How cold can you get in space? Quantum physics at cryogenic temperatures in space

Although it is often believed that the coldness of space is ideally suited for performing measurements at cryogenic temperatures, this must be regarded with caution for two reasons: firstly, the sensitive instrument must be completely shielded from the strong solar radiation and therefore, e.g., either be placed inside a satellite or externally on the satellite's shaded side. Secondly, any platform hosting such an experiment in space generally provides an environment close to room temperature for the accommodated equipment. To obtain cryogenic temperatures without active cooling, one must isolate the instrument from radiative and conductive heat exchange with the platform as well as possible. We perform analyses on the limits of this passive cooling method for a recently proposed experiment to observe the decoherence of quantum superpositions of massive objects. In this context, we obtain temperatures of 27 K for the optical bench and 16 K for the critical experimental volume. Our analyses and conclusions can readily be applied to similar science experiments requiring a cryogenic environment in space.