Direct comparison of millikelvin primary electron thermometers and cryogenic low-pass filters

With the growing quantity and increasing complexity of millikelvin quantum electronics experiments, the ability to keep the effective temperature of electrons close to the temperature provided by a dilution refrigerator becomes ever more challenging. This requires the integration of robust low-pass filters, appropriate thermal anchoring, and radiation shielding, while it also increases the demand for accurate primary electron thermometers to be directly implemented in experimental setups. Here, we present a direct comparison of two established primary electron thermometers: Coulomb blockade thermometers (CBT) based on series of tunnel junctions between metallic islands [1], and normal-metal-insulator-superconductor (NIS) junctions [2]. Their operating principles are disparate, as aluminum is used as superconductor for the NIS but as normal metal for the CBT. We characterize both types of thermometers inside cryofree dilution refrigerators down to 10 mK base temperatures, measuring electron temperatures below 30 mK. We use these electron thermometry methods to investigate the influence of several types of low-pass filtering at different stages in the dilution refrigerator.

1. O. Hahtela et al., Metrologia 54, 69-76 (2017)

2. A.V. Feshchenko et al., Phys. Rev. Appl. 4, 034001 (2015)