S. Kubatkin

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

Fast tunable high Q-factor superconducting microwave resonators

  1. S. Mahashabde,
  2. E. Otto,
  3. D. Montemurro,
  4. S. de Graaf,
  5. S. Kubatkin,
  6. and A. Danilov
We present fast tunable superconducting microwave resonators fabricated from planar NbN on a sapphire substrate. The 3λ/4 wavelength resonators are tuning fork shaped and tuned by
passing a dc current which controls the kinetic inductance of the tuning fork prongs. The λ/4 section from the open end operates as an integrated impedance converter which creates a nearly perfect short for microwave currents at the dc terminal coupling points, thus preventing microwave energy leakage through the dc lines. We measure an internal quality factor Qint>105 over the entire tuning range. We demonstrate a tuning range of >3% and tuning response times as short as 20 ns for the maximum achievable detuning. Due to the quasi-fractal design, the resonators are resilient to magnetic fields of up to 0.5 T.
arxiv pdf