Noise thermometry at low temperatures: MFFT measurements between 1.6 K and 1 mK

Reliable and traceable thermometry is a demanding task at low temperatures. Recently, we have developed a dc SQUID-based noise thermometer, the magnetic field fluctuation thermometer (MFFT), for practical thermometry in the low temperature range [1]. Its operational principle is based on the Nyquist theorem ensuring a linear characteristic over a wide range of temperatures. This makes the MFFT capable to replace a variety of secondary thermometers, which are normally used in the low temperature range. For the first time, we report on MFFT measurements over more than 3 decades in temperature from about 1.6 K down to below 1 mK The deviations from a high-accuracy realization of the PLTS-2000 are found to be ≍ 1%.