Microwave-to-optics transduction is emerging as a vital technology for scaling quantum computers and quantum networks. To establish useful entanglement links between qubit processing units, several key conditions have to be simultaneously met: the transducer must add less than a single quantum of input referred noise and operate with high-efficiency, as well as large bandwidth and high repetition rate. We have developed a new design for an integrated transducer based on a planar superconducting resonator coupled to a silicon photonic cavity through a mechanical oscillator made of lithium niobate on silicon. During the first phase of the project, we have designed, fabricated and experimentally demonstrated the unique performance and potential of our novel transducer platform for simultaneously realizing all of the above conditions, measuring added noise that is limited to a few photons, transduction efficiencies as high as 0.9%, with a bandwidth of 14.8 MHz and a repetition rate of up to 100 kHz. Our device couples directly to a 50-Ω transmission line and can easily be scaled to a large number of transducers on a single chip, paving the way for distributed quantum computing. Device performance is already at the point of enabling qubit readout and control through optical channels, as well as monitoring of ultra-low power microwave signals in the cryogenic environment. During the second phase of the project, we have improved the performance of our transducer, including through increased electromechanical efficiency. This has allowed us to use the transducer to perform optical readout of a superconducting qubit, measured microwave power down to 100's of aW through a pilot with a quantum computing company.
