UHF-resistive SQUID noise thermometer at temperatures between 0.005 and 4.2K

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Abstract
The RF SQUID noise thermometer is a convenient instrument to directly measure thermodynamic temperatures below 4.2K. However, as the uncertainty is statistically related to the number of frequency counts, it requires long measurement times. The authors describe a thermometer in which the time for one frequency measurement is reduced by using a 320 MHz-SQUID to improve the signal-to-noise ratio; making period measurements to avoid the round off errors; and using a fast computer to keep the processing time for a single measurement below 2 ms. The direct reading resolution of the noise thermometer is 1% for a total measuring time of 1 min, or less in longer time intervals. This time can be further reduced for relative temperature measurements by utilising the simultaneously available noise resistance information.