Thermal transport in devices cooled below 10 millikelvin by on-chip demagnetisation

Significant progress has recently been made using the magnetic refrigeration of material deposited on-chip to cool the electrons in micro- and nanoelectronic devices into the sub-mK regime [1,2,3]. This provides a low-investment technique for going beyond the off-chip temperatures provided by dilution fridges. Achieving sub-millikelvin electron temperatures reduces noise and enhances sensitivity for observing known and new physical phenomena, in turn improving the performance of quantum technologies, sensors and metrological standards. Typically, off-chip cooling below 10 mK cooling is limited by weak electron-phonon coupling, set against the heat leak in the electronic system from measurement leads and the environment. Here we report on our work to understand the relative importance of cooling on-chip and off-chip components and the thermal subsystem dynamics [4]. We measure and simulate the behaviour of a Coulomb blockade thermometer with on-chip copper refrigerant. Our model can be used to optimise the design and measurement of devices which exploit these cooling techniques.

1. Sarsby et al., Nature Communications 11, 1492 (2020)

2. Jones et al., Journal of Low Temperature Physics 201, 772 (2020)

3. Samani et al., Phy. Rev. Research 4, 033225 (2022)

4. Autti et al., arXiv:2209.07099 (2022)