Efficient integrated millimeter-wave cavity electro-optics transducer operating at room temperature

Efficient microwave-to-optical transduction enables conversion of quantum information between circuit microwave qubits and optical photons. Cavity electro-optics (EO), leveraging the Pockels effect, offers a direct path to this and, as the electro-optic analog of cavity optomechanics, shares the same parametric interaction physics driving precision measurements and fundamental studies. Previous cavity EO systems operated at 4–8 GHz and cryogenic temperatures using superconducting resonators. Here, we demonstrate an integrated cavity EO system at 59.33 GHz with 2.5% on-chip bidirectional photon transduction at room temperature—matching state-of-the-art cryogenic results without using superconductors. We show that the single-photon coupling rate scales linearly with frequency, making millimeter-wave (mmW) frequencies a promising regime for cavity EO studies. We demonstrate the direct resolution of Johnson–Nyquist noise in the mmW cavity, enabled by the efficient transduction. We also demonstrate operation as a low-noise mmW receiver with sub-ambient noise temperature and discuss potential performance improvements for cryogenic implementations.