A SQUID-based primary noise thermometer for lowtemperature metrology

Abstract

Practical temperature measurements in accordance with the international system of units require traceability to the international temperature scales currently in force. Along with the awaited redefinition of the unit of temperature, the kelvin, on the basis of the Boltzmann constant, in future its mise en pratique will allow the use of approved methods of primary thermometry for the realization and dissemination of the kelvin. To support this process, we have developed a DC superconducting quantum interference devicebased noise thermometer especially designed for measurements of thermodynamic temperature in a broad temperature range from 5K down to below 1mK. In this paper, we describe in detail the primary magnetic field fluctuation thermometer and the underlying model applied for the temperature determination. Experimental measurement results are presented for a comparison with the Provisional Low Temperature Scale 2000 between 0.7K and 16mK including an uncertainty budget for the measured thermodynamic temperatures. In this setup, the relative combined standard uncertainty is equal to 0.6%.