Characterizing cryogenic amplifiers with a matched temperature-variable noise source

  1. Slawomir Simbierowicz,
  2. Visa Vesterinen,
  3. Joshua Milem,
  4. Aleksi Lintunen,
  5. Mika Oksanen,
  6. Leif Roschier,
  7. Leif Grönberg,
  8. Juha Hassel,
  9. David Gunnarsson,
  10. and Russell E. Lake
We present a cryogenic microwave noise source with characteristic impedance of 50 Ω that can be installed in a coaxial line of a cryostat. The bath temperature of the noise source is continuously variable between 0.1 K and 5 K without causing significant back-action heating on the sample space. As a proof-of-concept experiment, we perform Y-factor measurements of an amplifier cascade that includes a traveling wave parametric amplifier and a commercial high electron mobility transistor amplifier. We observe system noise temperatures as low as 680+20−200 mK at 5.7 GHz corresponding to 1.5+0.1−0.7 excess photons. The system we present has immediate applications in the validation of solid-state qubit readout lines.
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