Coherent millimeter-wave transduction with lithium niobate electro-optics

Superconducting systems, while promising for quantum computation, are limited by dilution refrigerator space constraints. To overcome these constraints and to construct quantum networks, frequency converters are needed. In this work, we demonstrate an integrated millimeter-wave-to-optical electro-optic transducer on a lithium niobate-on-sapphire platform. By utilizing millimeter-wave frequencies we obtain an increase in the electro-optic coupling rate and we can operate at higher temperatures, which allows for using greater optical pump power. This transducer is a triply-resonant system consisting of two optical modes (~1521 nm, ~1521.7 nm) of a racetrack resonator plus a NbN superconducting resonator (~105 GHz). Our device is packaged to interface with WR10 waveguide ports, while also maintaining fiber optical access to couple light onto the chip via grating couplers. We measure photon number conversion efficiency and transduction bandwidth as a function of pump power at 4 K. We are predominantly limited by the quality factor of the millimeter-wave mode. With improvements to efficiency, our transducer could be included in a microwave-optical conversion scheme, or as an entangled photon-pair source.