The goal of the project is to optimize and fabricate microwave circuitry for two tone spectroscopy measurement of novel superconducting Josephson junctions. The junctions in question here are unique in their own right; superconductor-semiconductor-superconductor junctions based on planar strained Germanium, with a highly anisotropic spin orbit interaction. Bringing them in close contact to a superconductor and making a Josephson junction with them makes something called “Andreev Bound States” (ABS), which we are here to study. ABS in these specialized semiconductor quantum wells give rise to interesting current phase relations, which can be tuned using a top gate. Gaining control over these allows us to tailor the behavior of the junction, and later use them to our advantage for superconducting qubits. The project focusses on developing and building the circuitry for the microwave readout. We will be working with coplanar waveguide (CPW) feedlines and resonators, which we strongly couple with the system housing the bound states.

We will be using superconducting resonators for identifying the bound states using spectroscopic measurements in the 3-10 GHz range. Building magnetic field compatible coplanar waveguide and lumped element resonators requires excellent film quality with a low sheet resistance and a high critical field. All the fabrication will be done in the Helmholtz Nano Facility (HNF) in Forschungszentrum Jülich using our dedicated specialized thin film deposition tool, in HNF’s ISO1-3 cleanroom facility for device fabrication. It is equipped with all the resources one would need for fabrication and characterization of nanoscale devices.

Your Task

You will be using our thin film deposition tool to optimize NbTiN superconducting films to obtain the best temperature and field performance needed for obtaining high contrast two tone spectroscopy measurements for our Josephson junctions. You will be operating the tool independently to make superconducting thin films suited for the multitudes of our processes. You will gain cleanroom training and will be handling the fabrication line for resonators. Workplace for this part of the project will be Forschungszentrum Jülich.

Apart from the fabrication, the project will involve doing cryogenic temperature dependent four-point sheet resistance, X ray diffraction measurements and high frequency network analysis with the responsible PhD student. The later part of the project will consist of a full workup of the fabricated resonators in our Adiabatic Demagnetization Refrigerator and our Dilution Refrigerator equipped with a 9-1-1 T vector magnet in Aachen. We will be doing magnetic field sweeps to characterize multiple designs in different possible field configurations.

What we offer

  • Workplace, laptop for duration of the project.
  • An equivalent student assistant contract via Forschungszentrum Jülich
  • Young, international, dynamical workplace, located on Campus Melaten (Campus Boulevard 79)
  • Exposure to leading research activities in quantum technology