L. Grünhaupt

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

Bi-stability in a Mesoscopic Josephson Junction Array Resonator

  1. P.R. Muppalla,
  2. O. Gargiulo,
  3. S.I. Mirzaei,
  4. B. Prasanna Venkatesh,
  5. M.L. Juan,
  6. L. Grünhaupt,
  7. I.M. Pop,
  8. and G. Kirchmair
We present an experimental investigation of the switching dynamics of a stochastic bistability in a 1000 Josephson junctions array resonator with a resonance frequency in the GHz range.
As the device is in the regime where the anharmonicity is on the order of the linewidth, the bistability appears for a drive strength of only a few photons. We measure the dynamics of the bistability by continuously observing the jumps between the two metastable states, which occur with a rate ranging from a few Hz down to a few mHz. The switching rate strongly depends on the drive strength, pump strength and the temperature, following Kramer’s law. The interplay between nonlinearity and coupling, in this little explored regime, could provide a new resource for nondemolition measurements, single photon switches or even elements for autonomous quantum error correction.
arxiv pdf