We are developing high-efficiency microwave impedance transformers for microwave-to-optical quantum transducers. Our goal is to match a standard 50 Ω microwave environment to a novel high-impedance electro-optic (EO) device based on a 20 kΩ thin-film lithium niobate (TFLN) traveling-wave modulator. The high impedance increases the microwave field in the EO device and improves the overall transduction efficiency. We will use a Klopfenstein taper design, as it provides low reflection with a compact length over a broad bandwidth. We target 4–8 GHz operation and near-unity coupling to the 20 kΩ modulator. We will implement the taper using NbTiN thin-film nanowire superconducting transmission lines. NbTiN is well suited to this application because of its relatively high critical temperature and high kinetic inductance, which enables compact, high-impedance transmission lines. The TFLN platform also introduces piezoelectric loss because microwave energy can couple to acoustic modes and radiate away from the EO region. To suppress this loss, we are developing chirped phononic-crystal tethers that isolate the suspended TFLN structure from bulk acoustic modes over a broad frequency range. By combining NbTiN high-kinetic-inductance transmission lines and a Klopfenstein impedance profile with phononic isolation, this project aims to deliver a low-loss, broadband, and scalable microwave interface for efficient microwave-to-optical quantum transduction.
Project is currently funded by: Federal