Mikrokelvin electronics on a pulse-tube cryostat with a gate Coulomb blockade thermometer*

Access to lower temperatures has consistently enabled scientific breakthroughs. On-chip microkelvin temperatures would open the door to unprecedented quantum coherence, novel quantum states of matter, and also the discovery of unexpected phenomena. Adiabatic demagnetization is the workhorse of microkelvin cooling, requiring a dilution refrigerator precooling stage. Pulse-tube 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. On-chip thermometry in this unexplored territory is also not a trivial task due to extreme sensitivity to noise and heat leaks. Here, we present a pulse-tube compatible microkelvin sample holder with on-board cooling and microwave filtering and introduce a new type of temperature sensor, the gate Coulomb blockade thermometer, working deep into the microkelvin regime. Using on- and off-chip cooling, we demonstrate electronic 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.