Taekwan Yoon

Bulk acoustic resonators support robust, long-lived mechanical modes, capable of coupling to various quantum systems. In separate works, such devices have achieved strong coupling to both superconducting qubits, via piezoelectricity, and optical cavities, via Brillouin interactions.

Here, we discuss piezoelectric and Brillouin interactions between phonons and microwave/optical photons, as well as microwave and bulk acoustic resonators that enable the interactions. Based on the understanding of these elements, we then present a novel hybrid microwave/optical platform that exploits resonantly enhanced Brillouin interactions and piezoelectric couplings to efficiently access phonons within a variety bulk crystalline materials (quartz, CaF₂, Si, etc) using tunable microwave and optical cavities.

The high optical sensitivity and ability to apply large resonant microwave field in this system offers a new tool for probing anomalous electromechanical couplings, which we demonstrate by investigating (nominally-centrosymmetric) CaF₂ and revealing a parasitic piezoelectricity of 83 am/V. Additionally, we attempt to probe electromechanical response in Si, where we are able to provide an upper bound to its parasitic piezoelectricity.

We further show how this device functions as a bidirectional electro-opto-mechanical transducer using a piezoelectric crystal, x-cut quartz, with transduction efficiency exceeding 10^-8, and lay out a feasible path towards unity conversion efficiency. Such studies are important topics for emerging quantum technologies, and highlight the versatility of the new hybrid platform introduced.