Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

TT 23: Solids At Low Temperature: Cryogenics

TT 23.5: Talk

Wednesday, March 29, 2006, 15:45–16:00, HSZ 02

Thermally robust noise thermometer for milli-kelvin temperatures — •Astrid Netsch, Elena Hassinger, Christian Enss, and Andreas Fleischmann — Kirchhoff-Institut fuer Physik, Universitaet Heidelberg, INF 227, D-69210 Heidelberg, Germany

The temperature dependence of thermally driven voltage fluctuations of an electrical resistor is described by the dissipation-fluctuation theorem. This fundamental law of statistical physics provides a direct relation between temperature and independently measurable quantities, making the measurement of noise an attractive option for primary thermometry. However, the realization of such thermometers for the measurement of very low temperatures has often been problematic, preventing this technique from being widely used in low temperature laboratories. We present a setup for Johnson-noise thermometry that uses a commercial dc-SQUID as preamplifier. The noise to be measured is generated by the thermal motion of electrons in a bulk sample of a high purity metal such as gold or copper. These random currents cause fluctuations of magnetic flux in a pickup coil which is connected to the input coil of a current-sensor dc-SQUID. The thermometer is easy to fabricate and rather insensitive to typical sources of parasitic heating. We discuss general design considerations as well as the dependence of the temperature uncertainty upon measurement time. To characterize the thermometer we compared it to a superconducting standard reference device (SRD1000) which represents the temperature scale PLTS-2000. The spectral power density of flux noise was measured as a function of temperature and found to be linear in the investigated range from 6 mK to 4 K.