Parametric Amplification in a Superconducting Microstrip Transmission Line

Broadband parametric amplifiers (PAs), which utilize the nonlinear kinetic inductance of superconducting transmission lines, provide new access to ultimate sensing capability for radio astronomical observation and microwave quantum electronics. In this paper, the parametric amplification is investigated with a time-domain numerical method. The results present direct images of the traveling waves, which clarify the distinctively different features of the parametric gain in uniform and impedance-perturbed nonlinear transmission lines. The results indicate that the traveling-wave PAs (TWPAs) are susceptible to impedance mismatching because of the lack of isolation between the input and the output ports. In the experimental part of this paper, we tested, for the first time, microstrip TWPAs based on NbTiN. A parametric gain was observed at liquid helium temperature.