SUPERCONDUCTING QUANTUM CIRCUITS

Abstract

This thesis describes a number of experiments with superconducting cir- cuits containing small Josephson junctions. The circuits are made out of aluminum islands which are interconnected with a very thin insulating alu- minum oxide layer. The connections form a Josephson junction. The current trough the junction is related to the superconducting phase difference across the junction and described by the well-known Josephson relation. The char- acteristic energy scale for this effect is the Josephson energy, which is a measure for the strength of the coupling of the islands. Due to the parallel plate geometry of the junction a capacitance is formed. This capacitance leads to a charging effect. The characteristic energy scale for this effect is given by the charging energy. With the shadow evaporation technique it is possible to make the Josephson junction area very small and the two characteristic energy scales of the same order of magnitude. Charge and phase are conju- gate variables. Therefore a circuit containing such small Josephson junctions exhibits quantum effects. The microfabrication technique used in this the- sis allows fabrication of solid circuits with controlled quantum mechanical behavior.