Kaveh Delfanazari

Robust NbN on Si-SiGe hybrid superconducting-semiconducting microwave quantum circuit

  1. Paniz Foshat,
  2. Samane Kalhor,
  3. Shima Poorgholam-khanjari,
  4. Douglas Paul,
  5. Martin Weides,
  6. and Kaveh Delfanazari
Advancing large-scale quantum computing requires superconducting circuits that combine long coherence times with compatibility with semiconductor technology. We investigate niobium
nitride (NbN) coplanar waveguide resonators integrated with Si/SiGe quantum wells, creating a hybrid platform designed for CMOS-compatible quantum hardware. Using temperature-dependent microwave spectroscopy in the single-photon regime, we examine resonance frequency and quality factor variations to probe the underlying loss mechanisms. Our analysis identifies the roles of two-level systems, quasiparticles, and scattering processes, and connects these losses to wafer properties and fabrication methods. The devices demonstrate reproducible performance and stable operation maintained for over two years, highlighting their robustness. These results provide design guidelines for developing low-loss, CMOS-compatible superconducting circuits and support progress toward resilient, scalable architectures for quantum information processing.
arxiv pdf

Quasiparticle Dynamics in NbN Superconducting Microwave Resonators at Single Photon Regime

  1. Paniz Foshat,
  2. Shima Poorgholam-khanjari,
  3. Valentino Seferai,
  4. Hua Feng,
  5. Susan Johny,
  6. Oleg A. Mukhanov,
  7. Matthew Hutchings,
  8. Robert H. Hadfield,
  9. Martin Weides,
  10. and Kaveh Delfanazari
Exchanging energy below the superconducting gap introduces quasiparticle energy distributions in superconducting quantum circuits, which will be responsible for their decoherence. This
study examines the impact of quasiparticle energy on the performance of NbN superconducting microwave coplanar waveguide resonators on silicon chips. We measured the resonance frequency and internal quality factor in response to temperature sweeps to evaluate the effect of quasiparticle dynamics. Moreover, by calculating the complex conductivity of the NbN film, we identified the contribution of quasiparticle density to the experimental results.
arxiv pdf