Dresden 2020 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 60: Cryotechnique: Refrigeration and Thermometry

TT 60.4: Talk

Thursday, March 19, 2020, 15:45–16:00, HSZ 103

Cross Correlated Noise Thermometer for Milli-Kelvin Temperatures — •Christian Ständer, 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 designed and fabricated SQUIDs with minimal coupling of input and feedback coil. We recently assembled a first small series of such thermometers to best reliability, reproducibility and user friendliness at beta-testing sites. In the complete investigated temperature range from 4 K down to 5 mK, the measured noisepower is linear in temperature. Statistical uncertainty below 0.1% is achieved within integration times of 45 s. The thermometers of the series agree within less than 0.1% in the complete temperature range.