Maxwell Drimmer

The effect of niobium thin film structure on losses in superconducting circuits

  1. Maxwell Drimmer,
  2. Sjoerd Telkamp,
  3. Felix L. Fischer,
  4. Ines C. Rodrigues,
  5. Clemens Todt,
  6. Filip Krizek,
  7. Dominik Kriegner,
  8. Christoph Müller,
  9. Werner Wegscheider,
  10. and Yiwen Chu
The performance of superconducting microwave circuits is strongly influenced by the material properties of the superconducting film and substrate. While progress has been made in understanding
the importance of surface preparation and the effect of surface oxides, the complex effect of superconductor film structure on microwave losses is not yet fully understood. In this study, we investigate the microwave properties of niobium resonators with different crystalline properties and related surface topographies. We analyze a series of magnetron sputtered films in which the Nb crystal orientation and surface topography are changed by varying the substrate temperatures between room temperature and 975 K. The lowest-loss resonators that we measure have quality factors of over one million at single-photon powers, among the best ever recorded using the Nb on sapphire platform. We observe the highest quality factors in films grown at an intermediate temperature regime of the growth series (550 K) where the films display both preferential ordering of the crystal domains and low surface roughness. Furthermore, we analyze the temperature-dependent behavior of our resonators to learn about how the quasiparticle density in the Nb film is affected by the niobium crystal structure and the presence of grain boundaries. Our results stress the connection between the crystal structure of superconducting films and the loss mechanisms suffered by the resonators and demonstrate that even a moderate change in temperature during thin film deposition can significantly affect the resulting quality factors.
arxiv pdf

Quasiparticle dynamics in a superconducting qubit irradiated by a localized infrared source

  1. Rodrigo Benevides,
  2. Maxwell Drimmer,
  3. Giacomo Bisson,
  4. Francesco Adinolfi,
  5. Uwe von Lüpke,
  6. Hugo Michiel Doeleman,
  7. Gianluigi Catelani,
  8. and Yiwen Chu
A known source of decoherence in superconducting qubits is the presence of broken Cooper pairs, or quasiparticles. These can be generated by high-energy radiation, either present in
the environment or purposefully introduced, as in the case of some hybrid quantum devices. Here, we systematically study the properties of a transmon qubit under illumination by focused infrared radiation with various powers, durations, and spatial locations. Despite the high energy of incident photons, our observations agree well with a model of low-energy quasiparticle dynamics dominated by trapping. This technique can be used for understanding and potentially mitigating the effects of high-energy radiation on superconducting circuits with a variety of geometries and materials.
arxiv pdf