Simultaneous Brillouin and piezoelectric coupling to a high-frequency bulk acoustic resonator

TL;DR

This paper introduces a hybrid microwave/optical platform that couples to bulk acoustic waves via cavity-enhanced piezoelectric and photoelastic interactions, enabling strong optomechanical coupling and bidirectional transduction for quantum applications.

Contribution

It presents a novel, tunable hybrid system integrating microwave, optical, and acoustic components, demonstrating strong coupling, high cooperativity, and potential for efficient quantum transduction.

Findings

Achieved fully resonant interactions between microwave, optical, and acoustic modes.

Demonstrated high cooperativity using optical cavity enhancement.

Realized bidirectional electro-opto-mechanical transduction with quantum efficiency >10^-8.

Abstract

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. In this work, we present a novel hybrid microwave/optical platform capable of coupling to bulk acoustic waves through cavity-enhanced piezoelectric and photoelastic interactions. The modular, tunable system achieves fully resonant and well-mode-matched interactions between a 3D microwave cavity, a high-frequency bulk acoustic resonator, and a Fabry Perot cavity. We realize this piezo-Brillouin interaction in x-cut quartz, demonstrating the potential for strong optomechanical interactions and high cooperativity using optical cavity enhancement. We further show how this device functions as a bidirectional electro-opto-mechanical transducer, with quantum efficiency exceeding $10^{-8}$, and a feasible path towards unity conversion efficiency. The high optical sensitivity and ability to apply large resonant microwave field in this system also offers a new tool for probing anomalous electromechanical couplings, which we demonstrate by investigating (nominally-centrosymmetric) CaF$_2$ and revealing a parasitic piezoelectricity of 83 am/V. Such studies are an important topic for emerging quantum technologies, and highlight the versatility of this new hybrid platform.