Superconducting quasiparticle traps for CPW resonators

Excess quasiparticles limit the quality factor of the superconducting resonators by presenting an ohmic path for energy dissipation. It has been shown that normal metal in contact with the superconductor can act as a quasiparticle trap by confining quasiparticles away from the superconductor. Similarly, a small band gap superconductor in contact with a larger band gap superconductor can also act as a quasiparticle trap by confining quasiparticles away from the larger bandgap superconductor into the smaller one.
Here aluminum (Al) and titanium nitride (TiN) are used as two superconductors. Finite difference method (FDM) simulations of the coupled phonon and quasiparticle systems of both superconductors suggest that the quasiparticle traps on the ground plane may be effective for setback distances less than 200 µm away from TiN waveguide features. Experimentally, a thin layer of Al is grown in-situ on TiN using molecular beam epitaxy (MBE) with a negligible dielectric layer between the two superconductors to increase the trapping efficiency of the Al. Currently work focuses on fabricating quarter wavelength resonators in TiN with different setbacks of the Al trap. The optimum setback of Al from the active region of the TiN resonator will be explored.