Regensburg 2019 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 28: Cryotechnique: Refrigeration and Thermometry

TT 28.3: Vortrag

Dienstag, 2. April 2019, 11:45–12:00, H23

Cross Correlated Noise Thermometer for Milli-Kelvin Temperatures — •Christian Ständer, Andreas Reifenberger, Felix Mücke, Marius Hempel, Sebastian Kempf, Andreas Reiser, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institute for Physics, Heidelberg University.

Within our search for easy-to-use and reliable thermometers for milli-Kelvin and micro-Kelvin temperatures we developed a noise thermometer, where the Johnson noise of a massive cylinder of high purity silver is monitored simultaneously by two current sensing dc-SQUIDs. Operating both SQUIDs in voltage biased mode in a 2-stage configurations allows to reduce the power dissipation as well as the noise of the SQUIDs to a minimum. By cross-correlating the two SQUID signals, the noise contribution of the read-out electronics is suppressed to a marginal level even at micro-Kelvin temperatures. To further reduce the correlated amplifier noise we fabricated SQUIDs with minimal coupling of input and feedback coil. We compare two thermometers of this type to each other within the temperature range from 1 K down to 5 mK. Statistical uncertainties below 0.25 % are achieved within 10 s of measurement time. No significant systematic deviation between the two thermometers was observable. According to readout noise and a detailed thermal model the thermometers could be used down to 0.5 µ K.