From quantum metrology to applications

It is important that measurements produce predictable and reproducible results irrespective of time and location. This is enabled by the International System of Units (SI), which is realized through primary standards: devices that can either measure or produce a known value of a quantity without calibration against any other standard for quantity of the same kind. This thesis explores quantum standards for the ampere and the kelvin, and devices that are byproducts of this research or enablers for the devices spawning from it. Coulomb blockade thermometer (CBT) was investigated as a possible realization of the kelvin at low temperatures. We constructed a setup, where temperature could be determined through Boltzmann constant and traceable voltage measurements. The CBT was also compared to the PLTS-2000 temperature scale and to two other Boltzmann constant based primary thermometers. Two different quantum phenomena were studied in the context of the ampere: single-electron tunneling in superconductor -- insulator -- normal metal (NIS) junctions and quantum phase slips (QPS) in superconducting nanowires. We observed QPS in novel material: molybdenium silicide (MoSi). It has been theoretically predicted that high normal state resistivity would be beneficial for the QPS based current standard. This resistivity can be achieved in MoSi. Since the novel standards for the ampere would produce relatively small currents (up to nanoampere), low frequency noise can increase the measurement times from hours to weeks. On the other hand, high frequency noise can initiate unwanted tunnelings and degrade the accuracy of devices. The low frequency noise problems were tackled by proper cabling and two filters were characterized in the high frequency range by NIS based detectors. Finally we utilized the understanding of NIS systems, based on research aiming at realization of the quantum current standard, in two other applications: noise detectors and coolers. We demonstrated NIS-based cooling of a mm-scale object by silicon-aluminium junctions. The cooling was enabled by phonon transmission bottleneck. We also analyzed by simulations that electric cooling from 1.5 K to 100 mK is a realistic goal.