Probing spin-phonon interactions in semiconductors with x-rays and Gaussian acoustics*

Coupling defect spins to phonons provides routes to new quantum control methods, coherence protection, and integrating spin qubits with quantum transducers. Silicon carbide (SiC) substrates host optically addressable point defects with long-lived electronic spin registers. Additionally, SiC is a low loss acoustic material and supports wafer-scale fabrication techniques, making SiC an ideal material for hybrid spin-mechanical systems. We fabricate surface acoustic wave (SAW) resonators taking advantage of isotropic acoustic propagation properties to construct simple Gaussian geometries, which focus strain and minimize diffraction losses. We directly image the mechanical mode with nanometer-scale spatial resolution by using hard x-ray diffraction microscopy and frequency matching a SAW to the timing structure of a synchrotron [1]. The SAW resonators are then utilized for coherent manipulation of divacancy electron spin ensembles in the SiC. We demonstrate all-optical detection of acoustic paramagnetic resonance, which enables quantum sensing of phonons without magnetic microwaves. In addition, we measure coherent magnetically forbidden spin transitions with Autler-Townes splittings and Rabi oscillations on the divacancy spins, as well as show spatial mapping of spin driving which reveals spin coupling to shear [2]. Our model, comprising of ab initio calculations for the spin-strain coupling parameters, captures the salient features of the physics. These results offer a basis for three-level spin system control with phonons and paths to combining spin registers with nanomechanical devices.

[1] S. J. Whiteley et al., arXiv:1808.04920 (2018).
[2] S. J. Whiteley et al., arXiv:1804.10996 (2018).

In collaboration with G. Wolfowicz, C. P. Anderson, A. Bourassa, H. Ma, M. Ye, G. Koolstra, K. J. Satzinger, M. V. Holt, F. J. Heremans, A. N. Cleland, D. I. Schuster, G. Galli, D. D. Awschalom