TECHNOLOGICAL ASPECTS OF QUANTUM DECOHERENCEIN SUPERCONDUCTING JOSEPHSON QUBITS

Abstract

The aim of this thesis was to realize superconducting quantum bits by using novel fabrication techniques and materials in order to enhance the coherence time of the former devices. For the system to be studied we chose the ux-biased phase qubit, which consists of a Josephson junction integrated in a superconducting loop. This qubit realization has some advantages, which make it an ideal test-bed for different fabrication technologies and materials. Relatively large Josephson junctions can be used in the phase qubit realization, which are easy to be fabricated by using standard lithographic technology with the flexibility of employing various fabrication techniques and materials. The coherence of current-generation of superconducting qubits seems to be limited by intrinsic sources of noise and energy loss, related to materials' defects (two-level systems, TLSs) on the surfaces and interfaces of the superconducting lms, and in the bulk of the dielectric films used for the microelectronic realization of the circuits. For this reason, we aimed our research activities on the realization of low loss dielectrics (a-Si:H), on its integration with Josephson junction technologies, on the protection of the superconducting films' surfaces from unwanted contamination, and on the optimization of the circuit design and fabrication processes.