Regensburg 2016 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 20: Cryotechnique & Measuring Devices: Poster Session

TT 20.3: Poster

Montag, 7. März 2016, 15:00–18:00, Poster D

Current Sensing Noise Thermometer with Cross Correlated Readout for Milli-Kelvin Temperatures — •Felix Mücke, Andreas Reifenberger, Marius Hempel, Sebastian Kempf, Andreas Reiser, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institut für Physik, INF 227, Universität Heidelberg, 69120 Heidelberg

Within our search for easy-to-use reliable thermometers for milli-Kelvin and micro-Kelvin temperatures we recently developed a noise thermometer, where the Johnson current noise of a massive cylinder of high purity silver is monitored simultaniously by two current sensing dc-SQUIDs. The Si-Chip carrying the two SQUIDS is glued directly onto the noise source. Operating both SQUIDS in voltage biased mode in 2-stage SQUID configurations allows to reduce the power dissipation as well as the noise of the SQUIDS to a minimum. By computing the cross-correlation of the two SQUID signals the noise contribution of the read-out is suppressed to a level which is marginal even at micro-Kelvin temperatures. We present the thermometer design and discuss the results of experimental tests, where we compared the thermometer to a previously developed magnetic field fluctuation thermometer in the temperature range from 2.5 K down to 9 mK. Statistical uncertainties below 0.5 % are achieved within 10 s of measurement time. Within this uncertainty no self heating was observable at base temperature. This agrees with expectations from the thermal model of the thermometer, which suggests that self heating should be marginal even at temperatures well below 1 mK.