Johannes Hubmayr

Broadband parametric amplifiers based on nonlinear kinetic inductance artificial transmission lines

  1. Saptarshi Chaudhuri,
  2. Dale Li,
  3. Kent Irwin,
  4. Clint Bockstiegel,
  5. Johannes Hubmayr,
  6. Joel Ullom,
  7. Michael Vissers,
  8. and Jiansong Gao
We present broadband parametric amplifiers based on the kinetic inductance of superconducting NbTiN thin films in an artificial (lumped-element) transmission line architecture. We demonstrate
two amplifier designs implementing different phase matching techniques: periodic impedance loadings, and resonator phase shifters placed periodically along the transmission line. Our design offers several advantages over previous CPW-based amplifiers, including intrinsic 50 ohm characteristic impedance, natural suppression of higher pump harmonics, lower required pump power, and shorter total trace length. Experimental realizations of both versions of the amplifiers are demonstrated. With a transmission line length of 20 cm, we have achieved gains of 15 dB over several GHz of bandwidth.
arxiv pdf

Frequency-tunable Superconducting Resonators via Nonlinear Kinetic Inductance

  1. Michael R. Vissers,
  2. Johannes Hubmayr,
  3. Martin Sandberg,
  4. Saptarshi Chaudhuri,
  5. Clint Bockstiegel,
  6. and Jiansong Gao
We have designed, fabricated and tested a frequency-tunable high-Q superconducting resonator made from a niobium titanium nitride film. The frequency tunability is achieved by injecting
a DC current through a current-directing circuit into the nonlinear inductor whose kinetic inductance is current-dependent. We have demonstrated continuous tuning of the resonance frequency in a 180 MHz frequency range around 4.5 GHz while maintaining the high internal quality factor Qi>180,000. This device may serve as a tunable filter and find applications in superconducting quantum computing and measurement. It also provides a useful tool to study the nonlinear response of a superconductor. In addition, it may be developed into techniques for measurement of the complex impedance of a superconductor at its transition temperature and for readout of transition-edge sensors.
arxiv pdf