Cavity electro-optic circuit for microwave-to-optical conversion in the quantum ground state

In the development of microwave-to-optical (MO) quantum transducers, suppressing added noise induced by optical excitation remains a major challenge. Here we report an integrated superconducting cavity electro-optic circuit based on single crystalline thin-film aluminum nitride ultralow microwave and losses. We demonstrate efficient bi-directional MO conversion at milli-Kelvin temperatures, with near-ground state thermal $({\overline{n}}_{\mathrm{e}}=0.09\ifmmode\pm\else\textpm\fi{}0.06)$, despite peak power drive exceeding cooling dilution refrigerator mixing chamber. Our dynamical study further reveals different light-induced generation mechanisms provides crucial guidelines for optimizing circuits in future hybrid microwave-optical links.