Cooling electrons from 1 K to 400 mK with V-based nanorefrigerators

The fabrication and operation of V-based superconducting nanorefrigerators is reported. Specifically, electrons in an Al island are cooled thanks to hot-quasiparticle extraction provided by tunnel-coupled V electrodes. Electronic temperature reduction down to 400 mK starting from 1 K is demonstrated with a cooling power ~20 pW at 1 K for a junction area of 0.3 micron^2. The present architecture extends to higher temperatures refrigeration based on tunneling between superconductors and paves the way to the implementation of a multi-stage on-chip cooling scheme operating from above 1 K down to the mK regime.