  Refrigeration is an important enabler for quantum technology. The very low
energy of the fundamental excitations typically utilized in quantum technology
devices and systems requires temperature well below 1 K. Expensive cryostats
are utilized in reaching sub-1 K regime and solid-state cooling solutions would
revolutionize the field. New electronic micro-coolers based on phonon-blocked
semiconductor-superconductor junctions could provide a viable route to such
miniaturization. Here, we investigate the performance limits of these junction
refrigerators.
