Dilution-equivalent solid-state chip refrigeration*

Cooling below 100 mK is an operative prerequisite in several quantum technology applications. It is typically achieved in expensive He3/He4 dilution refrigerators, where massive thermal payloads are cooled to very low temperatures over the course of tens of hours. Yet, in several quantum devices, only few miniaturized active elements are required to reach such low temperature levels.

Here we present a multi-stage thermionic cooler, targeting the 1.5K to 100 mK range. Its core concept consists in suspending silicon substrates with semiconductor-superconductor tunnel junctions, providing both phonon isolation and efficient electron cooling of chip-level payloads.

Compared to dilution refrigeration, our approach reduces sub-kelvin cooldown times to few seconds and benefits from intrinsically maintenance-free operation. Furthermore, the negligible system mass and footprint are optimally suited to compact turnkey systems and are especially ideal for space-borne applications.

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