F. Valenti

Superconducting granular aluminum resonators resilient to magnetic fields up to 1 Tesla

  1. K. Borisov,
  2. D. Rieger,
  3. P. Winkel,
  4. F. Hernandez,
  5. F. Valenti,
  6. A. Ionita,
  7. M. Wessbecher,
  8. M. Spiecker,
  9. D. Gusenkova,
  10. I. M. Pop,
  11. and W. Wernsdorfer
High kinetic inductance materials constitute a valuable resource for superconducting quantum circuits and hybrid architectures. Superconducting granular aluminum (grAl) reaches kinetic
sheet inductances in the nH/□ range, with proven applicability in superconducting quantum bits and microwave detectors. Here we show that the single photon internal quality factor Qi of grAl microwave resonators exceeds 105 in magnetic fields up to 1T, aligned in-plane to the grAl films. Small perpendicular magnetic fields, in the range of 0.5mT, enhance Qi by approximately 15%, possibly due to the introduction of quasiparticle traps in the form of fluxons. Further increasing the perpendicular field deteriorates the resonators‘ quality factor. These results open the door for the use of high kinetic inductance grAl structures in circuit quantum electrodynamics and hybrid architectures with magnetic field requirements.
arxiv pdf

Circuit Quantum Electrodynamics of Granular Aluminum Resonators

  1. N. Maleeva,
  2. L. Grünhaupt,
  3. T. Klein,
  4. F. Levy-Bertrand,
  5. O. Dupré,
  6. M. Calvo,
  7. F. Valenti,
  8. P. Winkel,
  9. F. Friedrich,
  10. W. Wernsdorfer,
  11. A. V. Ustinov,
  12. H. Rotzinger,
  13. A. Monfardini,
  14. M. V. Fistul,
  15. and I. M. Pop
The introduction of crystalline defects or dopants can give rise to so-called „dirty superconductors“, characterized by reduced coherence length and quasiparticle mean free
path. In particular, granular superconductors such as Granular Aluminum (GrAl), consisting of remarkably uniform grains connected by Josephson contacts have attracted interest since the sixties thanks to their rich phase diagram and practical advantages, like increased critical temperature, critical field, and kinetic inductance. Here we report the measurement and modeling of circuit quantum electrodynamics properties of GrAl microwave resonators in a wide frequency range, up to the spectral superconducting gap. Interestingly, we observe self-Kerr coefficients ranging from 10−2 Hz to 105 Hz, within an order of magnitude from analytic calculations based on GrAl microstructure. This amenable nonlinearity, combined with the relatively high quality factors in the 105 range, open new avenues for applications in quantum information processing and kinetic inductance detectors.
arxiv pdf