Optomechanical ground-state cooling in a continuous and efficient electro-optic transducer

Coherent transduction of quantum states between microwave and optical frequencies would allow interfacing distant superconducting quantum computers. Thermal noise from occupation of involved modes presents a challenge for all transduction platforms. In particular, for membrane-based electro-optomechanical transducers, occupation of the low-frequency intermediate mechanical mode has been a problematic contribution to the input-referred added noise. By performing motional sideband-asymmetry thermometry, we demonstrate ground-state cooling of the mechanical mode in such a transducer during continuous operation while maintaining high transduction efficiency. Furthermore, the microwave circuit is minimally affected by the optical pump, even at powers two orders of magnitude greater than that needed for ground-state cooling. Though we cool the mechanical mode to its ground state, microwave pump-induced noise on the superconducting circuit limits the transducer performance, preventing transduction with less than one photon/s/Hz of input-referred added noise.