Piezoelectrically driven diamond phononic nanocavity by phonon-matching scheme for quantum applications

Efficiently exciting and controlling phonons in diamond nanoresonators represents a fundamental challenge for quantum applications. Here, we theoretically demonstrate the possibility of exciting mechanical modes within a double hybrid cavity (DHC), formed by adjoining to a diamond cavity a second cavity made of aluminum nitride. The latter is piezoelectric and serves as a microwave-to-phonon transducer, activating mechanical modes in the entire DHC. We show the process of matching the cavities' phononic properties, making them work coordinately in the DHC and obtaining a well-confined mode. In the diamond part of the cavity, this mode replicates the fundamental mode of the individual diamond cavity, showing that the piezoelectric transducer does not alter the diamond individual fundamental mode. In the piezoelectric part, the strong confinement of stress and electric field results in a high piezoelectric coupling rate, demonstrating the effectiveness of a phononic cavity as a transducer. The study is contextualized in the framework of a quantum networking application, where the DHC serves as a spin qubit, exploiting the spin-mechanical coupling within diamond color centers.