Optomechanical quantum control of long-lived phononic modes in microfabricated high overtone bulk acoustic wave resonators

We present a novel optomechanical system that allows for quantum control of individual high-coherence phonon modes supported by microfabricated high-overtone bulk acoustic wave resonators (μHBARs). The unique properties of bulk-based acoustic resonators, such as excellent thermal anchoring and robustness against decoherence, position them as a promising platform for realization of optomechanical systems with high efficiency photon-phonon conversions which could be utilized for different applications, including quantum repeaters and heralded single photon sources. We use this system to demonstrate laser cooling of ultra-massive (7.5 micrograms) high-frequency acoustic mode to its ground state. This achievement, to the best of our knowledge, represents the most massive mechanical object laser cooled to its quantum ground state to date. Through these laser cooling experiments, no absorption-induced heating was observed, showcasing the robustness of our platform against parasitic heating— a long-standing issue that similar optomechanical platforms suffer from. Our results demonstrate the potential of μHBAR based optomechanical systems for future advancements in quantum gate operations and deterministic quantum interactions leading to the development of scalable quantum systems.