mm-Wave superconducting mode converter for kinetic inductance parametric amplifier

In the past decade, there has been a great attention towards using millimeter wave (mm-wave) technology in various applications among which is superconducting quantum devices. At mm-wave frequencies, quantum devices are less sensitive to thermal background noise and hence can be built at higher temperatures than quantum devices operating at microwave frequencies. Kinetic Inductance parametric amplifier (KIPA) is one crucial component in the superconducting qubit circuit system. These parametric amplifiers with their wide bandwidth, quantum-limited noise performance and high dynamic range are well suited to be used as readout amplifiers. The large kinetic inductance is achieved using a thin film of high resistivity superconducting material. However, to couple the KIPA to W-band waveguide feeds, a superconductor-based transition device is needed with low losses. In this work, we design and test a superconducting mode converter to be used as low-loss transitional component to convert the W-band waveguide mode (TE10) to the quasi-TEM mode supported by the KIPA. It uses a ridge gap waveguide design to eliminate the dielectric losses. We present field simulations as well as the experimental results of testing the superconducting mode converter at low temperature.