Characterization of Superconducting resonators for qubit applications

Superconducting resonators are a key building block for the implementations of several qubit architectures. In circuit-Quantum-Electro-Dynamics (cQED) its fundamental role is to provide a bus for the quantum information to be distributed and retrieved from the qubits.

Characterization of Superconducting resonators is of fundamental importance also for qubits optimization as the two systems share the same sources of de-coherence.

The main challenges associated to the development of low-loss superconducting resonators originate from the control over three main mechanisms of photon de-coherence namely quasi-particle generation, radiation losses and coupling to Two-Level-Systems (TLS). Whereas for the first two mechanisms one can rely on a careful choice over proper shielding and chip housing, limiting the coupling to stray infrared light and box modes, the ubiquitous photon coupling to the external world mediated by TLSs is the main challenge for the fabrication of devices with superior performances and reproducibility.

The aim of this master thesis is to characterize  
several types of resonator devices, either in the distributed geometry (Co-Planar-Waveguide) or in the Lumped-Element geometry and for several superconducting materials. The intrinsic quality factors of all the resonators will give a measure of the quality of the films and their relationship with their physical properties. These measurements, complemented by finite-element analysis of several resonator geometries, will give information about the participation ratios of the different interfaces and  their loss-tangents ultimately suggesting the best choices in terms of material selection and integration pathways.

For this master thesis, a good knowledge of physics and material science is required. Knowledge over superconductivity and basic understanding of microwave techniques is highly appreciated. The student is expected to interact with different researchers focusing on aspects related to thin-film and device integration in our world-class 300mm cleanroom.