Figure 4: Characteristics of a CBT immersed in 3He/4He refrigerant.
(a) Fitting to the warmest three measurements gives CΣ=209.5 fF and RT=23.21 kΩ. The fitted minimum electron temperatures 
for the warmest three curves are in reasonable agreement with the refrigerator temperatures as measured by the vibrating wire resonator (VWR) thermometer: 29.4, 19.0 and 10.5 mK, respectively. (b) Measured electron temperature in the CBT as the refrigerator cooled steadily from 10 to 2.7 mK over a period of 12 h. The solid curve shows a fit of the form 
, yielding an exponent x=2.7. The dot-dashed curve shows a best fit of 
. The dashed line shows Te=Tmxc. (c) The measured Te as the refrigerator was temporarily cooled in single-shot mode to 2.2 mK, reaching a lowest Te below 3.7 mK.
