Feasibility of Coulomb blockade thermometry in metrology

Coulomb blockade thermometer (CBT) is a simple, magnetic-field-independent primary thermometer for everyday use at cryogenic temperatures. Its properties are well understood by now. The absolute accuracy at present is about ± 0.5%. Recently, we have started studying the possibility of using CBT in metrological applications. We have especially in mind the future extension of the international temperature scale below 0.65 K, which is the lower end of ITS-90. Experiments with arrays containing more than 100 tunnel junctions in series are in progress in order to decrease the effects of electromagnetic environment and of co-tunnelling even below the present level.