Heat leaks and noise in microkelvin electronics on a pulse-tube cryostat*

On-chip microkelvin temperatures hold the potential to explore new physics with small energy scales such as novel quantum states and would open the door to unprecedented quantum coherence. In this work, we use on-and-off chip adiabatic nuclear refrigeration on a pulse-tube cryostat to cool metallic coulomb blockade thermometers deep into the microkelvin regime. We obtain temperatures as low as 224±7 μK, remaining below 300 μK for 27 hours [Samani et al. arXiv:2110.06293 (2021)], thus providing sufficient time for measurements. Dry dilution refrigerators have grown enormously in popularity due to their vast experimental space and independence of helium, but their unavoidable vibrations are making microkelvin cooling very difficult. Here, we investigate the heat leak onto a Coulomb blockade thermometer as a function of the external magnetic field. Furthermore, the role of electronic noise is explored, which is limiting the current temperature reading. Finally, we propose improvements allowing to cool below 50 μK for a new generation of microkelvin experiments.