Characterization of Josephson junction devices for qubit applications

Josephson junctions (JJ) are the working horse for any superconducting qubit realization. They typically come in the form of a thin insulating layer sandwiched between two superconductors. The JJ are the essential ingredient for the formation of an addressable two-level system, the qubit, thanks to their non-linear inductance and to the possibility of tuning the energy levels by an external applied magnetic field.     

For its ease of processing, Aluminum has been the material of choice due also to the availability of a stable and controllable oxide.

Despite poor control over film quality, JJs fabricated from thermal diffusion of oxygen into aluminum represent the current adopted method for the fabrication of reliable tunnel junctions targeting qubit devices. This process can furnish qubit devices with sufficient predictability in terms of frequency of operation and with characteristic lifetimes exceeding tens of microseconds.  

The above-mentioned approach, although reliable for the exploration of qubit device prototypes, is based on processes which are not compatible with the integration of large arrays of qubits necessary for the implementation of error-correcting protocols.

It is then necessary to develop a robust, scalable and versatile platform able to integrate and characterize JJs devices compliant with stricter industry standards.

In this master thesis the student will characterize Josephson junction devices issued from our industry-standard cleanroom, aiming at the extraction of their relevant parameters like critical current and sub-gap resistances.

Specific tasks include the improvement of the characterization techniques, development of a low-noise setup and interpretation of the data.

For this master thesis, a good knowledge of physics and basic understanding of superconducting devices is required. Knowledge over python programming is highly appreciated.