Josephson-effect absolute noise thermometer: Resolution of unmodeled errors

Abstract
An absolute cryogenic temperature scale is being defined at the National Bureau of Standards using the linewidth of radiation emitted by a resistively shunted Josephson junction. We report careful measurements of the impedance of this noise thermometer and show that its behavior is in excellent agreement with the predictions of the resistively shunted junction model assuming a sinusoidal current‐phase relationship. The implications for absolute noise thermometry are discussed.