Cooling nanoelectronic devices below 10 mK is a great challenge since thermal conductivities become very small, thus creating a pronounced sensitivity to heat leaks. Here, we overcome these difficulties by using adiabatic demagnetization of both the electronic leads and the large metallic islands of a Coulomb blockade thermometer. This reduces the external heat leak through the leads and also provides on-chip refrigeration, together cooling the thermometer down to 2.8 ± 0.1 mK. We present a thermal model which gives a good qualitative account and suggests that the main limitation is heating due to pulse tube vibrations. With better decoupling, temperatures below 1 mK should be within reach, thus opening the door for μK nanoelectronics.
This corresponds to a nuclear polarization of ≈40% in the Cu plates and ≈17% in the CBT islands.17
Static heat leak: 32 aW per CBT junction, corresponding to 5.4 nW/mol Cu, compared to typically 1–2 nW/mol Cu for the large plates. Dynamic heat leak: 485 aW per junction during AND, corresponding to 82 nW/mol Cu, compared to an estimated 30 nW/mol Cu for the large plates.25