Josephson junction devices and detectors based on incoherent Cooper pair tunneling

This thesis deals with the physics of small superconducting circuits with dimensions of the order of one hundred nanometers. Accordingly, the work belongs to a field of research called nanophysics or nanoelectronics. The effects we study rely on phenomena such as superconductivity and the control of single electrons in nanostructures. Practically, this means that we are looking at quantum mechanical effects at very small energies, which requires the cooling of samples to well below 1 degree Kelvin in order to observe the effects. The aim is to study the basic physics of superconducting devices and investigate how they can be used in nanoelectronic devices and detectors. The basic component in the studied devices is the small Josephson junction, which is a superconducting tunnel junction, that allows the charge carriers of superconductivity, the so called Cooper pairs, to tunnel across an insulating barrier. The tunneling of particles over a classically forbidden zone is a pure quantum mechanical effect. In this thesis, we use the Josephson junction for experiments in energy level spectroscopy, namely, to study the quantized energy levels of a another Josephson junction, or rather a SQUID (superconducting quantum interference device) connected to the detector junction. With an external magnetic flux, we could change the quantum mechanical behavior of the SQUID from a simple harmonic oscillator to an energy band, thus, giving another direct evidence of the existence of the energy bands. We employed a Josephson junction as a highly sensitive detector of shot noise, generated by another tunnel junction. Therefore, we demonstrated a new way to measure asymmetric noise due to the discreteness of charge carriers. The characterization of noise is essential in applications, especially involving quantum bits and quantum computation. Our method shows good potential for future experiments for studying noise in various nanostructures. Finally, a new kind of nanodevice, the Bloch oscillating transistor (BOT), which is based on a Josephson junction circuit, was developed and characterized. The BOT is shown to have a very low noise temperature and considerable current and power gain, thus making it a promising on-chip current amplifier for nanoelectronics.reviewe