Superconducting Kinetic Inductance-Based On-Chip Frequency Conversion

In addition to the standard geometric inductance, superconductors have a kinetic inductance that can have a strong quadratic dependence on current. We use this nonlinearity to generate large harmonics of GHz signals by etching a 0.5 m long meandered coplanar waveguide from a 60 nm thick NbTiN sputtered film. After cooling the fabricated chip to 3 K, we measure a maximum on-chip conversion efficiency from 10 GHz to 20 GHz of 14% when applying a 2.5 dBm 10 GHz signal and a 20 rnA dc current bias. The measured powers up to the third harmonic and changes in phase agree with harmonic balance simulations of the nonlinear system. We anticipate that further optimization of the design including frequency dispersion engineering will significantly increase the conversion efficiency. This approach and material, which has a critical temperature above 15K, is also extendable up to THz frequencies; we chose to operate at 10s of GHz based on the available instruments and cabling.