A cyclic superconducting quantum refrigerator for adiabatic magnetization cooling*

We propose a solid-state refrigeration technique using adiabatic magnetization/ demagnetization cycles of a superconductor, acting as the working substance. The gradual cooling down of a substrate (normal metal) in contact with the working substance is predicted, where the excess heat is given to a hot, large-gap superconductor. The selective cooling of the normal metal is due to an effective thermal switching mechanism owing to the asymmetry of heat transport between N/N versus N/S junctions. We predict cooling of a 0.3cm^3 block of Cu by almost two orders of magnitude starting from 200mK, and down to about 1mK starting from the base temperature of a dilution fridge (10mK). The cooling powers at 200mK and 10mK for a 1cmx1cm interface are 25 nW and 0.06 nW respectively, which scales with the area of the interface.