Modeling and scaling of ADR systems for next-generation millikelvin cooling for quantum computers

Quantum technologies, in particularly superconducting quantum computing, demand robust and scalable cooling solutions operating deep in the millikelvin regime. Adiabatic Demagnetization Refrigeration (ADR) offers a helium-3-free alternative with strong potential for modular scaling. Building on our previous demonstration of continuous ADR (cADR) operation below 30 mK in a compact rack-mounted system, the LEMON project advances the technology toward a larger-scale ADR platform targeting 20 µW at 20 mK—an order of magnitude improvement over the ~3 µW at 50 mK achieved in earlier systems. Achieving this performance requires a fundamental redesign of ADR components and a detailed understanding of their coupled behaviour. To this end, we have developed a comprehensive modeling framework that captures the full cADR cooling cycle, including refrigerants, mechanical and superconducting heat switches, and thermal interfaces between all components. The theoretical model has been experimentally validated using a dedicated cryogenic test platform providing the millikelvin environment and enabling systematic characterization of materials and prototype components. The combined simulation and experimental results provide new insight into materials properties, interface conductance, and switching dynamics, guiding the optimization of next-generation ADR systems. These advances establish a predictive and scalable foundation for magnetic refrigeration in large-scale quantum computing infrastructure.