  We demonstrate quantum limited electronic refrigeration of a metallic island
in a low temperature micro-circuit. We show that matching the impedance of the
circuit enables refrigeration at a distance, of about 50 um in our case,
through superconducting leads with a cooling power determined by the quantum of
thermal conductance. In a reference sample with a mismatched circuit this
effect is absent. Our results are consistent with the concept of
electromagnetic heat transport. We observe and analyze the crossover between
electromagnetic and quasiparticle heat flux in a superconductor.
