Towards quantum optomechanics using bulk acoustic wave resonators

Superconducting circuits are one of the most sophisticated architectures for quantum information processing to date. MW-to-optical conversion in the quantum regime could enhance their scalability and range of applications, since optical photons can be used as noise-free carriers of quantum information that connect circuits in different refrigerators. This requires conversion that is coherent, efficient, and with minimal added noise, which has not been demonstrated yet.
We present our advances in developing a cryogenic cavity optomechanical device based on a bulk-acoustic-wave (BAW) mechanical resonator, which can act as an essential part of a MW-to-optical transducer. Strong coupling to BAWs has been demonstrated both for microwave photons [1] and for optical photons [2]. Building on these works, we are developing an optomechanical system that is also compatible with coupling to superconducting circuits. We report on first experiments of BAW resonators cooled to millikelvin temperatures and coupled to optical cavity modes. As a first proof-of-principle, we discuss prospects for storage and retrieval of low-photon-number coherent optical states in the mechanical resonator.

[1] Chu et al., 2017, Science 358(6360).
[2] Kharel et al., 2018, Arxiv 1812.06202.