Microwave-to-Optical Quantum Transduction with Optomechanical Nanobeam Heterostructures

The quantum transduction, or equivalently quantum frequency conversion, between microwave and optical photons is essential for the realization of scalable quantum computers with superconducting qubits. Due to the large frequency difference between them, the transduction needs to be done via intermediate bosonic modes or nonlinear processes. So far, the transduction via the optomechanical effect, i.e., via phonons, has attracted attention as a promising method toward high-efficiency and low-noise transduction. It is well known that one of the ways for improving the transduction efficiency is to increase the optical input pump power. However, as a trade-off, there will be an increase in the environmental temperature, which can affect the nearby superconducting qubits. In this work, we theoretically propose a way to improve the transduction efficiency in optomechanical systems by introducing optomechanical nanobeam heterostructures. Such a heterostructure consists of N layers of an optomechanical crystal nanobeam and N layers of an insulator. We show that the electromechanical and optomechanical coupling strengths are both enhanced by the factor N^1/2 compared to the single-layer case. As the result, the electromechanical and optomechanical cooperativities are also enhanced by the factor N compared to the single-layer case, giving rise to the enhanced microwave-optical transduction efficiency.