Continuous and Time-Domain Coherent Signal Conversion between Optical and

A quantum network consisting of computational nodes connected by high-fidelity communication channels could expand information-processing capabilities significantly beyond those of classical networks. Superconducting qubits hold promise for scalable and high-fidelity quantum computation at microwave frequencies but must operate in an isolated cryogenic environment, obviating the potential for practical long-range communication. Quantum communication has, however, been demonstrated with optical photons. A fast efficient quantum-coherent interface between superconducting qubits and optical photons would provide a key resource for a large-scale quantum network or distributed quantum computer. Here, we describe the design and experimental operation of a device incorporating a silicon optomechanical nanobeam combined with an aluminum-nitride-based electromechanical transducer. We experimentally demonstrate classical continuous-wave operation of this device at room temperature with external conversion efficiencies of (2.5 +/- 0.4) x 10(-5) (microwave to optical) and (3.8 +/- 0.4) x 10(-5) (optical to microwave), corresponding to internal efficiencies of 2.4% and 3.7%, respectively. This device also has a larger bandwidth than previous efficient microwave-optical transducers, allowing us to operate in the time domain with 20-ns pulses.