Mechanically Mediated Microwave Frequency Conversion in the Quantum Regime.

We report the observation of efficient and low-noise frequency conversion between two microwave modes, mediated by the motion of a mechanical resonator subjected to radiation pressure. We achieve coherent conversion of more than 10^{12}  photons/s with a 95% efficiency and a 14 kHz bandwidth. With less than 10^{-1}  photons·s^{-1}·Hz^{-1} of added noise, this optomechanical frequency converter is suitable for quantum state transduction. We show the ability to operate this converter as a tunable beam splitter, with direct applications for photon routing and communication through complex quantum networks.