A nanoelectronic chip cooled to the world record temperature of 2.8 mK
In an article1 published in Applied Physics Letters, a group of researchers from the University of Basel (Switzerland) led by Dominik Zumbühl tackled the cooling at very low temperatures of nanoelectronic devices, such as Coulomb blockade thermometers operating with very few electrons in the ballistic regime. Due to their very low thermal conductivity at low temperatures, nanoelectronic devices are highly sensitive to parasitic heat leaks and thus very difficult to cool.
According to the article, adiabatic demagnetisation of both the electric leads and the metallic “islands” of the chip itself solved this problem. “It reduces external heat leaks through the leads and provides on-chip refrigeration, together cooling the thermometer down to 2.8?±?0.1 mK.”
In other words, the researchers cooled all the electrical connections of the chip to a very low temperature (150 microkelvin). A second time, another cooling system was directly integrated in the chip itself, with a Coulomb blockade thermometer on it, which was also magnetically cooled to a temperature almost as low as absolute zero. The main limitation to lowering the temperature further stemmed from vibrations induced by the pulse-tube refrigerator pre-cooling the experiment.
1 PALMA, M. SCHELLER C. P. MARADAN D. On-and-off chip cooling of a Coulomb blockade thermometer down to 2.8?mK. Applied Physics Letters. 2017, vol. 111, issue 25. Available on http://aip.scitation.org/doi/full/10.1063/1.5002565 (Accessed 2018-02-13).
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