ENGINEERING ACOUSTIC WAVE ON SOLID STATE QUANTUM MATERIAL

Solid state spin is a rapidly developing system for quantum sensors and computers.

With the development of fabrication technology, since 2013, microelectromechanical systems (MEMS) technology began to be integrated with mechanical strain coupled to the spin system, instead of a traditional microwave antenna. Subsequently, the ability of quantum control in this system was greatly extended. In one example, strain has been demonstrated to be useful in dynamical decoupling, which increases the T2* of a diamond NV center.

Since the first work on strain-spin coupling in diamond, research has been greatly broadened to include SiC, graphene, transition metal dichalcogenide (TMD) monolayers and other quantum systems. Mechanical transducers, cantilevers, surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators have been proposed and fabricated to induce mechanical strain. Consequently, an urgent problem to be solved is how to design the mechanical system that works best for a given spin application? That is, how do we place the maximum strain on a specific atom position in a material? Traditional MEMS figures of merit might not apply, because mechanical resonance functions in a much larger volume, whereas spin functions at the atomic level.

To solve this problem, this thesis explores different branches of MEMS technology and

compares them for spin-phonon coupling applications. First, cantilever and clamped-clamped beam devices on SiC and diamond are demonstrated, according to the fabrication technique that we developed at Purdue. The SiC lateral overtone bulk acoustic wave resonator (LOBAR) with decreased anchor loss is then introduced. Using the knowledge gained in this process, I propose a wafer level phononic crystal structure that can limit the mechanical frequency on a device wafer and thus reduce the noise. Finally, because a resonator is not the only MEMS technology that can induce strain, I explore MEMS actuators with an acoustic Fresnel zone plate device based on diamond, which can focus an acoustic wave onto the spin location.