Strontium Titanate Traveling-Wave Parametric Amplifiers

Traveling wave parametric amplifiers (TWPAs) with added noise approaching the quantum limit have enabled highly sensitive microwave frontends for qubit readout, radio astronomy, and particle physics. These amplifiers operate by mixing a strong microwave pump wave with the signal in a nonlinear waveguide, in such a way that a fraction of the pump power is used to amplify the signal and generate a co-propagating idler wave. Conventional TWPAs rely on the inductive nonlinearity originating from the Josephson effect or kinetic inductance in thin superconductors, restricting these devices to use cases below 4~K and nonmagnetic environments. In this work, we propose a TWPA based on the nonlinear dielectric strontium titanate (STO). The nonlinear properties of STO remain stable at much higher temperatures (20 K) and in high magnetic fields. We have developed a theoretical framework for the optimal geometry of STO-based nonlinear transmission lines to achieve phase-matched parametric processes while minimizing the required pump power. Periodically loaded coplanar-waveguide (CPW)-like structures on thin-film STO are simulated to have 20 dB of gain over 100 mm of interaction, based on empirical nonlinear models of STO. Alternative methods including slotline geometries and bulk STO are also simulated. Preliminary measurements of thin-film STO properties and amplifiers are presented.