A. D. K. Finck

Quasiparticle tunneling as a probe of Josephson junction quality and capacitor material in superconducting qubits

  1. C. Kurter,
  2. C. E. Murray,
  3. R.T. Gordon,
  4. B. B. Wymore,
  5. M. Sandberg,
  6. R. M. Shelby,
  7. A. Eddins,
  8. V. P. Adiga,
  9. A. D. K. Finck,
  10. E. Rivera,
  11. A.A. Stabile,
  12. B. Trimm,
  13. B. Wacaser,
  14. K. Balakrishnan,
  15. A. Pyzyna,
  16. J. Sleight,
  17. M. Steffen,
  18. and K. Rodbell
Non-equilibrium quasiparticles are possible sources for decoherence in superconducting qubits because they can lead to energy decay or dephasing upon tunneling across Josephson junctions.
Here, we investigate the impact of the intrinsic properties of two-dimensional transmon qubits on quasiparticle tunneling (QPT) and discuss how we can use QPT to gain critical information about the Josephson junction quality and device performance. We find the tunneling rate of the non-equilibrium quasiparticles to be sensitive to the choice of the shunting capacitor material and their geometry in qubits. In some devices, we observe an anomalous temperature dependence of the QPT rate below 100 mK that deviates from a constant background associated with non-equilibrium quasiparticles. We speculate that high transmission sites within the Josephson junction’s tunnel barrier can lead to this behavior, which we can model by assuming that the defect sites have a smaller effective superconducting gap than the leads of the junction. Our results present a unique characterization tool for tunnel barrier quality in Josephson junctions and shed light on how quasiparticles can interact with various elements of the qubit circuit.
arxiv pdf

Suppressed crosstalk between two-junction superconducting qubits with mode-selective exchange coupling

  1. A. D. K. Finck,
  2. S. Carnevale,
  3. D. Klaus,
  4. C. Scerbo,
  5. J. Blair,
  6. T.G. McConkey,
  7. C. Kurter,
  8. A. Carniol,
  9. G. Keefe,
  10. M. Kumph,
  11. and O. E. Dial
Fixed-frequency qubits can suffer from always-on interactions that inhibit independent control. Here, we address this issue by experimentally demonstrating a superconducting architecture
using qubits that comprise of two capacitively-shunted Josephson junctions connected in series. Historically known as tunable coupling qubits (TCQs), such two-junction qubits support two modes with distinct frequencies and spatial symmetries. By selectively coupling only one type of mode and using the other as our computational basis, we greatly suppress crosstalk between the data modes while permitting all-microwave two-qubit gates.
arxiv pdf