Superconducting Quantum Refrigerator: Breaking and Rejoining Cooper Pairs with Magnetic Field Cycles

We propose a solid-state refrigeration technique based on repeated adiabatic magnetization and demagnetization cycles of a superconductor, which acts as the working substance. The gradual cooling down of a substrate (normal metal) in contact with the working substance is demonstrated for different initial temperatures of the substrate. Excess heat is given to a hot large-gap superconductor. The on-chip refrigerator works in a cyclic manner because of an effective thermal switching mechanism: heat transport between N-N versus N-S junctions is asymmetric because of the appearance of the energy gap. This switch permits selective cooling of the metal. We find that this refrigeration technique can cool down a 0.3 cm(3) block of Cu by almost 2 orders of magnitude starting from 200 mK, and down to about 1 mK starting from the base temperature of a dilution fridge (10 mK). The corresponding cooling power at 200 and 10 mK for a 1 x 1 cm(2) interface are 25 and 0.06 nW respectively, which scales with the area of the interface.