Biepitaxial Josephson junctions and superconducting field effect transistors (SuFET) were fabricated in order to combine both techniques to a Josephson junction field effect transistor (JoFET). The Josephson junctions show RSJ-like behaviour. At 30 K a critical current density of J, = lo4 A/cm2 and an LRN-product of 0.1 mV were obtained. The oscillation of Shapiro steps with applied microwave f...

Quasiparticle tunneling across a Josephson junction sets a limit for the lifetime of a superconducting qubit state. We develop a general theory of the corresponding decay rate in a qubit controlled by a magnetic flux. The flux affects quasiparticles tunneling amplitudes, thus making the decay rate flux-dependent. The theory is applicable for an arbitrary quasiparticle distribution. It provides ...

We measure the high-frequency emission of a single Cooper pair transistor (SCPT) in the regime where transport is only due to tunneling of Cooper pairs. This is achieved by coupling on chip the SCPT to a superconductor-insulator-superconductor junction and by measuring the photon assisted tunneling current of quasiparticles across the junction. This technique allows a direct detection of the ac...

We have measured the current-voltage characteristics of small-capacitance single Josephson junctions at low temperatures ( T< or =0.04 K), where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. We have clearly observed Coulomb blockade of Cooper-pair tunneling and even a region of negative diffe...

We calculate the electrical currents through a superconductor-insulator-superconductor junction which is also weakly coupled to a normal-metal side probe. The voltage V applied to the normal-metal terminal controls the occupation of Andreev energy levels En , and therefore controls the Josephson current flowing through these levels. Whenever the probe voltage crosses an Andreev level, the Josep...