Techniques regarding microwave-to-optical quantum transducers are provided. For example, one or more embodiments described herein can include an apparatus that can include a microwave resonator on a dielectric substrate and adjacent to an optical resonator, and a photon barrier structure at least partially surrounding an optical resonator, wherein the photon barrier structure is configured to provide isolation of the microwave resonator from optical photons in the dielectric substrate outside the photon barrier structure.