S. Kern

Third harmonic-mediated amplification in TWPA

  1. E. Rizvanov,
  2. S. Kern,
  3. P. Neilinger,
  4. and M. Grajcar
In Josephson Traveling-Wave Parametric Amplifiers, higher-order harmonics of the pump tone and its sidebands are commonly present and typically regarded as parasitic. Consequently,
most design efforts have focused on suppressing these harmonics. In spite of that, motivated by transient simulations, we extend the coupled-mode theory and demonstrate that, contrary to conventional belief, the third harmonic can enhance amplifier performance, improving both gain and bandwidth. We show that the recently developed plasma oscillation-based amplifier is particularly well-suited for exploiting this effect. Their dispersion relation enables us to observe the phenomenon in transient numerical simulations using JoSIM and WRspice. These simulations reveal improvement of the amplifier’s performance, specifically the doubling of the bandwidth and an increase in the gain.
arxiv pdf

The transition regime between traveling-wave and resonant parametric amplifier

  1. S. Kern,
  2. P. Neilinger,
  3. E. Il'ichev,
  4. A. Sultanov,
  5. M. Schmelz,
  6. S. Linzen,
  7. J. Kunert,
  8. G. Oelsner,
  9. R. Stolz,
  10. A. Danilov,
  11. S. Mahashabde,
  12. A. Jayaraman,
  13. V. Antonov,
  14. S. Kubatkin,
  15. and M. Grajcar
Traveling wave parametric amplifiers based on kinetic or Josephson nonlinear inductance are known to be microwave quantum limited amplifiers. Usually, a perfectly impedance-matched
model is used to describe their characteristics in terms of standard coupled mode theory. In practice, the amplifiers are unmatched nonlinear devices with finite length, exhibiting ripples in the transmission. Since commonly used models fail to describe the ripples of real parametric amplifiers, here we are introducing a theoretical approach with non-negligible reflections, which provides their gain and bandwidth properly for both 3-wave and 4-wave mixing. Predictions of the model are experimentally demonstrated on two types of TWPA, based on coplanar waveguides with a central wire consisting of i) high kinetic inductance superconductor, and ii) array of 2000 Josephson junctions.
arxiv pdf