Electro-optic correlations improve an efficient mechanical converter

An optical network of superconducting qubits is an appealing platform for quantum communication and distributed quantum computing, but developing a quantum-compatible link between the microwave and optical domains remains an outstanding challenge. Operating at the required T < 100 mK temperatures, we demonstrate a microwave-mechanical-optical converter with 47% conversion efficiency, and use a feedforward protocol to reduce added noise to 38 photons. The feedforward protocol harnesses our discovery that noise emitted from the two converter output ports is perfectly correlated, meaning that it saturates a bound for classical correlations. We also discuss a quantum feedforward protocol that, given high system efficiencies, allows quantum information to be transferred through a thermally excited mechanical oscillator.