Piezo-optomechanical Actuation of Nanobeam Resonators for Microwave-to-Optical Transduction

We demonstrate three methods for microwave actuation of GaAs nanobeam piezo-optomechanical resonators, based on interdigitated transducers, piezoelectric resonators, and micro-antenna structures. Potential applications of these devices range from bi-directional microwave-to-optical conversion to optomechanical thermometry.

Long-distance quantum networks based on superconducting quantum circuit nodes require an efficient quantum transducer that can bi-directionally convert information between the microwave (MW) and optical domains. Piezoelectric devices coupled to cavity optomechanical systems have been employed in such frequency conversion [1]-[4], but the transduction efficiency remains low because of the challenging design and fabrication requirements. An efficient MW-to-optical transduction calls for optimized conversion of all the steps from electrical to mechanical to optical. GaAs nanobeam optomechanical crystal (OMC) resonators are excellent candidates for mechanical-to-optical transduction because of the high optomechanical coupling strength of GaAs (the highest of any piezoelectric platform [2],[5]). As a result, GaAs nanobeam resonators have been demonstrated in mechanical-to-optical transduction, including when the thermal occupation of mechanical resonator is cooled to the quantum ground state [4]. However, the initial step of MW-to-mechanical transduction in this system remains a challenge, due to problems such as weak piezoelectric coupling and large MW impedance. Here, we report progress on three different methods for MW-to-mechanical transduction in GaAs nanobeam piezo-optomechanical resonators: (i) using piezoelectric interdigitated transducers (IDTs) [3], (ii) using a piezoelectric resonator whose shear mode frequency is designed to match the fundamental mechanical mode frequency of the nanobeam, leading to the formation of a resonant mechanical super-mode, as theoretically proposed in Ref. [5], and (iii) using near-field MW probes that offer broadband actuation without introducing new mechanical modes, and have relevance in sensing and thermometry.