well as quantum non-linearities for single phonons at mK temperatures.